±0.10°C Accuracy, 16-Bit, Digital I2C
Temperature Sensor for VSM Applications
ADT7422

Data SheetFEATURES

GENERAL DESCRIPTION

Accuracy meets clinical thermometry specification of the
ASTM E1112 when soldered onto the final PCB±0.10°C from 25°C to 50°C at 3.0 V±0.25°C from −20°C to +105°C at 2.7 V to 3.3 V
Ultralow temperature drift: 0.0073°C
National Institute of Standards and Technology (NIST)
traceable or equivalent
Fast first temperature conversion at power-up of 6 ms
Simple implementation
No temperature calibration or correction required
No linearity correction required
Low power
140 μW typical at 3.0 V in 1 SPS mode
6 μW typical at 3.0 V in shutdown mode
Programmable interrupts
Critical overtemperature interrupt
Overtemperature and undertemperature interrupt
I2C-compatible interface
16-lead, 4 mm × 4 mm, RoHS compliant LFCSPThe ADT7422 is a high accuracy, digital I2C temperature sensor
designed to meet the clinical thermometry specification of the
ASTM E1112 standards when soldered onto the final printed
circuit board (PCB).
The ADT7422 contains an internal band gap reference, atemperature sensor, and a precision analog-to-digital converter(ADC). The ADT7422 provides a 16-bit temperature resultwith a resolution of 0.0078°C and an accuracy of up to ±0.10°C
across the temperature range of 25°C to 50°C without the needfor calibration after the PCB soldering process.
Operating at 3.0 V, the average supply current is typically 210 μA.
The ADT7422 has a shutdown mode that powers down thedevice and offers a shutdown current of typically 2.0 μA at 3.0 V.
The ADT7422 is rated for operation over the −40°C to +125°C
temperature range.
Pin A0 and Pin A1 are available for address selection and provide
four possible I2C addresses for the ADT7422. The CT pin is an
open-drain output that becomes active when the temperature
exceeds a programmable critical temperature limit. The INT pin isalso an open-drain output that becomes active when thetemperature exceeds a programmable limit. The INT pin andCT pin can operate in comparator and interrupt event modes.

APPLICATIONS
Vital signs monitoring (VSM)
Medical equipment
Resistance temperature detector (RTD) and thermistor
replacement
Food transportation and storage
Thermocouple cold junction compensation
Environmental monitoring and heating, ventilation, and air
conditioning (HVAC)
Laser diode temperature control

PRODUCT HIGHLIGHTS
1.
2.
3.
4.

No calibration or correction required by the user.
Low power consumption.
Long-term stability and reliability.
High accuracy for industrial, instrumentation, and medical
applications.

FUNCTIONAL BLOCK DIAGRAM

GND 11

INTERNAL
OSCILLATORINTERNAL
REFERENCETEMPERATURESENSOR

ADT7422
A0 3
A1 4

Σ-Δ
MODULATORFILTER
LOGIC

10

CT

9

INT

1

SCL

2

SDA

TCRIT

THIGH

TLOW

I2C INTERFACE

20961-001

VDD 12

Figure 1.

Rev. 0Document Feedback

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Tel: 781.329.4700©2020 Analog Devices, Inc. All rights reserved.

Technical Support

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ADT7422

Data SheetTABLE OF CONTENTS
Features .............................................................................................. 1

Temperature Value Registers .................................................... 12

Applications ....................................................................................... 1

Status Register ............................................................................. 13

General Description ......................................................................... 1

Configuration Register .............................................................. 13

Product Highlights ........................................................................... 1

THIGH Setpoint Registers ............................................................. 14

Functional Block Diagram .............................................................. 1

TLOW Setpoint Registers.............................................................. 14

Revision History ............................................................................... 2

TCRIT Setpoint Registers.............................................................. 14

Specifications..................................................................................... 3

THYST Setpoint Register............................................................... 152

I C Timing Specifications ............................................................ 4

ID Register................................................................................... 15

Absolute Maximum Ratings............................................................ 5

Serial Interface ................................................................................ 16

Thermal Resistance ...................................................................... 5

Serial Bus Address ...................................................................... 16

ESD Caution .................................................................................. 5

Writing Data ............................................................................... 17

Pin Configuration and Function Descriptions ............................. 6

Reading Data............................................................................... 18

Typical Performance Characteristics ............................................. 7

Reset ............................................................................................. 19

Theory of Operation ........................................................................ 9

General Call ................................................................................ 19

Circuit Information ...................................................................... 9

INT and CT Outputs...................................................................... 20

Converter Details.......................................................................... 9

Undertemperature and Overtemperature Detection ............ 20

Normal Mode ................................................................................ 9

Applications Information .............................................................. 22

One Shot Mode ............................................................................. 9

Thermal Response Time ........................................................... 22

1 SPS Mode .................................................................................. 10

Supply Decoupling ..................................................................... 22

Shutdown Mode.......................................................................... 10Powering from a Switching Regulator ..................................... 22

Fault Queue ................................................................................. 10

Temperature Measurement ....................................................... 22

Temperature Data Format ......................................................... 11

Quick Guide to Measuring Temperature ................................ 22

Temperature Conversion Formulas ......................................... 11

Outline Dimensions ....................................................................... 23

Registers ........................................................................................... 12

Ordering Guide .......................................................................... 23

Address Pointer Register ........................................................... 12

REVISION HISTORY
1/2020—Revision 0: Initial Version

Rev. 0 | Page 2 of 23

Data Sheet

ADT7422

SPECIFICATIONSTA = −40°C to +125°C, VDD = 2.7 V to 3.3 V, unless otherwise noted.
Table 1.
Parameter
TEMPERATURE SENSOR AND ADC
Accuracy1

SymbolMin

Typ

ADC Resolution

Temperature Resolution
13-Bit16-BitTemperature Conversion Time
Fast Temperature Conversion Time
1 SPS Mode Conversion Time
Temperature Hysteresis3
Repeatability
Drift4DC Power Supply Rejection Ratio(PSRR)DIGITAL OUTPUTS (CT, INT, SDA—
OPEN-DRAIN)High Output Leakage Current
Output Low Voltage
Output High Voltage
Output Capacitance
DIGITAL INPUTS (SCL, SDA, A0, A1)
Input Current
Input Low Voltage

Input High Voltage

IOH
VOL
VOH
COUT

Unit

Test Conditions/Comments±0.102
±0.25
±0.50
13

°C
°C
°C
Bits

16

Bits

TA = 25°C to 50°C, VDD = 3.0 V
TA = −20°C to +105°C, VDD = 2.7 V to 3.3 V
TA = −40°C to +125°C, VDD = 2.7 V to 3.3 V
Twos complement temperature value ofthe sign bit plus 12 ADC bits
Twos complement temperature value ofthe sign bit plus 15 ADC bit

0.06250.0078125
240

°C
°C
ms

6
60
±0.002±0.0150.0073
0.1

ms
ms
°C
°C
°C
°C/V

0.1

CT pin and INT pin pulled up to VDD
Low output leakage current (IOL) = 1 mA at
3.3 V

±1
0.3 ×
VDD
0.4

μA
V

Input voltage (VIN) = 0 V to VDD
SCL and SDA only

V
V
V
ns

A0 and A1 only
SCL and SDA only
A0 and A1 only
Input filtering suppresses noise spikes of<50 ns

