±0.25°C Accurate, 16-Bit Digital
I2C Temperature Sensor
ADT7420

Data SheetFEATURES

GENERAL DESCRIPTIONHigh performance
Temperature accuracy±0.20°C from −10°C to +85°C at 3.0 V±0.25°C from −20°C to +105°C from 2.7 V to 3.3 V
16-bit resolution: 0.0078°C
Ultralow temperature drift: 0.0073°C
NIST traceable or equivalent
Fast first temperature conversion on power-up of 6 ms
Easy implementation
No temperature calibration/correction required by user
No linearity correction required
Low power
Power-saving 1 sample per second (SPS) mode
700 µW typical at 3.3 V in normal mode
7 µW typical at 3.3 V in shutdown mode
Wide operating ranges
Temperature range: −40°C to +150°C
Voltage range: 2.7 V to 5.5 V
Programmable interrupts
Critical overtemperature interrupt
Overtemperature/undertemperature interrupt
I2C-compatible interface
16-lead, 4 mm × 4 mm LFCSP RoHS-compliant package

The ADT7420 is a high accuracy digital temperature sensor
offering breakthrough performance over a wide industrial range,
housed in a 4 mm × 4 mm LFCSP package. It contains an internalband gap reference, a temperature sensor, and a 16-bit ADC tomonitor and digitize the temperature to 0.0078°C resolution.
The ADC resolution, by default, is set to 13 bits (0.0625°C).
The ADC resolution is a user programmable mode that can bechanged through the serial interface.
The ADT7420 is guaranteed to operate over supply voltages from
2.7 V to 5.5 V. Operating at 3.3 V, the average supply current is typically 210 μA. The ADT7420 has a shutdown mode that powers
down the device and offers a shutdown current of typically 2.0 μA
at 3.3 V. The ADT7420 is rated for operation over the −40°C to+150°C temperature range.
Pin A0 and Pin A1 are available for address selection, giving the
ADT7420 four possible I2C addresses. The CT pin is an opendrain output that becomes active when the temperature exceeds
a programmable critical temperature limit. The INT pin is also
an open-drain output that becomes active when the temperature exceeds a programmable limit. The INT pin and CT pin
can operate in comparator and interrupt event modes.

PRODUCT HIGHLIGHTSAPPLICATIONS

1.
2.
3.
4.

RTD and thermistor replacement
Thermocouple cold junction compensation
Medical equipment
Industrial control and test
Food transportation and storage
Environmental monitoring and HVAC
Laser diode temperature control

5.

Ease of use, no calibration or correction required by the user.
Low power consumption.
Excellent long-term stability and reliability.
High accuracy for industrial, instrumentation, and medical
applications.
Packaged in a 16-lead, 4 mm × 4 mm LFCSP RoHScompliant package.

FUNCTIONAL BLOCK DIAGRAM

A0 3
A1 4

CONFIGURATIONREGISTERTEMPERATUREVALUE REGISTERINTERNAL
OSCILLATORTLOWREGISTERTCRITREGISTERINTERNAL
REFERENCE

THYST
REGISTER

THIGH
REGISTERTEMPERATURESENSORID
REGISTERSTATUSREGISTERSOFTWARERESET REGISTER

POINTERREGISTER

ADT7420

Σ-Δ
MODULATOR

THIGH

FILTER
LOGIC

TLOW

I2C INTERFACE

10

CT

9

INT

1

SCL

2

SDA

TCRIT

09013-001

VDD 12

11

GND

Figure 1.
Rev. 0Document Feedback

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or otherrights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700©2012 Analog Devices, Inc. All rights reserved.

Technical Support

www.analog.com

ADT7420

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

Temperature Value Registers .................................................... 13

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

Status Register ............................................................................. 14

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

Configuration Register .............................................................. 14

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

THIGH Setpoint Registers ............................................................. 15

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

TLOW Setpoint Registers.............................................................. 15

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

TCRIT Setpoint Registers.............................................................. 15

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

THYST Setpoint Register............................................................... 16

I C Timing Specifications ............................................................ 5

ID Register................................................................................... 16

Absolute Maximum Ratings ............................................................ 6

Serial Interface ................................................................................ 17

ESD Caution .................................................................................. 6

Serial Bus Address ...................................................................... 17

Pin Configuration and Function Descriptions ............................. 7

Writing Data ............................................................................... 18

Typical Performance Characteristics ............................................. 8

Reading Data ............................................................................... 19

Theory of Operation ...................................................................... 10

Reset ............................................................................................. 20

Circuit Information .................................................................... 10

General Call ................................................................................ 20

Converter Details........................................................................ 10

INT and CT Outputs...................................................................... 21

Normal Mode .............................................................................. 10

Undertemperature and Overtemperature Detection ............ 21

One-Shot Mode .......................................................................... 10

Applications Information .............................................................. 23

1 SPS Mode .................................................................................. 11

Thermal Response Time ........................................................... 23

Shutdown ..................................................................................... 11

Supply Decoupling ..................................................................... 23

Fault Queue ................................................................................. 11Powering from a Switching Regulator ..................................... 23

Temperature Data Format ......................................................... 12

Temperature Measurement ....................................................... 23

Temperature Conversion Formulas ......................................... 12

Quick Guide to Measuring Temperature ................................ 23

Registers ........................................................................................... 13

Outline Dimensions ....................................................................... 24

Address Pointer Register ........................................................... 13

Ordering Guide .......................................................................... 24

