Design
Resources

Tools
and Models

SupportClick here to ask an associate for production status of specific part numbers.

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface
General Description

The MAX6627/MAX6628 precise digital temperature
sensors report the temperature of a remote sensor. The
remote sensor is a diode-connected transistor, typicallya low-cost, easily mounted 2N3904 NPN type that
replaces conventional thermistors or thermocouples. The
devices can also measure the die temperature of otherICs, such as microprocessors (µPs) or microcontrollers(µCs) that contain an on-chip, diode-connected transistor.
Remote accuracy is ±1°C when the temperature of the remote
diode is between 0°C and +125°C and the temperature of thedevices is +30°C. The temperature is converted to a 12-bit +sign word with 0.0625°C resolution. The architecture of thedevice is capable of interpreting data as high as +145°C fromthe remote sensor. The MAX6627/MAX6628 temperature
should never exceed +125°C.
These sensors are 3-wire serial interface SPI-compatible,
allowing the MAX6627/MAX6628 to be readily connected
to a variety of µCs. The MAX6627/MAX6628 are readonly devices, simplifying their use in systems where only
temperature data is required.
Two conversion rates are available, one that continuously
converts data every 0.5s (MAX6627), and one that converts
data every 8s (MAX6628). The slower version provides
minimal power consumption under all operating conditions(30µA, typ). Either device can be read at any time andprovide the data from the last conversion.

Benefits and Features● Accuracy• ±1°C (max) from 0°C ≤ TRJ ≤ +125°C, TA = +30°C• ±2.4°C (max) from -55°C ≤ TRJ ≤ +100°C,
0°C ≤ TA ≤ +70°C● 12-Bit + Sign, 0.0625°C Resolution● Low Power Consumption• 30μA (typ) (MAX6628)• 200μA (typ) (MAX6627)● Operating Temperature Range (-55°C to +125°C)● Measurement Temperature Range, Remote Junction(-55°C to +145°C)● 0.5s (MAX6627) or 8s (MAX6628) Conversion Rate
● SPI-Compatible Interface● +3.0V to +5.5V Supply Range● 8-Pin SOT23 and TDFN Packages● Lead(Pb)-Free Version Available (TDFN Package)
Ordering Information appears at end of data sheet.

Typical Operating Circuit+ 3V TO + 5.5V
0.1µF

Both devices operate with supply voltages between+3.0V and +5.5V, are specified between -55°C and+125°C, and come in space-saving 8-pin SOT23 andlead-free TDFN packages.

VCC

MAX6627
MAX6628

Applications
●
●
●
●

GND

SDO

Hard Disk Drive
Smart Battery Packs
Industrial Control Systems
Notebooks, PCs

DXP
2200pF

CS

µC

DXN
SCK

19-2032; Rev 9; 1/21

© 2021 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
One Analog Way, Wilmington, MA 01887 U.S.A.

|

Tel: 781.329.4700|© 2021 Analog Devices, Inc. All rights reserved.

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Absolute Maximum Ratings(All voltages referenced to GND.)
VCC...........................................................................-0.3V to +6V
SDO, SCK, DXP, CS................................. -0.3V to (VCC + 0.3V)
DXN.......................................................................-0.3V to +0.8V
SDO Pin Current Range...................................... -1mA to +50mA
Current Into All Other Pins..................................................10mA
ESD Protection (Human Body Model).............................±2000V

Continuous Power Dissipation (TA = +70°C)
SOT23 (derate 9.7mW/°C above +70°C).....................777mW
TDFN (derate 18.5mW/°C above +70°C)................1481.5mW
Operating Temperature Range.......................... -55°C to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65°C to +150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°C

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at theseor any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affectdevice reliability.