2

10

pF

3.0
210
46
2.0
700
140
6

3.3
265

V
μA
μA
μA
μW
μW
μW

0.7 × VDD
2
50

2.7

μA
V

13-bit resolution (sign + 12 bits)
16-bit resolution (sign + 15 bits)
Continuous conversion and one-shot
conversion modes
First conversion on power-up only
Conversion time for 1 SPS mode
Temperature cycle = 25°C to 125°C to 25°C
TA = 25°C, average of 10 readings
500-hour stress test at 150°C
TA = 25°C

V
pF

2

VIL

VIH

5
0.4

0.7 × VDDSCL and SDA Glitch Rejection
Pin Capacitance
POWER REQUIREMENTS
Supply Voltage
Supply Current
1 SPS Current
Shutdown Current
Power Dissipation Normal Mode
Power Dissipation 1 SPSPower Dissipation Shutdown Mode

Max

1

15

VDD = 3.3 V while converting, I2C inactive
VDD = 3.3 V in 1 SPS mode, TA = 25°C
VDD = 3.3 V
VDD = 3.3 V, TA = 25°C
VDD = 3.0 V, TA = 25°C
VDD = 3.0 V, TA = 25°C

The accuracy specification includes repeatability.
These limits represent a 3-sigma distribution when devices are soldered to the PCB using a 16-point rolling average filter with a 300 ms sample period with the device
in continuous conversion mode.
3
The temperature hysteresis specification does not include repeatability.
4
Drift includes solder heat resistance and lifetime test performed as per JEDEC Standard JESD22-A108.
2

Rev. 0 | Page 3 of 23

ADT7422

Data Sheet

I2C TIMING SPECIFICATIONSTA = −40°C to +125°C, VDD = 2.7 V to 3.3 V, unless otherwise noted. All input signals are specified with rise time (tR) = fall time (tF) = 5 ns
(10% to 90% of VDD) and timed from a voltage level of 1.6 V.
Table 2.
Parameter
SERIAL INTERFACE

SymbolSCL Frequency
SCL High Pulse Width
SCL Low Pulse Width
SCL and SDA Rise TimeSCL and SDA Fall Time
Hold Time (Start Condition)
Setup Time (Start Condition)
Data Setup Time
Setup Time (Stop Condition)
Data Hold Time (Master)Bus Free Time (Between Stop and Start Condition)
Capacitive Load for Each Bus Line

Min

Typ

0
0.6
1.3

tHIGH
tLOW
tR
tF
tHD:STAtSU:STAtSU:DATtSU:STOtHD:DAT
tBUF
CB

Max

Unit

400

kHz
μs
μs
μs
μs
μs
μs
μs
μs
μs
μs
pF

0.3
0.3
0.6
0.6
0.02
0.6
0.03
1.3
400

Test Conditions/Comments
See Figure 2. Sample tested during
development to ensure compliance.

After this period, the first clock is generated.
Relevant for repeated start condition.

Timing Diagram
tLOW

tR

tF

tHD:STASCLtHD:DATtHIGH

tSU:DATtSU:STAtSU:STO
20961-002

tHD:STASDAtBUF

Figure 2. Serial Interface Timing Diagram

Rev. 0 | Page 4 of 23

Data Sheet

ADT7422

ABSOLUTE MAXIMUM RATINGSTA = 25°C, unless otherwise noted.

THERMAL RESISTANCE

Table 3.

Thermal performance is directly linked to PCB design andoperating environment. Close attention to PCB thermal design
is required. θJA and θJC are specified for a device soldered on a
JEDEC 4-layer test board for surface-mount packages with
16 thermal vias. The values listed in Table 4 are based on
simulated data.

Parameter
VDD to GND
SDA Voltage to GNDSCL Output Voltage to GND
A0 Input Voltage to GND
A1 Input Voltage to GND
CT and INT Output Voltage to GND
Operating Temperature Range
Storage Temperature Range
Maximum Junction Temperature
ESD
Human Body Model (HBM)
Field Induced Charge Device Model(FICDM)
Reflow Soldering (Pb-Free)
Peak Temperature
Time at Peak Temperature

Rating−0.3 V to +7 V
−0.3 V to VDD + 0.3 V−0.3 V to VDD + 0.3 V−0.3 V to VDD + 0.3 V−0.3 V to VDD + 0.3 V−0.3 V to VDD + 0.3 V−40°C to +125°C−65°C to +150°C
150°C

Table 4. Thermal Resistance
Package Type
CP-16-17

ESD CAUTION
2 kV
1 kV
JEDEC J-STD-020
260°C
10 sec to 40 sec

Stresses at or above those listed under Absolute Maximum
Ratings may cause permanent damage to the product. This is a
stress rating only; functional operation of the product at theseor any other conditions above those indicated in the operational
section of this specification is not implied. Operation beyond
the maximum operating conditions for extended periods may
affect product reliability.

Rev. 0 | Page 5 of 23

θJA
37

θJC
33

Unit
°C/W

ADT7422

Data Sheet

13 NIC

14 NIC

15 NIC

16 NICPIN CONFIGURATION AND FUNCTION DESCRIPTIONS

SCL 1

A0 3

12 VDD

ADT7422
TOP VIEW(Not to Scale)

10 CT
INT

NIC 8

NIC 7

NIC 6

9
NIC 5

A1 4

11 GND

NOTES
1. NIC = NOT INTERNALLY CONNECTED. THE NIC PINS ARE NOT BONDED TO THE DIE INTERNALLY.
2. EXPOSED PAD. TO ENSURE CORRECT OPERATION, EITHER LEAVE THE EXPOSED PAD
FLOATING OR CONNECT THE EXPOSED PAD TO GROUND. SOLDER THE EXPOSED PAD
TO A PAD ON THE PCB TO CONFER MECHANICAL STRENGTH TO THE PACKAGE.

20961-003

SDA 2

Figure 3. Pin Configuration

Table 5. Pin Function Descriptions
Pin No.
1

Mnemonic
SCL

2

SDA

3
4
5 to 8, 13 to 16
9

A0
A1
NIC
INT

10

CT

11
12

GND
VDD
EPAD

Description
I2C Serial Clock Input, Open-Drain Configuration. The serial clock is used to clock in and clock out data to
and from any register of the ADT7422. A pull-up resistor of typically 10 kΩ is required.
I2C Serial Data Input/Output, Open-Drain Configuration. Serial data to and from the device is provided on
this pin. A pull-up resistor of typically 10 kΩ is required.
I2C Serial Bus Address Selection Pin, Logic Input. Connect this pin to GND or VDD to set an I2C address.
I2C Serial Bus Address Selection Pin, Logic Input. Connect this pin to GND or VDD to set an I2C address.
Not Internally Connected. The NIC pins are not bonded to the die internally.
Overtemperature and Undertemperature Indicator, Logic Output, Open-Drain Configuration. Power-up
default setting is an active low comparator interrupt. A pull-up resistor of typically 10 kΩ is required.
Critical Overtemperature Indicator, Logic Output, Open-Drain Configuration. Power-up default polarity is
active low. A pull-up resistor of typically 10 kΩ is required.
Analog and Digital Ground.
Positive Supply Voltage (2.7 V to 3.3 V). The supply can be decoupled with a 0.1 μF ceramic capacitor to ground.
Exposed Pad. To ensure correct operation, either leave the exposed pad floating or connect the exposed
pad to ground. Solder the exposed pad to a pad on the PCB to confer mechanical strength to the package.