2

REVISION HISTORY
12/12—Revision 0: Initial Version

Rev. 0 | Page 2 of 24

Data Sheet

ADT7420

SPECIFICATIONSTA = −40°C to +125°C, VDD = 2.7 V to 5.5 V, unless otherwise noted.
Table 1.
Parameter
TEMPERATURE SENSOR AND ADC
Accuracy 1

Min

Typ

Max

Unit

Test Conditions/Comments

0.0017±0.20 2
±0.25
±0.31
±0.35
±0.50
±0.50 3
±0.66

−0.85
−1.0
13

°C
°C
°C
°C
°C
°C
°C
°C
°C
Bits

16

Bits

TA = −10°C to +85°C, VDD = 3.0 V
TA = −20°C to +105°C, VDD = 2.7 V to 3.3 V
TA = −40°C to +105°C, VDD = 3.0 V
TA = −40°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
TA = −10°C to +105°C, VDD = 4.5 V to 5.5 V
TA = −40°C to +125°C, VDD = 4.5 V to 5.5 V
TA = +150°C, VDD = 4.5 V to 5.5 V
TA = +150°C, VDD = 2.7 V to 3.3 V
Twos complement temperature value of thesign bit plus 12 ADC bits (power-up default
resolution)
Twos complement temperature value of thesign bit plus 15 ADC bits (Bit 7 = 1 in theconfiguration register)Temperature Resolution
13-Bit16-BitTemperature Conversion Time

0.06250.0078
240

°C
°C
ms

Fast Temperature Conversion Time
1 SPS Conversion Time
Temperature Hysteresis 4660±0.002ms
ms°C±0.0150.0073
0.1

°C
°C
°C/V

ADC Resolution

Repeatability 5
Drift 6
DC PSRR
DIGITAL OUTPUTS (CT, INT, SDA—OPEN DRAIN)High Output Leakage Current, IOH
Output Low Voltage, VOL
Output High Voltage, VOH
Output Capacitance, COUT
DIGITAL INPUTS (SCL, SDA, A0, A1)
Input Current
Input Low Voltage, VIL

5
0.4

µA
V
V
pF

CT and INT pins pulled up to 5.5 V
IOL = 3 mA at 5.5 V, IOL = 1 mA at 3.3 V±1
0.3 × VDD
0.4

µA
V
V
V
V
ns

VIN = 0 V to VDD
SCL and SDA only
A0 and A1 only
SCL and SDA only
A0 and A1 only
Input filtering suppresses noise spikes of lessthan 50 ns

10

pF

5.5

V

210

265

µA

At 5.5 V

250

300

µA

1 SPS Current
At 3.3 V
At 5.5 V

46
65

Input High Voltage, VIH

0.1

13-bit resolution (sign + 12-bit)
16-bit resolution (sign + 15-bit)
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 and backto 25°C
TA = 25°C
500 hour stress test at +150°C with VDD = 5.0 V
TA = 25°C

0.7 × VDD
2

0.7 × VDD
2

SCL, SDA Glitch Rejection
Pin Capacitance
POWER REQUIREMENTS
Supply Voltage
Supply Current
At 3.3 V

50
2
2.7

Rev. 0 | Page 3 of 24µAµA

Peak current while converting, I2C interface
inactive
Peak current while converting, I2C interface
inactive
VDD = 3.3 V, 1 SPS mode, TA = 25°C
VDD = 5.5 V, 1 SPS mode, TA = 25°C

ADT7420
Parameter
Shutdown Current
At 3.3 V
At 5.5 V
Power Dissipation Normal Mode
Power Dissipation 1 SPS

Data Sheet
Min

Typ

Max

Unit

Test Conditions/Comments

2.0
5.2
700
150

15
25

µA
µA
µW
µW

Supply current in shutdown mode
Supply current in shutdown mode
VDD = 3.3 V, normal mode at 25°C
Power dissipated for VDD = 3.3 V, TA = 25°C

Accuracy specification includes repeatability.
The equivalent 3 σ limits are ±0.15°C. This 3 σ specification is provided to enable comparison with other vendors who use these limits.
For higher accuracy at 5 V operation, contact Analog Devices, Inc.
4
Temperature Hysteresis does not include repeatability.
5
Based on a floating average of 10 readings.
6
Drift includes solder heat resistance and life time test performed as per JEDEC Standard JESD22-A108.
1
2
3

Rev. 0 | Page 4 of 24

Data Sheet

ADT7420I2C TIMING SPECIFICATIONSTA = −40°C to +150°C, VDD = 2.7 V to 5.5 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 INTERFACE1SCL Frequency
SCL High Pulse Width, tHIGH
SCL Low Pulse Width, tLOW
SCL, SDA Rise Time, tR
SCL, SDA Fall Time, tF
Hold Time (Start Condition), tHD:STA
Setup Time (Start Condition), tSU:STA
Data Setup Time, tSU:DAT
Setup Time (Stop Condition), tSU:STO
Data Hold Time, tHD:DAT (Master)Bus-Free Time (Between Stop and Start Condition), tBUF
Capacitive Load for Each Bus Line, CB
1

Min
0
0.6
1.3

Typ

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

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

Sample tested during initial release to ensure compliance.