Electrical Characteristics(3.0V ≤ VCC ≤ 5.5V, -55°C ≤ TA ≤ +125°C, unless otherwise noted. Typical values are at TA = +25°C, VCC = +3.3V, unless otherwise
noted.)PARAMETERSYMBOL

CONDITIONS

MIN

TYP

MAX

0°C ≤ TRJ ≤ +125°C, TA = +30°C,
VCC = +3.3V

-1.0

±0.5

±1

-55°C ≤ TRJ ≤ +100°C, 0°C ≤ TA ≤ +70°C,
VCC = +3.3V

-2.4

+2.4

-55°C ≤ TRJ ≤ +145°C, 0°C ≤ TA ≤ +70°C,
VCC = +3.3V

-4.5

+4.5

-55°C ≤ TRJ ≤ +125°C, -55°C ≤ TA ≤+125°C,VCC = +3.3V

-5.5

+5.5

UNITS

TEMPERATURE

Accuracy (Note 1)°C

Power-Supply Sensitivity

0.25

Resolution

0.0625Time Between Conversion
StartsConversion TimetSAMPLEMAX6627

0.5

MAX6628

8
250

0.7

°C/V
°C
s

tCONV

180

320

ms

Supply Voltage Range

VCC

3.0

5.5

V

ISDO

Shutdown, VCC = +0.8V

5

Supply Current, SCK Idle

IIDLE

ADC idle, CS = low

20

ICONV

ADC converting

360

600

MAX6627

200

400

MAX662830

50

VCC, falling edge

1.6

POWER SUPPLY

Average Operating Current
Power-On Reset (POR)
ThresholdCurrent Sourcing for Diodewww.analog.com

ICC

µA

µA
V

High level

80

100

120

Low level

8

10

12

µA

Analog Devices │ 2

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Electrical Characteristics (continued)(3.0V ≤ VCC ≤ 5.5V, -55°C ≤ TA ≤ +125°C, unless otherwise noted. Typical values are at TA = +25°C, VCC = +3.3V, unless otherwise
noted.)PARAMETERSYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

0.3 x
VCC

V

LOGIC INPUTS (CS, SCK)
Logic Input Low Voltage

VIL

Logic Input High Voltage

VIH

Input Leakage Current

ILEAK

VCS = VSCK = GND or VCC

1

Output Low Voltage

VOL

ISINK = 1.6mA

0.4

Output High Voltage

VOH

ISOURCE = 1.6mA

0.7 x
VCC

V
µA

LOGIC OUTPUTS (SDO)
VCC 0.4

V

TIMING CHARACTERISTICS (Note 2, Figure 2)
Serial-Clock Frequency

fSCL

5

MHz

SCK Pulse Width High

tCH

100

ns

SCK Pulse Width Low

tCL

100

ns

CS Fall to SCK RisetCSS

CLOAD = 10pF

80

ns

CS Fall to Output Enable

tDV

CLOAD = 10pF

80

ns

CS Rise to Output DisabletTR

CLOAD = 10pF50ns

SCK Fall to Output Data ValidtDO

CLOAD = 10pF

80

ns

Note 1: TRJ is the temperature of the remote junction.
Note 2: Serial timing characteristics guaranteed by design.

www.analog.com

Analog Devices │ 3

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Typical Operating Characteristics(VCC = +3.3V, TA = +25°C, unless otherwise noted.)

MAX6627

150
100

MAX662850

TA = +25°C

1

MAX6627/8 toc02

TA = +70°C

0TA = 0°C-1-2

MAX6627
3.5

4.0

4.5

5.0

5.5

-5

20

45

70

95

2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6

120 145-55 -30

-5

20

45

70

95

120 145

SUPPLY VOLTAGE (V)TEMPERATURE (°C)

TEMPERATURE (°C)

TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCYRESPONSE TO THERMAL SHOCKTEMPERATURE ERROR
vs. DXP/DXN CAPACITANCE

86

VIN = 250mVp-p

4

100
75
50
25

2

10

100

1k

10k

100k

1M

FREQUENCY (Hz)www.analog.com

10M 100M

0

-2

0

2

4

6
TIME (s)

8

10

12

14

5

MAX6627/8 toc06

125

TEMPERATURE ERROR (°C)

VIN = SQUARE WAVEAPPLIED TO VCC WITH NO
0.1µF CAPACITOR

100-55 -30

MAX6627/8 toc05

12

3.0

-3

TEMPERATURE (°C)

0

TEMPERATURE ERROR (°C)

2

POWER-ON-RESET THRESHOLD
vs. TEMPERATURE

2.6
POWER-ON-RESET THRESHOLD (V)200

TEMPERATURE ERROR (°C)

MAX6627/8 toc01

250

3

MAX6627/8 toc04

AVERAGE OPERATING CURRENT (µA)

300

TEMPERATURE ERROR vs. TEMPERATURE

MAX6627/8 toc03

AVERAGE OPERATING CURRENT
vs. SUPPLY VOLTAGE

4
3
2
1
0

0

5000

10,00015,00020,000CAPACITANCE (pF)

Analog Devices │ 4

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Pin Configurations
TOP VIEW
GND

1

8

N.C.