Rev. 0 | Page 6 of 23

Data Sheet

ADT7422

TYPICAL PERFORMANCE CHARACTERISTICS
0.035

0.25
0.20

0.030
STANDARD DEVIATION (°C)

0.10
0.05
0
–0.05
–0.10
–0.15

0.025
0.020
0.015
0.010
0.005

–0.20

35

36

37

38

39

40

41

0

20961-004

–0.25
42

TEMPERATURE (°C)

Figure 4. VSM Temperature Range of the EVAL-ADT7422MBZ Post Soldering
to JEDEC J-STD-020, VDD = 3 V

35

36

37

38

39

40

41

20961-107

SENSOR ERROR (°C)

0.15

42

TEMPERATURE (°C)

Figure 7. Standard Deviation of the EVAL-ADT7422MBZ Post Soldering to
JEDEC J-STD-020, VDD = 3 V

0.25

50

0.20
0.15

NUMBER OF HITS

SENSOR ERROR (°C)

40
0.10
0.05
0
–0.05

30

20

–0.10
–0.15

10

25

30

35
40
TEMPERATURE (°C)

45

0
–0.09

20961-005

–0.25
50

Figure 5. Narrow Temperature Range of the EVAL-ADT7422MBZ Post
Soldering to JEDEC J-STD-020, VDD = 3 V

–0.06

–0.03

0

0.03

0.06

0.09

SENSOR ERROR (°C)

20961-108–0.20

Figure 8. Histogram Distribution of Factory Calibration Error at 38°C for
170 Devices, VDD = 3 V
0.09

0.25
0.20

0.06

0.10

SENSOR ERROR (°C)

SENSOR ERROR (°C)

0.15

0.05
0
–0.05
–0.10
–0.15

0.03

0

–0.03

–0.06

–10

0

10

20

30

40

50

TEMPERATURE (°C)

60

70

80

Figure 6. Wide Temperature Range of the EVAL-ADT7422MBZ Post Soldering
to JEDEC J-STD-020, VDD = 3 V

Rev. 0 | Page 7 of 23

–0.09
0

30

60

90
120
DEVICE NUMBER

150

180

Figure 9. Factory Calibration Error at 38°C for 170 Devices, VDD = 3 V

20961-109

–0.25
–20

20961-006–0.20

Data Sheet

30

300

25

250

20

200

IDD (µA)

15

10

150

100

5

50

3.3V
3.0V
2.7V
–50

0
50
100
TEMPERATURE (°C)

150

1SPS

200

20961-007

0–100

Figure 10. Shutdown Operating Supply Current (IDD) vs. Temperature for
Various Voltages

140
125°C
120
105°C
100
85°C
80
IT TAKES LESS THAN
2 SECONDS TO REACH 63.2%
OF TEMPERATURE SPAN

60
40
20
0
0

5

10

15

20

25

TIME (s)20961-008

TEMPERATURE (°C)

CONTINUOUS
CONVERSION

Figure 11. Thermal Response Time for Various Temperatures

Rev. 0 | Page 8 of 23

0
–100

–50

0

50

100

TEMPERATURE (°C)

Figure 12. IDD vs. Temperature at 3 V

150

200

20961-009

IDD (µA)

ADT7422

Data Sheet

ADT7422

THEORY OF OPERATIONCIRCUIT INFORMATIONNORMAL MODE
2

The ADT7422 is a high accuracy, digital I C temperature sensor
that uses a 16-bit ADC to monitor and digitize the temperature
to 0.0078°C of resolution. The ADC resolution, by default, is set
to 13 bits (0.0625°C). An internal temperature sensor generates
a voltage proportional to absolute temperature, which is compared
to an internal voltage reference and input into a precision digitalmodulator (see Figure 13).
The internal temperature sensor has high accuracy and linearity
over the entire rated temperature range without needing correction
or calibration by the user.
The sensor output is digitized by a Σ-Δ modulator, also known as
the charge balance type ADC. This type of converter utilizes
time domain oversampling and a high accuracy comparator todeliver 16 bits of resolution in a compact circuit.

CONVERTER DETAILSThe Σ-Δ modulator consists of an input sampler, a summing
network, an integrator, a comparator, and a 1-bit digital-to-analog
converter (DAC). This architecture creates a negative feedback
loop and minimizes the integrator output by changing the duty
cycle of the comparator output in response to input voltagechanges. The comparator samples the output of the integrator at ahigher rate than the input sampling frequency. This oversamplingspreads the quantization noise over a wider band than that of
the input signal, which improves overall noise performance andincreases accuracy.
Σ-Δ MODULATORINTEGRATORCOMPARATORVOLTAGEREFERENCE
AND V PTAT1

At power-up, the first conversion is a fast conversion andtypically takes 6 ms. If the temperature exceeds 147°C, the CT pin
asserts low. If the temperature exceeds 64°C, the INT pin asserts
low. Fast conversion temperature accuracy is typically within ±5°C.
The conversion clock for the device is generated internally.
No external clock is required except when reading from andwriting to the serial port.
The measured temperature value is compared with a criticaltemperature limit (stored in the 16-bit TCRIT setpoint read/write
register), a high temperature limit (stored in the 16-bit THIGH
setpoint read/write register), and a low temperature limit(stored in the 16-bit TLOW setpoint read/write register). If themeasured value exceeds these limits, the INT pin is activated. If themeasured value exceeds the TCRIT limit, the CT pin is activated. The
INT pin and CT pin are programmable for both polarity via theconfiguration register (Register Address 0x03) and interrupt mode
via the configuration register (Register Address 0x03).

ONE SHOT MODE
To enable one shot mode, set Bit 6 to 0 and Bit 5 to 1 in theconfiguration register (Register Address 0x03). When this modeis enabled, the ADT7422 immediately completes a conversion
and then goes into shutdown mode.

1-BIT
DAC

DIGITAL
LOW-PASSFILTER

13-BIT/
16-BIT

TEMPERATUREVALUEREGISTER

1V
PTAT IS A VOLTAGE PROPORTIONAL TO ABSOLUTE TEMPERATURE.

20961-010

1-BIT
CLOCK
GENERATOR

In normal mode (default power-up mode) the ADT7422 runs anautomatic conversion sequence. During this automatic conversion
sequence, a conversion typically takes 240 ms to complete. The
ADT7422 continuously converts during the sequence and as soon
as one temperature conversion is complete, another temperature
conversion begins. Each temperature conversion result is stored
in the 16-bit temperature value register, which consists of the
8-bit temperature value most significant byte register and the
8-bit temperature value least significant byte register (see Table 7),
and is available through the I2C interface. In continuous
conversion mode, the read operation provides the most recent
converted result.

Figure 13. Σ-Δ Modulator

The ADT7422 can operate in four operating modes: normal, one
shot, 1 SPS, and shutdown.

Wait for a minimum of 240 ms after writing to the operation mode
bits before reading back the temperature from the temperature
value at Register Address 0x00 and Register Address 0x01, asshown in Table 7. This time ensures that the ADT7422 has time
to power up and complete a conversion.
To obtain an updated temperature conversion, reset Bit 6 to 0 and
Bit 5 to 1 in the configuration register (Register Address 0x03).
One shot mode is useful when a circuit design priority is to
reduce power consumption.

Rev. 0 | Page 9 of 23

ADT7422

Data Sheet

CT and INT Operation in One Shot Mode
See Figure 14 for more information on one shot mode CT pin
operation for TCRIT overtemperature events when one of thelimits is exceeded. Note that in interrupt mode, a read from any
register resets the INT pin and CT pin.
In comparator mode, if the temperature drops below THIGH − THYST
or goes above TLOW + THYST, a write to the operation mode bits
(Register Address 0x03, Bits[6:5]) resets the INT pin.
In comparator mode, if the temperature drops below TCRIT − THYST,a write to the operation mode bits (Register Address 0x03,
Bits[6:5]) resets the CT pin (see Figure 14).
When using one shot mode, ensure that the appropriate refresh
rate is used for the given application.