Timing Diagram
tLOW

tR

tF

tHD:STASCLtHD:STAtHD:DATtHIGHtSU:STAtSU:DATtSU:STO

tBUF
P

S

S

Figure 2. Serial Interface Timing Diagram

Rev. 0 | Page 5 of 24

P

09013-002

SDA

ADT7420

Data Sheet

ABSOLUTE MAXIMUM RATINGS
Table 3.
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
ESD Rating (Human Body Model)
Operating Temperature Range1
Storage Temperature Range
Maximum Junction Temperature, TJMAX
16-Lead LFCSP (CP-16-17)
Power Dissipation2
Thermal Impedance4
θJA, Junction-to-Ambient (Still Air)
θJC, Junction-to-Case
IR Reflow Soldering
Peak Temperature (RoHS-Compliant
Package)Time at Peak TemperatureRamp-Up Rate
Ramp-Down Rate
Time from 25°C to 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
2.0 kV−40°C to +150°C−65°C to +160°C
150°C

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stressrating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affectdevice reliability.

ESD CAUTIONWMAX = (TJMAX − TA3)/θJA
37°C/W
33°C/W
220°C
260°C (+0°C/−5°C)
20 sec to 40 sec
3°C/sec maximum−6°C/sec maximum
8 minutes maximum

Sustained operation above 125°C results in a shorter product lifetime. For
more information, contact Analog Devices.
2
Values relate to package being used on a standard 2-layer PCB. This gives aworst-case θJA and θJC.
3
TA = ambient temperature.
4
Junction-to-case resistance is applicable to components featuring apreferential flow direction, for example, components mounted on a heatsink. Junction-to-ambient is more useful for air-cooled, PCB-mounted
components.
1Rev. 0 | Page 6 of 24

Data Sheet

ADT7420

14 NC

13 NC

16 NC

15 NC

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
17 EP
SCL 1
A0 3

ADT7420

11 GNDTOP VIEW

10 CT(Not to Scale)

9
NC 7

INT

NC 8

NC 5

NC 6

A1 4

NOTES
1. NC = NO CONNECT. THE NC PIN IS NOTBONDED TO THE DIE INTERNALLY.
2. TO ENSURE CORRECT OPERATION, THE
EXPOSED PAD SHOULD EITHER BE LEFTFLOATING OR CONNECTED TO GROUND.

09013-004

SDA 2

12 VDD

Figure 3. Pin Configuration

Table 4. Pin Function Descriptions
Pin No.
1

Mnemonic
SCL

2

SDA

3
4
5
6
7
8
9

A0
A1
NC
NC
NC
NC
INT

10

CT

11
12
13
14
15
16
17

GND
VDD
NC
NC
NC
NC
EP

Description
I2C Serial Clock Input. The serial clock is used to clock in and clock out data to and from any register of the ADT7420.
Open-drain configuration. A pull-up resistor is required, typically 10 kΩ.
I2C Serial Data Input/Output. Serial data to and from the part is provided on this pin. Open-drain configuration. A
pull-up resistor is required, typically 10 kΩ.
I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
I2C Serial Bus Address Selection Pin. Logic input. Connect to GND or VDD to set an I2C address.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
Overtemperature and Undertemperature Indicator. Logic output. Power-up default setting is as an active low
comparator interrupt. Open-drain configuration. A pull-up resistor is required, typically 10 kΩ.
Critical Overtemperature Indicator. Logic output. Power-up default polarity is active low. Open-drain configuration.
A pull-up resistor is required, typically 10 kΩ.
Analog and Digital Ground.
Positive Supply Voltage (2.7 V to 5.5 V). The supply should be decoupled with a 0.1 μF ceramic capacitor to ground.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
No Connect. The NC pin is not bonded to the die internally.
Exposed Pad. To ensure correct operation, the exposed pad should either be left floating or connected to ground.

Rev. 0 | Page 7 of 24

ADT7420

Data Sheet

TYPICAL PERFORMANCE CHARACTERISTICS
30

1.00

25

0.50

SHUTDOWN IDD (µA)

MAX ACCURACY LIMITS
0.25
0
–0.25
MAX ACCURACY LIMITS

20

15

10

5.5V
5.0V

–0.50
5

4.5V

–40

–20

80
60
20
40
TEMPERATURE (°C)

0

100

120

140

0
–100

09013-027

–1.00
–60

–50

0

50

100

150

200

TEMPERATURE (°C)

Figure 7. Shutdown Current vs. Temperature

Figure 4. Temperature Accuracy at 3 V
300

1.00
0.75

IDD CONTINUOUS CONVERSION250

MAX ACCURACY LIMITS
0.50
200

0.25
IDD (µA)

TEMPERATURE ERROR (°C)

3.3V
3.0V
2.7V

3.6V

–0.75

09013-032

TEMPERATURE ERROR (°C)

0.75

0
–0.25

150

100

–0.50

IDD 1SPS

MAX ACCURACY LIMITS

50

–40

–20

60
80
20
40
TEMPERATURE (°C)

0

100

120

140

0
2.5

09013-026

–1.00
–60

3.0

3.5

4.0

4.5

5.0

5.5

6.0

SUPPLY VOLTAGE (V)Figure 5. Temperature Accuracy at 5 V

09013-029–0.75

Figure 8. Average Operating Supply Current vs. Supply Voltage

8300

5.5V CONTINUOUS
CONVERSION

250

7
6

100

–50

0

4
3

5.5V 1SPS

2

3.0V 1SPS

1

50

0
–100

5

50

100

150

TEMPERATURE (°C)

200

0
2.5

3.0

3.5

4.0

4.5

5.0

5.5

SUPPLY VOLTAGE (V)Figure 9. Shutdown Current vs. Supply Voltage

Figure 6. Operating Supply Current vs. Temperature

Rev. 0 | Page 8 of 24

6.0

09013-210

150

09013-028

IDD (µA)

SHUTDOWN IDD (µA)

3.0V CONTINUOUS
CONVERSION

200

Data Sheet

ADT7420

140
125°C
120

85°C
80
IT TAKES LESS THAN
2 SECONDS TO REACH 63.2%
OF ITS TEMPERATURE SPAN

60

40
20
0
0

5

10

15
TIME (s)202509013-110

DUT TEMPERATURE (°C)

105°C
100

Figure 10. Thermal Response Time

Rev. 0 | Page 9 of 24

ADT7420

Data Sheet

THEORY OF OPERATIONCIRCUIT INFORMATIONNORMAL MODE

The ADT7420 is a high accuracy digital temperature sensor thatuses 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
digital modulator.