DXN

2

7

SDO

DXP

3

6

CS

VCC 4

5

SCK

MAX6627

N.C.

SDO

CS

SCK

8

7

6

5

MAX6627
MAX6628
EP

+

SOT23

2

3

4

GND DXN

1

DXP

VCC

TDFN

Pin Description
PIN

NAME

1

GND

2

DXN

3

DXP

4
5

VCC
SCK

6

CS

Chip-Select Input. Pulling CS low initiates an idle state, but the SPI interface is still enabled. A rising-edgeof CS initiates the next conversion.

7

SDO

SPI Data Output

8

N.C.

No Connect. Internally not connected. Can be connected to GND for improved thermal conductivity.

—

EP

Exposed Pad. Internally connected to GND. Connect to a large ground plane to maximize thermal
performance. Not intended as an electrical connection point.

www.analog.com

FUNCTION
GroundCombined Current Sink and ADC Negative Input for Remote Diode. DXN is normally biased to a diodevoltage above ground.
Combined Current Source and ADC Positive Input for Remote Diode. Place a 2200pF capacitor between
DXP and DXN for noise filtering.
Supply Voltage Input. Bypass with a 0.1µF to GND.
SPI Clock Input

Analog Devices │ 5

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Detailed Description

taking CS low, any conversion in progress is stopped,
and the rising-edge of CS always starts a fresh
conversion and resets the interface. This permits
triggering a con-version at any time so that the power
consumption of the MAX6627 can be overcome, if
needed. Both devices operate with input voltages between+3.0V and +5.5V and are specified between -55°C and+125°C. The MAX6627/MAX6628 come in space-saving
8-pin SOT23 and TDFN packages.

Remote accuracy is ±1°C when the temperature of
the remote diode is between 0°C and +125°C and thetemperature of the MAX6627/MAX6628 is +30°C. Data
is available as a 12-bit + sign word with 0.0625°C
resolution. The operating range of the device extends
from -55°C to +125°C, although the architecture of thedevice is capable of interpreting data up to +145°C. The
device itself should never exceed +125°C.

ADC Conversion Sequence

The MAX6627/MAX6628 remote digital thermometers
report the temperature of a remote sensor. The remotesensor is a diode-connected transistor—typically, a
low-cost, easily mounted 2N3904 NPN type—that
replaces conventional thermistors or thermocouples.
These devices can also measure the die temperature ofother ICs, such as µPs or µCs, that contain an on-chip,
diode-connected transistor.

The devices are designed to work in conjunction withan external µC or other intelligent device serving as
the master in thermostatic, process-control, ormonitoring applications. The µC is typically a power
management or keyboard controller, generating SPI serialcommands by “bit-banging” GPIO pins.
Two conversion rates are available; the MAX6627
continuously converts data every 0.5s, and the MAX6628
continuously converts data every 8s. Either device canbe read at any time and provide the data from the lastconversion. The slower version provides minimal power
consumption under all operating conditions. Or, byIdle Mode

Pull CS low to enter idle mode. In idle mode, the ADC
is not converting. The serial interface is still active andtemperature data from the last completed conversion canstill be read.

Power-On Reset

The POR supply voltage of the MAX6627/MAX6628 is
typically 1.6V. Below this supply voltage, the interface
is inactive and the data register is set to the POR state,

8s
SAMPLE
RATE

0.5s
SAMPLE
RATE

0.25s
CONVERSIONTIME
MAX6627

The device powers up as a free-running data converter(Figure 1). The CS pin can be used for conversion
control. The rising-edge of CS resets the interface andstarts a conversion. The falling-edge of CS stops any
conversion in progress, overriding the latency of the part.
Temperature data from the previous completed conversion
is available for read (Table 1 and Table 2). It is required
to maintain CS high for a minimum of 320ms to complete
a conversion.