1 SPS MODE
In 1 SPS mode, the device performs one measurement per second.
A conversion typically takes 60 ms and the device remains in theidle state for the remaining 940 ms period. To enable 1 SPS mode,
write 1 to Bit 6 and 0 to Bit 5 of the configuration register(Register Address 0x03).

SHUTDOWN MODE

conversions are initiated until the ADT7422 is taken out of
shutdown mode. To take the ADT7422 out of shutdown mode,
write 0 to Bit 6 and Bit 5 in the configuration register (Register
Address 0x03). The ADT7422 typically takes 1 ms (with a 0.1 μF
decoupling capacitor) to exit shutdown mode. The conversion
result from the last conversion prior to shutdown can still beread from the ADT7422 when the device is in shutdown mode.
When the device is taken out of shutdown mode, the internal
clock starts and a conversion is initiated.

FAULT QUEUE
Bit 0 and Bit 1 of the configuration register (Register Address 0x03)
are used to set up a fault queue. The queue can facilitate up to four
fault events to prevent false tripping of the INT pin and CT pin
when the ADT7422 is used in a noisy temperature environment.
The number of faults set in the queue must occur consecutively
to set the INT and CT outputs. For example, if the number offaults set in the queue is four, four consecutive temperature
conversions must occur with each result exceeding a temperature
limit in any of the limit registers before the INT pin and CT pin
are activated. If two consecutive temperature conversions exceed atemperature limit and the third conversion does not, the fault
count is reset back to zero.

To place the ADT7422 in shutdown mode, write 1 to Bit 6 andBit 5 of the configuration register (Register Address 0x03), in
which case the entire IC is shut down and no further
TEMPERATURE
149°C
148°C
TCRIT

147°C
146°C
145°C
144°C
143°C

TCRIT – THYST

142°C
141°C
140°C

CT PIN
POLARITY = ACTIVE LOWCT PIN
POLARITY = ACTIVE HIGH
TIME
WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATIONREGISTER.*WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATIONREGISTER.**THERE IS A 240ms DELAY BETWEEN WRITING TO THE CONFIGURATION REGISTER TO STARTA STANDARD ONE SHOT CONVERSION AND TO ACTIVATE THE CT PIN DUE TO THE DELAY IS
60ms IN THE CASE OF A ONE SHOT CONVERSION.

Figure 14. One Shot CT Pin

Rev. 0 | Page 10 of 23

20961-011

WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATIONREGISTER.*

Data Sheet

ADT7422

TEMPERATURE DATA FORMATTEMPERATURE CONVERSION FORMULAS

One LSB of the ADC corresponds to 0.0625°C in 13-bit mode
or 0.0078°C in 16-bit mode. The ADT7422 can measure atemperature range of 255°C, and is guaranteed to measure a low
value temperature limit of −40°C to a high value temperature
limit of +125°C. The temperature measurement result is stored
in the 16-bit temperature value register and is compared withthe high temperature limits stored in the 16-bit TCRIT setpoint
register (consisting of the 8-bit TCRIT setpoint most significant
byte register and the 8-bit TCRIT setpoint least significant byte
register) and the 16-bit THIGH setpoint register (consisting of the
8-bit THIGH setpoint most significant byte register and the 8-bit
THIGH setpoint least significant byte register). The temperature
value is also compared to the low temperature limit stored in the
TLOW setpoint register, which consists of the 8-bit TLOW setpoint
most significant byte register and the 8-bit TLOW setpoint leastsignificant byte register.

16-Bit Temperature Data Format

Temperature data in the temperature value register, the TCRIT
setpoint register, the THIGH setpoint register, and the TLOW setpoint
register are represented by a 13-bit twos complement word.
The MSB is the temperature sign bit. The three LSBs, Bits[2:0], at
power-up, are not part of the temperature conversion result andare flag bits for TCRIT, THIGH, and TLOW. Table 6 shows the 13-bit
temperature data format without Bits[2:0].
To extend the number of bits in the temperature data-word to
16 bits (twos complement), set Bits[7:1] in the configuration
register (Register Address 0x03). When using a 16-bit temperature
data value, Bits[2:0] are not used as flag bits and are the LSB bitsof the temperature value instead. The power-on default setting
has a 13-bit temperature data value.
A 2-byte read is required to read back the temperature from thetemperature value register. The ADT7422 can still be used with a
9-bit temperature data format if the last four LSBs of the 13-bit
temperature value are ignored. These four LSBs are Bits[6:3] inTable 6.
Table 6. 13-Bit Temperature Data Format
Temperature
−40°C
−25°C
−0.0625°C
0°C+0.0625°C+25°C+105°C+125°C+150°C

Digital Output (Binary)
Bits[15:3]
1 1101 1000 0000
1 1110 0111 0000
1 1111 1111 1111
0 0000 0000 0000
0 0000 0000 0001
0 0001 1001 0000
0 0110 1001 0000
0 0111 1101 0000
0 1001 0110 0000

Digital Output(Hexadecimal)
0x1D800x1E700x1FFF
0x000
0x001
0x190
0x690
0x7D0
0x960

Use the following formulas to calculate the measured
temperatures in °C from the ADT7422 output codes in 16-bit
format:Positive Temperature = ADC Code (Decimal)/128
Negative Temperature = (ADC Code (Decimal) −65,536)/128
where ADC Code uses all 16 bits of the data byte, including thesign bit.
Negative Temperature = (ADC Code (Decimal) −32,768)/128
where Bit 15 (sign bit) is removed from the ADC code.

13-Bit Temperature Data Format
Use the following formulas to calculate the measured
temperatures in °C from the ADT7422 output codes in 13-bit
format:Positive Temperature = ADC Code (Decimal)/16
Negative Temperature = (ADC Code (Decimal) − 8192)/16
where ADC Code uses the first 13 MSBs of the data byte,
including the sign bit.
Negative Temperature = (ADC Code (Decimal) − 4096)/16
where Bit 15 (sign bit) is removed from the ADC code.

10-Bit Temperature Data Format
Use the following formulas to calculate the measured
temperatures in °C from the ADT7422 output codes in 10-bit
format:Positive Temperature = ADC Code (Decimal)/2
Negative Temperature = (ADC Code (Decimal) − 1024)/2
where ADC Code uses all 10 bits of the data byte, including thesign bit.
Negative Temperature = (ADC Code (Decimal) − 512)/2
where Bit 9 (sign bit) is removed from the ADC code.

9-Bit Temperature Data Format
Use the following formulas to calculate the measured
temperatures in °C from the ADT7422 output codes in 9-bit
format:Positive Temperature = ADC Code (Decimal)
Negative Temperature = ADC Code (Decimal) − 512
where ADC Code uses all nine bits of the data byte, including
the sign bit.
Negative Temperature = ADC Code (Decimal) − 256
where Bit 8 (sign bit) is removed from the ADC code.