In normal mode (default power-up mode) the ADT7420 runs
an automatic conversion sequence. During this automatic conversion sequence, a conversion typically takes 240 ms to complete
and the ADT7420 is continuously converting. This means thatas soon as one temperature conversion is completed, anothertemperature conversion begins. Each temperature conversion
result is stored in the temperature value registers and is available
through the I2C interface. In continuous conversion mode, theread operation provides the most recent converted result.

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 sigma-delta (Σ-Δ) modulator,
also known as the charge balance type analog-to-digital converter. This type of converter utilizes time-domain oversampling
and a high accuracy comparator to deliver 16 bits of resolution
in an extremely compact circuit.

CONVERTER DETAILSThe Σ-Δ modulator consists of an input sampler, a summing
network, an integrator, a comparator, and a 1-bit DAC. Thisarchitecture creates a negative feedback loop and minimizes theintegrator output by changing the duty cycle of the comparator
output in response to input voltage changes. The comparator
samples the output of the integrator at a much higher rate than
the input sampling frequency. This oversampling spreads thequantization noise over a much wider band than that of the
input signal, improving overall noise performance andincreasing accuracy.

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 the measured
value exceeds these limits, the INT pin is activated; and if it exceeds
the TCRIT limit, the CT pin is activated. The INT and CT pins areprogrammable for polarity via the configuration register, and the
INT and CT pins are also programmable for interrupt mode via
the configuration register.
Setting Bit 6 to 0 and Bit 5 to 1 of the configuration register(Register Address 0x03) enables the one-shot mode. When
this mode is enabled, the ADT7420 immediately completes
a conversion and then goes into shutdown mode.

INTEGRATORCOMPARATORVOLTAGE REF
AND VPTAT

Wait for a minimum of 240 ms after writing to the operation
mode bits before reading back the temperature from the temperature value register. This time ensures that the ADT7420
has time to power up and complete a conversion.

1-BIT
DAC

13-BIT/
16-BIT

TEMPERATUREVALUEREGISTER

Figure 11. Σ-Δ Modulator

The ADT7420 can be configured to operate in any one of thefollowing four operating modes: normal, one-shot, 1 SPS, andshutdown.

09013-012

1-BIT
LPF DIGITALFILTER

The conversion clock for the part is generated internally.
No external clock is required except when reading fromand writing to the serial port.

ONE-SHOT MODEΣ-∆ MODULATOR

CLOCK
GENERATOR

On power-up, the first conversion is a fast conversion, taking
typically 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.

To obtain an updated temperature conversion, reset Bit 6 to 0
and Bit 5 to 1 in the configuration register (0x03).
The one-shot mode is useful when one of the circuit designpriorities is to reduce power consumption.

Rev. 0 | Page 10 of 24

Data Sheet

ADT7420CT and INT Operation in One-Shot Mode
See Figure 12 for more information on one-shot CT pin
operation for TCRIT overtemperature events when one of thelimits is exceeded. Note that in interrupt mode, a read fromany register resets the INT and CT pins.
For the INT pin in the comparator mode, if the temperature drops
below the THIGH – THYST value or goes above the TLOW + THYST
value, a write to the operation mode bits (Bit 5 and Bit 6 of theconfiguration register, Register Address 0x03) resets the INT pin.
For the CT pin in the comparator mode, if the temperaturedrops below the TCRIT – THYST value, a write to the operation
mode bits (Bit 6 = 0 and Bit 5 = 1 of the configuration register,
Register Address 0x03) resets the CT pin (see Figure 12).
Note that when using one-shot mode, ensure that the refresh
rate is appropriate to the application being used.

1 SPS MODE
In this mode, the part performs one measurement per second.
A conversion takes only 60 ms typically, and it remains in
the idle state for the remaining 940 ms period. This mode isenabled by writing 1 to Bit 6 and 0 to Bit 5 of the configuration
register (Register Address 0x03).

SHUTDOWN
The ADT7420 can be placed in shutdown mode by writing 1
to Bit 6 and 1 to Bit 5 of the configuration register (Register

Address 0x03), in which case the entire IC is shut down andno further conversions are initiated until the ADT7420 istaken out of shutdown mode. The ADT7420 can be takenout of shutdown mode by writing 0 to Bit 6 and 0 to Bit 5 inthe configuration register (Register Address 0x03). The
ADT7420 typically takes 1 ms (with a 0.1 µF decoupling
capacitor) to come out of shutdown mode. The conversion
result from the last conversion prior to shutdown can still beread from the ADT7420 even when it is in shutdown mode.
When the part is taken out of shutdown mode, the internal
clock is started and a conversion is initiated.

FAULT QUEUE
Bit 0 and Bit 1 of the configuration register (Register Address0x03) are used to set up a fault queue. The queue can facilitate up
to four fault events to prevent false tripping of the INT and CT pins
when the ADT7420 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, then four consecutive temperature
conversions must occur with each result exceeding a temperature
limit in any of the limit registers before the INT and CT pins areactivated. If two consecutive temperature conversions exceed atemperature limit and the third conversion does not, the fault
count is reset back to zero.