ADC CONVERTING
ADC IDLE

MAX6628

Figure 1. Free-Running Conversion Time and Rate Relationships

Table 1. Data Output Format
D15

D14

Sign

MSB
Data

www.analog.com

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

LSB
Data

Low

High-Z

High-Z

Analog Devices │ 6

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

tCSS
CS

SCK

tDV

tDO

tTR

SDO
D15

D3

D2

D1

D0

Figure 2. SPI Timing Diagram

Table 2. Temperature Data Format(Two’s Complement)
TEMPERATURE(°C)

in Table 3. The MAX6627/MAX6628 can also directly
measure the die temperature of CPUs and other ICs with
on-board temperature-sensing diodes.

DIGITAL OUTPUT (BINARY)
D15–D3

D2

D1, D0150

0,1001,0110,0000

0

XX

125

0,0111,1101,0000

0

XX

25

0,0001,1001,0000

0XX

0.06250,0000,0000,0001

0

XX

0

0,0000,0000,0000

0XX-0.0625

1,1111,1111,1111

0

XX

-25

1,1110,0111,0000

0

XX

-55

1,1100,1001,0000

0XX

0°C. When power is first applied and VCC rises above
1.6V (typ), the device starts to convert, although temperature
reading is not recommended at VCC levels below 3.0V.

Serial Interface

Figure 2 is the serial interface timing diagram. The datais latched into the shift register on the falling-edge of
the CS signal and then clocked out at the SDO pin on
the falling-edge of SCK with the most-significant bit(MSB) first. There are 16 edges of data per frame. The
last 2 bits, D0 and D1, are always in high-impedance
mode. The falling-edge of CS stops any conversion inprogress, and the rising-edge of CS always starts a newconversion and resets the interface. It is required to maintaina 320ms minimum pulse width of high CS signal before aconversion starts.

Applications Information
Remote-Diode Selection

Temperature accuracy depends upon having a goodquality, diode-connected, small-signal transistor. Accuracy
has been experimentally verified for all of the devices listed

www.analog.com

The transistor must be a small-signal type with arela-tively high forward voltage. This ensures that the
input voltage is within the A/D input voltage range. The
forward voltage must be greater than 0.25V at 10µA at
the highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expected
temperature. The base resistance has to be less than100Ω. Tight specification of forward-current gain (+50
to +150, for example) indicates that the manufacturer
has good process control and that the devices haveconsistent characteristics.

ADC Noise Filtering

The integrating ADC has inherently good noise
rejection, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
places constraints on high-frequency noise rejection. Layout the PCB carefully with proper external noise filteringfor high-accuracy remote measurements in electricallynoisy environments.

Table 3. SOT23-Type Remote-Sensor
Transistor Manufacturers
MANUFACTURER

MODEL

Central Semiconductor (USA)

CMPT3904

Motorola (USA)

MMBT3904

Rohm Semiconductor (Japan)

SST3904

Siemens (Germany)
Zetex (England)

SMBT3904
FMMT3904CT-ND

Note: Transistors must be diode connected (Short the Base to
the Collector).

Analog Devices │ 7

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Filter high-frequency electromagnetic interference (EMI)at DXP and DXN with an external 2200pF capacitor
connected between the two inputs. This capacitor canbe increased to about 3300pF (max), including cablecapacitance. A capacitance higher than 3300pF
introduces errors due to the rise time of the switchedcurrent source.

8) Placing an electrically clean copper ground plane
between the DXP/DXN traces and traces carrying
high-frequency noise signals helps reduce EMI.

PCB Layout

Twisted Pair and Shielded Cables

1) Place the MAX6627/MAX6628 as close as practicalto the remote diode. In a noisy environment, such as
a computer motherboard, this distance can be 4in to
8in, or more, as long as the worst noise sources (suchas CRTs, clock generators, memory buses, and ISA/
PCI buses) are avoided.
2) Do not route the DXP/DXN lines next to the deflection
coils of a CRT. Also, do not route the traces across afast memory bus, which can easily introduce +30°C
error, even with good filtering. Otherwise, most noise
sources are fairly benign.
3) Route the DXP and DXN traces parallel and close
to each other, away from any high-voltage traces
such as +12VDC. Avoid leakage currents from PCB
contamination. A 20MΩ leakage path from DXP toground causes approximately +1°C error.
4) Connect guard traces to GND on either side of the
DXP/DXN traces (Figure 3). With guard traces in place,routing near high-voltage traces is no longer an issue.
5) Route as few vias and crossunders as possible tominimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure thatboth the DXP and the DXN paths have matching
thermocouples. In general, PCB-induced
thermocouples are not a serious problem. A copper
solder thermocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP/DXN tocause a +1°C measurement error, so most parasitic
thermocouple errors are swamped out.

widths and spacings recommended in Figure 3 are
not absolutely necessary (as they offer only a minor
improvement in leakage and noise), but use themwhere practical.