Rev. 0 | Page 11 of 23

ADT7422

Data SheetREGISTERSThe ADT7422 contains 13 registers, as shown in Table 7, andthe address pointer register. The registers include the following: Nine temperature registers
 One status register One ID register One configuration register One address pointer register One software reset
All registers are 8 bits wide. The temperature value registers, thestatus register, and the ID register are read only. The software reset
register is a write only register. At power-up, the address pointerregister is loaded with 0x00 and points to the temperature value
most significant byte register (Register Address 0x00) (see Table 7).
Table 7. Registers
Register
Address
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
0x0C
0x0D
0x2E
0x2F

Power-On
Default
0x00
0x00
0x00
0x00
0x20 (64°C)
0x00 (64°C)
0x05 (10°C)
0x00 (10°C)
0x49 (147°C)
0x80 (147°C)
0x05 (5°C)
0xCB
0xXX
0xXX
0xXX
0xXX

Description
Temperature value most significant byte
Temperature value least significant byte
StatusConfiguration
THIGH setpoint most significant byte
THIGH setpoint least significant byte
TLOW setpoint most significant byte
TLOW setpoint least significant byte
TCRIT setpoint most significant byte
TCRIT setpoint least significant byte
THYST setpoint
ID
Reserved
Reserved
Reserved
Software reset

ADDRESS POINTER REGISTER
The address pointer register is always the first register written toduring a write to the ADT7422. Set the address point register tothe address of the register to which the write or read transaction
is intended. Table 7 shows the register address of each registeron the ADT7422. The default value of the address pointerregister is 0x00.
Table 8. Address Pointer Register
P7
ADD7

P6
ADD6

P5
ADD5

P4
ADD4

P3
ADD3

P2
ADD2

P1
ADD1

P0
ADD0

TEMPERATURE VALUE REGISTERS
The temperature value consists of two bytes, one most significant
byte and one least significant byte. These values can be read intwo separate 1-byte reads or in a single 2-byte read. Only theaddress of the most significant byte must be loaded into the address
pointer register for a 2-byte read. After the most significant byte isread, the address pointer is auto-incremented so that the leastsignificant byte can be read within the same transaction.
Bit 0 to Bit 2 are event alarm flags for the TLOW, THIGH, and TCRIT
setpoint most significant byte registers and least significant byte
registers. When the ADC is configured to convert the temperature
to a 16-bit digital value, Bit 0 to Bit 2 are no longer used as flag
bits and are used as the LSBs for the extended digital value instead.

Table 9. Temperature Value Most Significant Byte Register (Register Address 0x00)
Bit[14:8]
15

Default Value
0000000
0

Type
R
R

Name
Temp
Sign

Description
Temperature value in twos complement format
Sign bit, indicates if the temperature value is negative or positive

Table 10. Temperature Value Least Significant Byte Register (Register Address 0x01)
Bit
0Default
Value
0

Type
R

Name
TLOW flag/LSB0

1

0

R

THIGH flag/LSB1

2

0

R

TCRIT flag/LSB2

[7:3]

00000

R

Temp

Description
Flags a TLOW event if the configuration register, Register Address 0x03, Bit 7 = 0 (13-bit resolution).
When the temperature value is below TLOW, this bit is set to 1.
Contains the least significant bit, Bit 0, of the 15-bit temperature value if the configuration register,
Register Address 0x03, Bit 7 = 1 (16-bit resolution).
Flags a THIGH event if the configuration register, Register Address 0x03, Bit 7 = 0 (13-bit resolution).
When the temperature value is above THIGH, this bit is set to 1.
Contains the least significant bit, Bit 1, of the 15-bit temperature value if the configuration register,
Register Address 0x03, Bit 7 = 1 (16-bit resolution).
Flags a TCRIT event if the configuration register, Register Address 0x03, Bit 7 = 0 (13-bit resolution).
When the temperature value exceeds TCRIT, this bit is set to 1.
Contains the least significant bit, Bit 2, of the 15-bit temperature value if the configuration register,
Register Address 0x03, Bit 7 = 1 (16-bit resolution).
Temperature value in twos complement format.

Rev. 0 | Page 12 of 23

Data Sheet

ADT7422STATUS REGISTERCONFIGURATION REGISTER

This 8-bit read only register reflects the status of theovertemperature and undertemperature interrupts that cancause the CT pin and INT pin to go active. The status register
also reflects the status of a temperature conversion operation.
The interrupt flags in this register are reset by a read operation
to the status register and/or when the temperature value returns
within the temperature limits, including hysteresis. The RDY bit isreset after a read from the temperature value registers. In one
shot mode and 1 SPS mode, the RDY bit is reset after a write tothe operation mode bits in the configuration register.

This 8-bit read/write register stores various configuration modes
for the ADT7422, including shutdown mode, overtemperatureand undertemperature interrupts, one shot mode, continuous
conversion mode, interrupt pins polarity, and overtemperaturefault queues.

Table 11. Status Register (Register Address 0x02)
Bit
[3:0]
4

Default
Value
0000
0

Type
R
R

Name
Unused
TLOW

5

0

R

THIGH

6

0

R

TCRIT

7

1

R

RDY

Description
Reads back 0.
This bit is set to 1 when the temperature goes below the TLOW temperature limit. The bit clears to 0 when
the status register is read and/or when the temperature measured goes back above the limit set in the
setpoint TLOW + THYST registers.
This bit is set to 1 when the temperature goes above the THIGH temperature limit. The bit clears to 0 when
the status register is read and/or when the temperature measured goes back below the limit set in the
setpoint THIGH − THYST registers.
This bit is set to 1 when the temperature goes above the TCRIT temperature limit. This bit clears to 0 when
the status register is read and/or when the temperature measured goes back below the limit set in the
setpoint TCRIT − THYST registers.
This bit goes low when the temperature conversion result is written into the temperature value register. It
is reset to 1 when the temperature value register is read. In one shot and 1 SPS modes, this bit is reset after
a write to the operation mode bits in the configuration register.

Table 12. Configuration Register (Register Address 0x03)
Bit
[1:0]

Default
Value
00

Type
R/W

Name
Fault queue

2

0

R/W

CT pin polarity

3

0

R/W

INT pin polarity

4

0

R/W

INT/CT mode

[6:5]

00

R/W

Operation mode

7

0

R/W

Resolution

Description
These two bits set the number of undertemperature/overtemperature faults that can occur before
setting the INT pin and CT pin. This helps to avoid false triggering due to temperature noise.
00 = 1 fault (default).
01 = 2 faults.
10 = 3 faults.
11 = 4 faults.
This bit selects the output polarity of the CT pin.
0 = active low.
1 = active high.
This bit selects the output polarity of the INT pin.
0 = active low.
1 = active high.
This bit selects between comparator mode and interrupt mode.
0 = interrupt mode.
1 = comparator mode.
These two bits set the operational mode for the ADT7422.
00 = continuous conversion (default). When one conversion is finished, the ADT7422 starts another.
01 = one shot. Conversion time is typically 240 ms.
10 = 1 SPS mode. Conversion time is typically 60 ms. This operational mode reduces the average
current consumption.
11 = shutdown. All circuitry except interface circuitry is powered down.
This bit sets up the resolution of the ADC when converting.
0 = 13-bit resolution. Sign bit + 12 bits gives a temperature resolution of 0.0625°C.
1 = 16-bit resolution. Sign bit + 15 bits gives a temperature resolution of 0.0078°C.

Rev. 0 | Page 13 of 23

ADT7422

Data Sheet
When reading from this register, the 8 MSBs (Bit 15 to Bit 8) areread first from Register Address 0x06 and then the 8 LSBs (Bit 7
to Bit 0) are read from Register Address 0x07. Only Register
Address 0x06 (TLOW setpoint most significant byte register)
must be loaded into the address pointer register because theaddress pointer auto-increments to Register Address 0x07 (TLOW
setpoint least significant byte register).