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 THE CT PIN GOING ACTIVE. THIS IS DUE TO THE
CONVERSION TIME. THE DELAY IS 60ms IN THE CASE OF A ONE-SHOT CONVERSION.

Figure 12. One-Shot CT Pin

Rev. 0 | Page 11 of 24

09013-013

WRITE TO
BIT 5 AND BIT 6 OF
CONFIGURATIONREGISTER.*ADT7420

Data SheetTEMPERATURE 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 ADC can theoretically measure atemperature range of 255°C, but the ADT7420 is guaranteed tomeasure a low value temperature limit of −40°C to a high value
temperature limit of +150°C. The temperature measurement
result is stored in the 16-bit temperature value register and iscompared with the high temperature limits stored in the TCRIT
setpoint register and the THIGH setpoint register. It is also compared with the low temperature limit stored in the TLOW setpoint
register.

16-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/128

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, Bit 0 to Bit 2, on
power-up, are not part of the temperature conversion result andare flag bits for TCRIT, THIGH, and TLOW. Table 5 shows the 13-bit
temperature data format without Bit 0 to Bit 2.
The number of bits in the temperature data-word can be extended
to 16 bits, twos complement, by setting Bit 7 to 1 in the configuration register (Register Address 0x03). When using a 16-bit
temperature data value, Bit 0 to Bit 2 are not used as flag bits
and are, instead, the LSB bits of the temperature value. The poweron default setting has a 13-bit temperature data value.
Reading back the temperature from the temperature value register
requires a 2-byte read. Designers that use a 9-bit temperature
data format can still use the ADT7420 by ignoring the last four
LSBs of the 13-bit temperature value. These four LSBs are Bit 6
to Bit 3 in Table 5.
Table 5. 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 (Hex)
0x1D800x1E700x1FFF
0x000
0x001
0x190
0x690
0x7D0
0x960

Negative Temperature = (ADC Code (dec) – 65,536)/128
where ADC Code uses all 16 bits of the data byte, including thesign bit.
Negative Temperature = (ADC Code (dec) – 32,768)/128
where Bit 15 (sign bit) is removed from the ADC code.

13-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/16
Negative Temperature = (ADC Code (dec) − 8192)/16
where ADC Code uses the first 13 MSBs of the data byte,
including the sign bit.
Negative Temperature = (ADC Code (dec) – 4096)/16
where Bit 15 (sign bit) is removed from the ADC code.

10-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)/2
Negative Temperature = (ADC Code (dec) − 1024)/2
where ADC Code uses all 10 bits of the data byte, including thesign bit.
Negative Temperature = (ADC Code (dec) − 512)/2
where Bit 9 (sign bit) is removed from the ADC code.

9-Bit Temperature Data Format
Positive Temperature = ADC Code (dec)
Negative Temperature = ADC Code (dec) − 512
where ADC Code uses all nine bits of the data byte, including
the sign bit.
Negative Temperature = ADC Code (dec) − 256
where Bit 8 (sign bit) is removed from the ADC code.

Rev. 0 | Page 12 of 24

Data Sheet

ADT7420REGISTERSThe ADT7420 contains 14 registers:

ADDRESS POINTER REGISTER

•
•
•
•
•
•

This register is always the first register written to during a write
to the ADT7420. It should be set to the address of the register
to which the write or read transaction is intended. Table 7
shows the register address of each register on the ADT7420.
The default value of the address pointer register is 0x00.

Nine temperature registers
A status register
An ID register
A configuration register
An address pointer register
A software reset

Table 7. Address Pointer RegisterAll registers are eight bits wide. The temperature value registers,
the status register, and the ID register are read-only. The software
reset is a write-only register. On power-up, the address pointerregister is loaded with 0x00 and points to the temperature value
most significant byte register (Register Address 0x00).
Table 6. ADT7420 Registers
Register
Address
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
0x2F

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 setpointID
Software reset

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

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 beread in two separate 1-byte reads or in a single 2-byte read. For a
2-byte read, only the address of the most significant byte must be
loaded into the address pointer register. After the most significant byte is read, the address pointer is auto-incremented so thatthe least significant byte can read within the same transaction.
Bit 0 to Bit 2 are event alarm flags for TLOW, THIGH, and TCRIT. When
the ADC is configured to convert the temperature to a 16-bit
digital value, then Bit 0 to Bit 2 are no longer used as flag bits
and are instead used as the LSBs for the extended digital value.

Table 8. Temperature Value MSB 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 9. Temperature Value LSB 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[7] = 0 (13-bit
resolution). When the temperature value is below TLOW, this bit it set to 1.
Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
Flags a THIGH event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value is above THIGH, this bit it set to 1.
Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
Flags a TCRIT event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value exceeds TCRIT, this bit it set to 1.
Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
Temperature value in twos complement format.

Rev. 0 | Page 13 of 24

ADT7420

Data SheetSTATUS REGISTERCONFIGURATION REGISTER

This 8-bit read-only register reflects the status of the overtemperature and undertemperature interrupts that can cause the CT and
INT pins to go active. It 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 thetemperature value returns within the temperature limits, including
hysteresis. The RDY bit is reset after a read from the temperature
value register. In one-shot and 1 SPS modes, the RDY bit is reset
after a write to the operation mode bits.

This 8-bit read/write register stores various configuration modes
for the ADT7420, including shutdown, overtemperature andundertemperature interrupts, one-shot, continuous conversion,interrupt pins polarity, and overtemperature fault queues.

Table 10. 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.