For remote-sensor distances longer than 8in, or in particularly
noisy environments, a twisted pair is recommended. Its
practical length is 6ft to 12ft (typ) before noise becomesa problem, as tested in a noisy electronics laboratory. For
longer distances, the best solution is a shielded twisted
pair like that used for audio microphones. For example,
Belden #8451 works well for distances up to 100ft in anoisy environment. Connect the twisted pair to DXP and
DXN and the shield to ground, and leave the shield’s
remote end unterminated. Excess capacitance at DXN or
DXP limits practical remote-sensor distances (see Typical
Operating Characteristics).
For very long cable runs, the cable’s parasitic capacitanceoften provides noise filtering, so the recommended 2200pF
capacitor can often be removed or reduced in value. Cable
resistance also affects remote-sensor accuracy. A 1Ω series
resistance introduces about +1/2°C error.

GND
10mils
10milsDXPMINIMUM

10mils

DXN
10mils
GND

Figure 3. Recommended DXP/DXN PC Traces

7) Use wide traces. Narrow traces are more inductive and tend to pick up radiated noise. The 10mil

www.analog.com

Analog Devices │ 8

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Functional Diagram
VCC

SDO

DXP
12-BIT + SIGN
ADC

DXN

PIN-PACKAGE
8 SOT23
8 SOT23
8 TDFN-EP*
8 SOT23
8 TDFN-EP*

SCK
CS

Package Information

Ordering Information
PART
MAX6627MKA#TG16
MAX6627MKA+T
MAX6627MTA+T
MAX6628MKA+T
MAX6628MTA+TSPIINTERFACE

TOP MARK
AEQD
AAEQ
AUT
AAER
AUU

Note: All devices are specified over the -55°C to +125°C operating
temperature range.
#Denotes a RoHS-compliant device that may include lead(Pb)that is exempt under the RoHS requirements.
+Denotes a lead-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.

For the latest package outline information and land patterns(footprints), go to www.maximintegrated.com/packages. Notethat a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGETYPE

PACKAGECODEOUTLINENO.

LAND
PATTERN NO.

8 SOT23

K8F+4

21-007890-0176

8 TDFN-EP

T833+221-0137

90-0059

Chip Information
PROCESS: BiCMOS

www.analog.com

Analog Devices │ 9

MAX6627/MAX6628

Remote ±1°C Accurate Digital Temperature
Sensors with SPI-Compatible Serial Interface

Revision History
REVISION REVISIONNUMBERDATE

PAGESCHANGEDDESCRIPTION

0

4/01

Initial release

—

1

7/01

Removed future status from the MAX6628; changed ICONV from 600µA (max) to650µA (max) in the Electrical Characteristics table; replaced TOC1 in the Typical
Operating Characteristics section

1, 2, 42

4/04

Updated the lead temperature information in the Absolute Maximum Ratings section;
updated the notes for the Electrical Characteristics table

2, 3

3

4/06

Added the TDFN package; updated Table 3; removed transistor count from the Chip
Information section

1, 2, 5, 6, 7,
8, 10

4

8/08

Added missing exposed pad description, updated ordering part numbers, and updated
pin name for pin 7

1–4, 6, 8–11

5

6/11

Corrected the top mark information and SOT23 part number in the Ordering Informationtable; added the soldering information to the Absolute Maximum Ratings section; added
the land pattern numbers to the Package Information table

1, 2, 86

4/14

Updated Applications

1

7

3/16

Adding MAX6628MKA+ to Ordering Information table

8

8

6/18

Updated Ordering Information table

9

9

1/21

Updated Package Information table

9

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 other rights of third parties that
may result from its use.Specifications subject to change without notice. No license is granted by implicationor
otherwise under any patent or patent rights of Analog Devices. Trademarks andregistered trademarks are theproperty of their respective owners.

w w w . a n a l o g . c o mAnalog Devices │ 10