THIGH SETPOINT REGISTERS
The THIGH setpoint most significant byte register and the THIGH
setpoint least significant byte register store the overtemperature
limit value. An overtemperature event occurs when thetemperature value stored in the temperature value register
exceeds the value stored in this register. The INT pin is activated if
an overtemperature event occurs. The temperature is stored in
twos complement format with the most significant byte being
the temperature sign bit.

The default setting for the TLOW setpoint register is 10°C.

TCRIT SETPOINT REGISTERS

When reading from this register, the 8 MSBs (Bit 15 to Bit 8) areread first from Register Address 0x04, and then the 8 LSBs (Bit 7
to Bit 0) are read from Register Address 0x05 (THIGH setpoint
least significant byte register). Only Register Address 0x04
(THIGH setpoint most significant byte register) must be loaded
into the address pointer register because the address pointerauto-increments to Register Address 0x05 (THIGH setpoint leastsignificant byte register).

The TCRIT setpoint most significant byte register and the TCRIT
setpoint least significant byte register store the critical
overtemperature limit value. A critical overtemperature event
occurs when the temperature value stored in the temperature
value register exceeds the value stored in this register. The CT pin is
activated if a critical overtemperature event occurs. The
temperature is stored in twos complement format with the MSB
being the temperature sign bit.

The default setting for the THIGH setpoint register is 64°C.

When reading from this register, the 8 MSBs (Bit 15 to Bit 8) areread first from Register Address 0x08 (TCRIT setpoint mostsignificant byte register), and then the 8 LSBs (Bit 7 to Bit 0) areread from Register Address 0x09 (TCRIT setpoint least significant
byte register). Only Register Address 0x08 (TCRIT setpoint mostsignificant byte register) must be loaded into the address pointerregister because the address pointer auto-increments to Register
Address 0x09 (TCRIT setpoint least significant byte register).

TLOW SETPOINT REGISTERS
The TLOW setpoint most significant byte register and the TLOW
setpoint least significant byte register store the undertemperature
limit value. An undertemperature event occurs when thetemperature value stored in the temperature value register is lessthan the value stored in this register. The INT pin is activated if
an undertemperature event occurs. The temperature is stored in
twos complement format with the MSB being the temperature
sign bit.

The default setting for the TCRIT setpoint register is 147°C.

Table 13. THIGH Setpoint Most Significant Byte Register (Register Address 0x04)
Bit

Default Value

Type

Name

Description[15:8]

0x20

R/W

THIGH most significant byte

MSBs of the overtemperature limit, stored in twos complement format.

Table 14. THIGH Setpoint Least Significant Byte Register (Register Address 0x05)
Bit

Default Value

Type

Name

Description

[7:0]

0x00

R/W

THIGH least significant byte

LSBs of the overtemperature limit, stored in twos complement format.

Table 15. TLOW Setpoint Most Significant Byte Register (Register Address 0x06)
Bit

Default Value

Type

Name

Description[15:8]0x05

R/W

TLOW most significant byte

MSBs of the undertemperature limit, stored in twos complement format.

Table 16. TLOW Setpoint Least Significant Byte Register (Register Address 0x07)
Bit

Default Value

Type

Name

Description

[7:0]

0x00

R/W

TLOW least significant byte

LSBs of the undertemperature limit, stored in twos complement format.

Table 17. TCRIT Setpoint Most Significant Byte Register (Register Address 0x08)
Bit

Default Value

Type

Name

Description[15:8]

0x49

R/W

TCRIT most significant byte

MSBs of the critical overtemperature limit, stored in twos complement format.

Table 18. TCRIT Setpoint Least Significant Byte Register (Register Address 0x09)
Bit

Default Value

Type

Name

Description

[7:0]

0x80

R/W

TCRIT least significant byte

LSBs of the critical overtemperature limit, stored in twos complement format.

Rev. 0 | Page 14 of 23

Data Sheet

ADT7422

THYST SETPOINT REGISTERID REGISTER

This 8-bit read/write register stores the temperature hysteresis
value for the THIGH, TLOW, and TCRIT temperature limits. The
temperature hysteresis value is stored in straight binary format
using the four LSBs. Increments are possible in steps of 1°C
from 0°C to 15°C. The value in this register is subtracted fromthe THIGH and TCRIT values and added to the TLOW value to
implement hysteresis.

This 8-bit read only register stores the manufacture ID in Bit 3
to Bit 7 and the silicon revision in Bit 0 to Bit 2. The default
setting for the ID register is 0xCB.

Table 19. THYST Setpoint Register (Register Address 0x0A)
Bit

Default Value

Type

Name

Description

[3:0]

0101

R/W

THYST

Hysteresis value, from 0°C to 15°C. Stored in straight binary format. The default setting is 5°C.

[7:4]

0000

R/W

Not applicableNot used.

Table 20. ID Register (Register Address 0x0B)
Bit
[2:0]
[7:3]

Default Value
011
11001

Type
R
R

Name
Revision ID
Manufacture ID

Description
Contains the silicon revision identification number.
Contains the manufacture identification number.

Rev. 0 | Page 15 of 23

ADT7422

Data SheetSERIAL INTERFACE
Control of the ADT7422 is carried out via the I2C-compatible
serial interface. The ADT7422 is connected to this bus as a slave
and is under the control of a master device.

2.

Figure 15 shows a typical I2C interface connection.

SERIAL BUS ADDRESS
Like most I2C-compatible devices, the ADT7422 has a 7-bit
serial address. The five MSBs of this address for the ADT7422
are hardwired internally to 10010. Pin A1 and Pin A0 set the
two LSBs. These pins can be configured two ways, low and high,to give four different address options. Table 21 shows thedifferent bus address options available. The recommended
pull-up resistor value on the SDA and SCL lines is 10 kΩ.

3.

Table 21. I2C Bus Address Options
A5
0
0
0
0

A4
0
0
0
0

4.

A1
0
0
1
1

A0
0
1
0
1

Hexadecimal
0x48
0x49
0x4A
0x4B

The serial bus protocol operates as follows:1.

The master establishes a start condition to initiate datatransfer, defined as a high to low transition on the serial
data line (SDA) while the serial clock line (SCL) remains
high. The start condition indicates that an address and data
stream follow. All slave peripherals connected to the serial
bus respond to the start condition and shift in the next 8
bits consisting of a 7-bit address (MSB first) plus aread/write (R/W) bit. The R/W bit determines whether
data is written to or read from the slave device.
PULL-UP
VDD

It is not possible to mix reads and writes in one operation
because the type of operation is determined at the beginning of
the process and cannot subsequently be changed without
starting a new operation.

PULL-UP
VDD

10kΩ

10kΩ

VDD
VDD

10kΩ

10kΩ

ADT7422CT

TO INTERRUPT PIN
ON MICROCONTROLLER

PULL-UP
VDD

INT
A0
A1

SCL
SDA
GND

Figure 15. Typical I2C Interface Connection

Rev. 0 | Page 16 of 23

20961-012

A6
1
1
1
1

Binary
A3
A2
1
0
1
0
1
0
1
0

The peripheral with the address corresponding to thetransmitted address responds by pulling the data line low
during the low period before the ninth clock pulse known
as the acknowledge bit. All other devices on the bus thenremain idle while the selected device waits for data to beread from or written to it. If the R/W bit is set to 0, themaster writes to the slave device. If the R/W bit is set to 1,
the master reads from the slave device.
Data is sent over the serial bus in sequences of nine clock
pulses 8 bits of data followed by an acknowledge bit fromthe receiver of data. Transitions on the data line must occur
during the low period of the clock signal and remain stable
during the high period as a low to high transition when theclock is high, which can be interpreted as a stop signal.
When all data bytes have been read or written, stop
conditions are established. In write mode, the master pulls
the data line high during the 10th clock pulse to assert astop condition. In read mode, the master device pulls thedata line high during the low period before the ninth clock
pulse. This is known as a no acknowledge. The master firsttakes the data line low during the low period before the 10thclock pulse, then high during the 10th clock pulse to assert
a stop condition.