Table 11. 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 and CT pins. 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 ADT7420.
00 = continuous conversion (default). When one conversion is finished, the ADT7420 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 14 of 24

Data Sheet

ADT7420

THIGH SETPOINT REGISTERS
The THIGH setpoint MSB and THIGH setpoint LSB registers store
the overtemperature limit value. An overtemperature event
occurs when the temperature 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 MSB being
the temperature sign bit.
When reading from this register, the eight most significant bits
(Bit 15 to Bit 8) are read first from Register Address 0x04 andthen the eight least significant bits (Bit 7 to Bit 0) are read from
Register Address 0x05 (THIGH setpoint LSB). Only Register
Address 0x04 (THIGH setpoint MSB) needs to be loaded into
the address pointer register because the address pointer autoincrements to Register Address 0x05 (THIGH setpoint LSB).
The default setting for the THIGH setpoint is 64°C.

TLOW SETPOINT REGISTERS
The TLOW setpoint MSB and TLOW setpoint LSB registers store
the undertemperature limit value. An undertemperature event
occurs when the temperature value stored in the temperature
value register is less than 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.

When reading from this register, the eight most significant bits
(Bit 15 to Bit 8) are read first from Register Address 0x06 andthen the eight least significant bits (Bit 7 to Bit 0) are read from
Register Address 0x07. Only Register Address 0x06 (TLOW setpoint
MSB) needs to be loaded into the address pointer register because
the address pointer auto-increments to Register Address 0x07
(TLOW setpoint LSB).
The default setting for the TLOW setpoint is 10°C.

TCRIT SETPOINT REGISTERS
The TCRIT setpoint MSB and TCRIT setpoint LSB registers store
the critical overtemperature limit value. A critical overtemperature event occurs when the temperature value stored in thetemperature value register exceeds the value stored in thisregister. 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.
When reading from this register, the eight most significant bits
(Bit 15 to Bit 8) are read first from Register Address 0x08 (TCRIT
setpoint MSB) and then the eight least significant bits (Bit 7 toBit 0) are read from Register Address 0x09 (TCRIT setpoint LSB).
Only Register Address 0x08 (TCRIT setpoint MSB) needs to beloaded into the address pointer register because the address pointerauto-increments to Register Address 0x09 (TCRIT setpoint LSB).
The default setting for the TCRIT limit is 147°C.

Table 12. THIGH Setpoint MSB Register (Register Address 0x04)
Bit

Default Value

Type

Name

Description[15:8]

0x20

R/W

THIGH MSB

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

Table 13. THIGH Setpoint LSB Register (Register Address 0x05)
Bit

Default Value

[7:0]

0x00

Type

Name

Description

R/W

THIGH LSB

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

Table 14. TLOW Setpoint MSB Register (Register Address 0x06)
Bit

Default Value

Type

Name

Description[15:8]0x05

R/W

TLOW MSB

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

Table 15. TLOW Setpoint LSB Register (Register Address 0x07)
Bit

Default Value

Type

Name

Description

[7:0]

0x00

R/W

TLOW LSB

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

Table 16. TCRIT Setpoint MSB Register (Register Address 0x08)
Bit

Default Value

Type

Name

Description[15:8]

0x49

R/W

TCRIT MSB

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

Table 17. TCRIT Setpoint LSB Register (Register Address 0x09)
Bit

Default Value

Type

Name

Description

[7:0]

0x80

R/W

TCRIT LSB

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

Rev. 0 | Page 15 of 24

ADT7420

Data Sheet

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 four LSBs. Increments are possible in steps of 1°C from
0°C to 15°C. The value in this register is subtracted from the
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 18. 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

N/A

Not used.

Table 19. 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 16 of 24

Data Sheet

ADT7420SERIAL INTERFACE
PULL-UP
VDD

VDD
VDD

10kΩ

10kΩ

ADT7420CT
INT

TO INTERRUPT PIN
ON MICROCONTROLLER

A0
A1

PULL-UP
VDD
10kΩ

10kΩ

0.1µF

SCL
SDA
09013-014

PULL-UP
VDD

GND

Figure 13. Typical I2C Interface Connection

Control of the ADT7420 is carried out via the I2C-compatible
serial interface. The ADT7420 is connected to this bus as a slave
and is under the control of a master device.

2.

Figure 13 shows a typical I2C interface connection.

SERIAL BUS ADDRESS
Like most I2C-compatible devices, the ADT7420 has a 7-bit
serial address. The five MSBs of this address for the ADT7420
are hardwired internally to 10010. Pin A1 and Pin A0 set the
two LSBs. These pins can be configured two ways, low andhigh, to give four different address options. Table 20 shows
the different bus address options available. The recommended
pull-up resistor value on the SDA and SCL lines is 10 kΩ.
Table 20. I2C Bus Address Options
A6
1
1
1
1

A5
0
0
0
0

A4
0
0
0
0

Binary
A3
1
1
1
1

A2
0
0
0
0

3.

4.
A1
0
0
1
1

A0
0
1
0
1

Hex
0x48
0x49
0x4A
0x4B

The serial bus protocol operates as follows:1.

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

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 a 0, the master
writes to the slave device. If the R/W bit is a 1, the masterreads from the slave device.
Data is sent over the serial bus in sequences of nine clock
pulses, eight bits of data followed by an acknowledge bitfrom the receiver of data. Transitions on the data line mustoccur during the low period of the clock signal and remain
stable during the high period as a low-to-high transition when
the clock 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 thedata line high during the 10th clock pulse to assert a stop
condition. In read mode, the master device pulls the dataline high during the low period before the ninth clock
pulse. This is known as a no acknowledge. The mastertakes the data line low during the low period before the10th clock pulse, then high during the 10th clock pulse toassert a stop condition.