Data Sheet

ADT7422and the least significant byte registers in the same write
transaction. Writing two bytes of data to these registers requires
the serial bus address (the data register address of the mostsignificant byte register that is written to the address pointerregister) followed by the two data bytes written to the selected
data register. This sequence is shown in Figure 17.

WRITING DATA
It is possible to write either a single byte of data or two bytes of data
to the ADT7422, depending on which registers are to be written.
Writing a single byte of data requires the serial bus address (thedata register address that is written to the address pointerregister) followed by the data byte written to the selected dataregister. This sequence is shown in Figure 16.

If more than the required number of data bytes is written to aregister, the register ignores these extra data bytes. A start orrepeated start is required to write to a different register.

For the THIGH setpoint, TLOW setpoint, and TCRIT setpoint
registers, it is possible to write to both the most significant byte
1

9

1

9

SCL

1

SDA

0

0

1

0

A1

A0

P7

R/W

START BY
MASTER

P6

P5

P4

P3

P2

P1

P0

ACK. BY
ADT7422

ACK. BY
ADT7422

FRAME 1SERIAL BUS ADDRESS BYTE

FRAME 2ADDRESS POINTER REGISTER BYTE
19SCL (CONTINUED)

D6

D5

D4

D3

D2

D1

D0
ACK. BY
ADT7422

STOP BY
MASTERFRAME 3DATA BYTE

20961-013

D7

SDA (CONTINUED)

Figure 16. Writing to a Register Followed by a Single Byte of Data

1

9

1

9

SCL

SDA

1

0

0

1

0

A1

A0

P7

R/W

START BY
MASTER

P6

P5

P4

P3

P2

P1

P0

ACK. BY
ADT7422

ACK. BY
ADT7422

FRAME 1SERIAL BUS ADDRESS BYTE

FRAME 2ADDRESS POINTER REGISTER BYTE

1

9

1

9

SCL (CONTINUED)

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

FRAME 4DATA BYTE

FRAME 3DATA BYTE

Figure 17. Writing to a Register Followed by Two Bytes of Data

Rev. 0 | Page 17 of 23

D1

D0
ACK. BY
ADT7422

ACK. BY
ADT7422

STOP BY
MASTER

20961-014

SDA (CONTINUED)

ADT7422

Data Sheetcase of reading back from the 2-byte registers, the address pointerautomatically increments from the most significant byte register
address to the least significant byte register address.

READING DATA
Reading data from the ADT7422 is done in a single-byte data
operation for the configuration register, the status register, the
THYST setpoint register, and the ID register. A two-byte data read
operation is needed for the temperature value register, THIGH
setpoint register, TLOW setpoint register, and the TCRIT setpoint
register. Reading back the contents of the 8-bit configuration
register is shown in Figure 18. Reading back the contents of thetemperature value register is shown in Figure 19.

To read from another register, execute another write to theaddress pointer register to set up the relevant register address.
Therefore, block reads are not possible because there is no I2C
address pointer auto-increment except when reading back froma 16-bit register. If the address pointer register has previously
been set up with the address of the register that is going toreceive a read command, there is no need to repeat a write
operation to set up the register address again.

Reading back from any register first requires a single-byte write
operation to the address pointer register. This operation sets up
the address of the register that is going to be read from. In the
1

9

1

9

SCL

1

SDA

0

0

0

1

A1

A0

R/W

START BY
MASTER

P7

P6

P5

P4

P3

P2

P1

P0

ACK. BY
ADT7422

ACK. BY
ADT7422

FRAME 1SERIAL BUS ADDRESSBYTEFRAME 2ADDRESS POINTER REGISTER BYTE

1

9

1

9

SCL

0

0

1

0

A1

A0

R/W

D7

D6

ACK. BY
ADT7422

FRAME 3SERIAL BUS ADDRESS
BYTE

D5

D4

D3

D2

D1

FRAME 4DATA BYTE FROM CONFIGURATIONREGISTER

D0
NO ACK. BY STOP BY
MASTER MASTER
20961-015

1

SDA
REPEAT START
BY MASTER

Figure 18. Reading Back Data from the Configuration Register

9

1

9

1

SCL

SDA
1

0

START

0

0

1

A1

A0

ADT7410 DEVICE ADDRESS

R/W
ACK. BY
ADT7422

1

SR

A7

A6

A1

A0
ACK. BY
ADT7422REGISTER ADDRESS[A7:A0]

9

1

9

SCL

REPEAT
START

1

0

A1

A0

ADT7410 DEVICE ADDRESS

R/W
ACK. BY
ADT7422

D7

D6

D1

TEMPERATUREVALUE REGISTERMSB DATA

D0

D7

ACK. BY
MASTER

D6

D1

TEMPERATUREVALUE REGISTERLSB DATA

D0NO
ACK. BY
MASTERNOTES
1. A START CONDITION AT THE BEGINNING IS DEFINED AS A HIGH TO LOW TRANSITION ON SDA WHILE SCL REMAINS HIGH.
2. A STOP CONDITION AT THE END IS DEFINED AS A LOW TO HIGH TRANSITION ON SDA WHILE SCL REMAINS HIGH.
3. THE MASTER GENERATES THE NO ACKNOWLEDGE AT THE END OF THE READBACK TO SIGNAL THAT IT DOES NOT WANT ADDITIONAL DATA.
4. TEMPERATURE VALUE REGISTER MSB DATA AND TEMPERATURE VALUE REGISTER LSB DATA ARE ALWAYS SEPARATED BY A LOW ACK BIT.
5. THE R/W BIT IS SET TO A1 TO INDICATE A READBACK OPERATION.

Figure 19. Reading Back Data from the Temperature Value Register

Rev. 0 | Page 18 of 23

20961-0016

SDA

Data Sheet

ADT7422RESET

GENERAL CALL
2

To reset the ADT7422 without having to reset the entire I C bus,
an explicit reset command is provided. This command uses aparticular address pointer word as a command word to reset thedevice and upload all default settings. The ADT7422 does not
respond to (does not acknowledge) the I2C bus commands
while the default values upload for approximately 200 μs. Use
the following sequence to perform a reset:
1.
2.
3.
4.
5.
6.

Write to the ADT7422 using the appropriate address.
Read the acknowledge bit.
Set the register address to 0x2F.
Read the acknowledge bit.
Apply stop condition.
Wait 200 μs for the device to reset the registers to thedefault power-up settings.

When a master issues a slave address consisting of seven 0s withthe 8th bit (R/W bit) set to 0, the address is known as the generalcall address. The general call address is for addressing every device
connected to the I2C bus. The ADT7422 acknowledges this address
and reads in the following data byte.
If the second byte is 0x06, the ADT7422 resets completely anduploads all default values. The ADT7422 does not respond to(does not acknowledge) the I2C bus commands while thedefault values upload for approximately 200 μs.
The ADT7422 does not acknowledge any other general callcommands.

Rev. 0 | Page 19 of 23

ADT7422

Data Sheet

INT AND CT OUTPUTS
Comparator Mode

The INT pin and CT pin are open-drain outputs, and both
require a 10 kΩ pull-up resistor to VDD. The ADT7422 must be
fully powered up to VDD before reading the INT and CT data.

In comparator mode, the INT pin returns to inactive statuswhen the temperature drops below the THIGH − THYST limit orrises above the TLOW + THYST limit.

UNDERTEMPERATURE AND OVERTEMPERATURE
DETECTION

Placing the ADT7422 in shutdown mode does not reset the INT
state in comparator mode.

The INT pin and CT pin have two undertemperature/overtemperature modes: comparator mode and interrupt mode. The interrupt
mode is the default power-up overtemperature mode. The INT
output pin becomes active when the temperature is greater than
the temperature stored in the THIGH setpoint register or less than
the temperature stored in the TLOW setpoint register. How theINT pin reacts after this event depends on the overtemperaturemode selected.

Interrupt Mode
In interrupt mode, the INT pin goes inactive when any ADT7422
register is read. When the INT pin is reset, it only goes active
again when the temperature is either greater than the temperature
stored in the THIGH setpoint register, or less than the temperature
stored in the TLOW setpoint register.
Placing the ADT7422 in shutdown mode resets the INT pin ininterrupt mode.

Figure 20 shows the comparator and interrupt modes for events
exceeding the THIGH limit with both pin polarity settings. Figure 21
shows the comparator and interrupt modes for events exceeding
the TLOW limit with both pin polarity settings.
TEMPERATURE
82°C
81°C

THIGH

80°C
79°C
78°C
77°C
76°C

THIGH – THYST

75°C
74°C
73°C

INT PIN(COMPARATOR MODE)
POLARITY = ACTIVE LOW
INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE LOW

INT PIN(COMPARATOR MODE)
POLARITY = ACTIVE HIGH

TIME
READ

READ

READ

20961-017

INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE HIGH

Figure 20. INT Output Temperature Response Diagram for THIGH Overtemperature Events

Rev. 0 | Page 20 of 23

Data Sheet

ADT7422
TEMPERATURE
–13°C
–14°C
TLOW + THYST

–15°C
–16°C
–17°C
–18°C
–19°C

TLOW

–20°C
–21°C
–22°C

INT PIN(COMPARATOR MODE)
POLARITY = ACTIVE LOW
INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE LOW

INT PIN(COMPARATOR MODE)
POLARITY = ACTIVE HIGH

TIME
READ

READ

READ

20961-018

INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE HIGH

Figure 21. INT Output Temperature Response Diagram for TLOW Undertemperature Events

Rev. 0 | Page 21 of 23

ADT7422

Data SheetAPPLICATIONS INFORMATIONTHERMAL RESPONSE TIME

POWERING FROM A SWITCHING REGULATOR

Thermal response is a function of the thermal mass of thetemperature sensor and is heavily influenced by the mass of theobject the IC is mounted to. For example, a large PCB containing
large amounts of copper tracking can act as a large heat sink andslow the thermal response. For a faster thermal response, it isrecommended to mount the sensor on the smallest PCB possible.

Precision analog devices such as the ADT7422 require a wellfiltered power source. If the ADT7422 is powered from a switchingregulator, noise may be generated above 50 kHz that can affectthe temperature accuracy specifications. To prevent this issue, usean RC filter between the power supply and the ADT7422 VDD pin.
Carefully consider the value of the components used to ensure thatthe peak value of the supply noise is less than 1 mV. Mount the
RC filter as far away from the ADT7422 as possible to ensure thatthe thermal mass is kept as low as possible.

Figure 11 shows the typical response time of less than two seconds
to reach 63.2% of the temperature span. The temperature value
is read back as a 16-bit value through the digital interface. The
response time includes all delays incurred on the chip during
signal processing.

SUPPLY DECOUPLING
The ADT7422 must have a decoupling capacitor connected
between VDD and GND. Otherwise, incorrect temperature
readings are obtained. A 0.1 μF decoupling capacitor, such as ahigh frequency ceramic type, must be used and mounted as
close as possible to the VDD pin of the ADT7422.
If possible, power the ADT7422 directly from the system power
supply. This arrangement, shown in Figure 22, isolates theanalog section from the logic-switching transients. If a separate
power supply trace is not available, generous supply bypassing
still reduces supply line induced errors. Local supply bypassing
consisting of a 0.1 μF ceramic capacitor is critical for thetemperature accuracy specifications to be achieved.
TTL/CMOSLOGICCIRCUITSTEMPERATURE MEASUREMENT
The ADT7422 accurately measures and converts the temperature
at the surface of the semiconductor chip. Thermal paths run
through the leads, the exposed pad, and the plastic package.
When the ADT7422 is used to measure the temperature of anearby heat source, the thermal impedance between the heatsource and the ADT7422 must be considered because it impacts
the accuracy and thermal response of the measurement.
For air or surface temperature measurements, take care toisolate the package, leads, and exposed pad from ambient air
temperature. Use of a thermally conductive adhesive helps toachieve a more accurate surface temperature measurement.

QUICK GUIDE TO MEASURING TEMPERATURE
To measure temperature in continuous conversion mode
(default power-up mode), take the following steps:
1.

0.1µF

ADT7422POWER
SUPPLY

20961-019

2.

Figure 22. Use of Separate Traces to Reduce Power Supply Noise

3.
4.

Rev. 0 | Page 22 of 23

When the ADT7422 is powered up, read the device ID(Register Address 0x0B) to verify the setup. The ID reads
0xCB.
When consistent, consecutive readings are obtained from
Step 1, read the configuration register (Register Address 0x03),
TCRIT setpoint registers (Register Address 0x08 and Register
Address 0x09), THIGH setpoint registers (Register Address 0x04
and Register Address 0x05), and TLOW setpoint registers(Register Address 0x06 and Register Address 0x07).
Compare the values to the specified defaults in Table 7. If
all readings match, the interface is operational.
Write to the configuration register to set the ADT7422 to
the desired configuration.
Read the temperature value most significant byte register
followed by the temperature value least significant byte
register. Both registers produce a valid temperature
measurement.

Data Sheet

ADT7422OUTLINE DIMENSIONSDETAIL A(JEDEC 95)

PIN 1
INDICATOR
AREA

4.10
4.00 SQ
3.90

0.35
0.30
0.25
0.65
BSC

16

13

P IN 1IN D IC ATO R AR E A OP T IO N S(SEE DETAIL A)

12
1

EXPOSED
PAD
4

2.70
2.60 SQ
2.50

9

0.80
0.75
0.70

SIDE VIEW

PKG-004828

SEATING
PLANE

0.45
0.40
0.35

5

8

BOTTOM VIEW

0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF

0.20 MIN

FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONSSECTION OF THIS DATA SHEET.

COMPLIANT TO JEDEC STANDARDS MO-220-WGGC.

08-23-2018-C

TOP VIEW

Figure 23. 16-Lead Lead Frame Chip Scale Package [LFCSP]
4 mm × 4 mm Body and 0.75 mm Package Height(CP-16-17)
Dimensions shown in millimeters

ORDERING GUIDE
Model1
ADT7422CCPZ-RL7
1

Temperature Range−40°C to +125°C

Package Description
16-Lead Lead Frame Chip Scale Package [LFCSP]Z = RoHS Compliant Part.

©2020 Analog Devices, Inc. All rights reserved. Trademarks andregistered trademarks are the property of their respective owners.
D20961-1/20(0)Rev. 0 | Page 23 of 23

Package Option
CP-16-17