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

Rev. 0 | Page 17 of 24

ADT7420

Data Sheet
For the THIGH setpoint, TLOW setpoint, and TCRIT setpoint
registers, it is possible to write to both the MSB and the LSB
registers in the same write transaction. Writing two bytes ofdata to these registers requires the serial bus address, the dataregister address of the MSB register written to the address
pointer register, followed by the two data bytes written to
the selected data register. This is shown in Figure 15.

WRITING DATA
It is possible to write either a single byte of data or two bytes to
the ADT7420, depending on which registers are to be written.
Writing a single byte of data requires the serial bus address, thedata register address written to the address pointer register,followed by the data byte written to the selected data register.
This is shown in Figure 14.

If more than the required number of data bytes is written to aregister, the register ignores these extra data bytes. To write toa different register, a start or repeated start is required.

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
ADT7420

ACK. BY
ADT7420

FRAME 1SERIAL BUS ADDRESS BYTE

FRAME 2ADDRESS POINTER REGISTER BYTE
19SCL (CONTINUED)

D7

D6

D5

D4

D3

D2

D1

D0
ACK. BY
ADT7420

STOP BY
MASTERFRAME 3DATA BYTE

09013-016

SDA (CONTINUED)

Figure 14. 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
ADT7420

ACK. BY
ADT7420

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 15. Writing to a Register Followed by Two Bytes of Data

Rev. 0 | Page 18 of 24

D1

D0
ACK. BY
ADT7420

ACK. BY
ADT7420

STOP BY
MASTER

09013-017

SDA (CONTINUED)

Data Sheet

ADT7420
the register that is going to be read from. In the case of reading
back from the 2-byte registers, the address pointer automaticallyincrements from the MSB register address to the LSB register
address.

READING DATA
Reading data from the ADT7420 is done in a single data byte
operation for the configuration register, the status register,
the THYST setpoint register, and the ID register. A two data byte
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 an 8-bit register
similar to the configuration register is shown in Figure 16.
Reading back the contents of the temperature value register
is shown in Figure 17.

To read from another register, execute another write to theaddress pointer register to set up the relevant register address.
Thus, block reads are not possible, that is, there is no I2C address
pointer auto-increment except when reading back from a 16-bit
register. If the address pointer register has previously been set
up with the address of the register that is going to receive a readcommand, 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 to set up the address of
9

1

1

9

SCL

1

SDA

0

0

0

1

A1

A0

R/W

P7

P6

P5

P4

P3

P2

P1

P0

ACK. BY
ADT7420

START BY
MASTER

ACK. BY
ADT7420
FRAME 2ADDRESS POINTER REGISTER BYTE

FRAME 1SERIAL BUS ADDRESS
BYTE
9

1

1

9

SCL

0

0

1

0

A1

A0

R/W

D7

D6

ACK. BY
ADT7420

FRAME 3SERIAL BUS ADDRESS
BYTE

D5

D4

D3

D2

D1

FRAME 4DATA BYTE FROM CONFIGURATIONREGISTER

D0
NO ACK. BY STOP BY
MASTER MASTER
09013-018

1

SDA
REPEAT START
BY MASTER

Figure 16. Reading Back Data from the Configuration Register

9

1

9

1

SCL

SDA
1

0

START

0

0

1

A1

A0

ADT7410 DEVICE ADDRESSACK. BY
ADT7420

1

SR

A7

R/W

A6

A1

A0
ACK. BY
ADT7420REGISTER ADDRESS[A7:A0]

9

1

9

SCL

1
REPEAT
START

0

A1

A0

ADT7410 DEVICE ADDRESS

R/W
ACK. BY
ADT7420

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 VALIUE 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 17. Reading Back Data from the Temperature Value Register

Rev. 0 | Page 19 of 24

09013-023

SDA

ADT7420

Data SheetRESET

GENERAL CALL

To reset the ADT7420 without having to reset the entire I C bus,
an explicit reset command is provided. This uses a particularaddress pointer word as a command word to reset the part andupload all default settings. The ADT7420 does not respond to(does not acknowledge) I2C bus commands while the default
values upload for approximately 200 µs. Use the following
sequence to perform a reset:
2

1.
2.
3.
4.
5.
6.

Write to the ADT7420 using the appropriate address.
Get acknowledge.
Set the register address to 0x2F.
Get acknowledge.
Apply stop condition.
Wait 200 µs for the part to reset its registers to the default
power-up settings.

When a master issues a slave address consisting of seven 0s withthe eighth bit (R/W bit) set to 0, this is known as the general calladdress. The general call address is for addressing every device
connected to the I2C bus. The ADT7420 acknowledges thisaddress and reads in the following data byte.
If the second byte is 0x06, the ADT7420 is reset, completely
uploading all default values. The ADT7420 does not respondto the I2C bus commands (do not acknowledge) while thedefault values upload for approximately 200 µs.
The ADT7420 does not acknowledge any other general callcommands.

Rev. 0 | Page 20 of 24

Data Sheet

ADT7420

INT AND CT OUTPUTS
Comparator Mode

The INT and CT pins are open-drain outputs, and both pins
require a 10 kΩ pull-up resistor to VDD. The ADT7420 mustbe fully powered up to VDD before reading INT and CT data.

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

UNDERTEMPERATURE AND OVERTEMPERATURE
DETECTION

Putting the ADT7420 into shutdown mode does not reset the
INT state in comparator mode.

The INT and CT pins 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 thispin reacts after this event depends on the overtemperature mode
selected.

Interrupt Mode
In interrupt mode, the INT pin goes inactive when any ADT7420
register is read. Once the INT pin is reset, it goes active again
only 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.
Placing the ADT7420 into shutdown mode resets the INT pinin the interrupt mode.

Figure 18 illustrates the comparator and interrupt modes forevents exceeding the THIGH limit with both pin polarity settings.
Figure 19 illustrates the comparator and interrupt modes forevents 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

09013-020

INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE HIGH

Figure 18. INT Output Temperature Response Diagram for THIGH Overtemperature Events

Rev. 0 | Page 21 of 24

ADT7420

Data SheetTEMPERATURE
–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

09013-021

INT PIN(INTERRUPT MODE)
POLARITY = ACTIVE HIGH

Figure 19. INT Output Temperature Response Diagram for TLOW Undertemperature Events

Rev. 0 | Page 22 of 24

Data Sheet

ADT7420APPLICATIONS INFORMATIONTHERMAL RESPONSE TIME

POWERING FROM A SWITCHING REGULATOR

Thermal response is a function of the thermal mass of thetemperature sensor, but it is also heavily influenced by the massof the object the IC is mounted to. For example, a large PCB
containing large amounts of copper tracking can act as a large
heat sink and slow the thermal response. For a faster thermal
response, it is recommended to mount the sensor on as small a
PCB as possible.

Precision analog devices, such as the ADT7420 require a wellfiltered power source. If the ADT7420 is powered from aswitching regulator, noise may be generated above 50 kHz that
may affect the temperature accuracy specifications. To prevent
this, an RC filter should be used between the power supply and
ADT7420 VDD. The value of the components used should be
carefully considered to ensure that the peak value of the supply
noise is less than 1 mV. The RC filter should be mounted as far
away as possible from the ADT7420 to ensure that the thermal
mass is kept as low as possible.

Figure 10 shows the typical response time of less than two
seconds to reach 63.2% of its temperature span. The temperature value is read back as a 16-bit value through the digitalinterface. The response time includes all delays incurred onchip during signal processing.

TEMPERATURE MEASUREMENT

SUPPLY DECOUPLING
The ADT7420 must have a decoupling capacitor connected
between VDD and GND; otherwise, incorrect temperature
readings will be obtained. A 0.1 µF decoupling capacitor such asa high frequency ceramic type must be used and mounted as
close as possible to the VDD pin of the ADT7420.
If possible, the ADT7420 should be powered directly from thesystem power supply. This arrangement, shown in Figure 20,
isolates the analog section from the logic-switching transients.
Even if a separate power supply trace is not available, generous
supply bypassing reduces supply-line induced errors. Local
supply bypassing consisting of a 0.1 µF ceramic capacitor is
critical for the temperature accuracy specifications to beachieved.

0.1µF

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 can help
to achieve a more accurate surface temperature measurement.

QUICK GUIDE TO MEASURING TEMPERATURE
The following is a quick guide for measuring temperature incontinuous conversion mode (default power-up mode). Execute
each step sequentially.

ADT7420POWER
SUPPLY

1.

After powering up the ADT7420, verify the setup byreading the device ID (Register Address 0x0B). It should
read 0xCB.

2.

After consistent consecutive readings are obtained from
Step 1, proceed to read the configuration register (0x03),
TCRIT (0x08, 0x09), THIGH (0x04, 0x05), and TLOW (0x06,
0x07) registers. Compare to the specified defaults in Table 6.
If all the readings match, the interface is operational.

3.

Write to the configuration register to set the ADT7420 tothe desired configuration.

4.

Read the temperature value MSB register, followed by
the temperature value LSB register. Both registers should
produce a valid temperature measurement.

09013-022

TTL/CMOSLOGICCIRCUITSThe ADT7420 accurately measures and converts the temperature at the surface of its own semiconductor chip. Thermal
paths run through the leads, the exposed pad, as well as theplastic package. When the ADT7420 is used to measure thetemperature of a nearby heat source, the thermal impedance
between the heat source and the ADT7420 must be considered
because this impacts the accuracy and thermal response of themeasurement.

Figure 20. Use of Separate Traces to Reduce Power Supply Noise

Rev. 0 | Page 23 of 24

ADT7420

Data SheetOUTLINE DIMENSIONSPIN 1
INDICATOR

4.10
4.00 SQ
3.90

0.35
0.30
0.25
0.65
BSC

16

13

PIN 1
INDICATOR

12
1EXPOSED
PAD

4

2.70
2.60 SQ
2.50

9

0.80
0.75
0.70

0.25 MIN

BOTTOM VIEW

0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REFSEATING
PLANE

5FOR 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.

012909-B

0.45
0.40
0.35

TOP VIEW

8

Figure 21. 16-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
4 mm × 4 mm Body, Very Thin Quad
(CP-16-17)
Dimensions shown in millimeters

ORDERING GUIDE
Model1
ADT7420UCPZ-R2
ADT7420UCPZ-RL7
EVAL-ADT7X20EBZ
1

Operating Temperature Range−40°C to +150°C−40°C to +150°C

Package Description
16-lead LFCSP_WQ
16-lead LFCSP_WQ
Evaluation Board

Z = RoHS Compliant Part.

I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).

©2012 Analog Devices, Inc. All rights reserved. Trademarks andregistered trademarks are the property of their respective owners.
D09013-0-12/12(0)Rev. 0 | Page 24 of 24

Package Option
CP-16-17
CP-16-17