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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, typically
a low-cost, easily mounted 2N3904 NPN type that
replaces conventional thermistors or thermocouples. The
devices can also measure the die temperature of other
ICs, 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 the
devices is +30°C. The temperature is converted to a 12-bit +
sign word with 0.0625°C resolution. The architecture of the
device is capable of interpreting data as high as +145°C from
the 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 and
provide 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 and
lead-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 these
or 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 affect
device 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.)
PARAMETER
SYMBOL
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
Time Between Conversion
Starts
Conversion Time
0.7
0.0625
tSAMPLE
MAX6627
0.5
MAX6628
8
250
°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
MAX6628
30
50
VCC, falling edge
1.6
POWER SUPPLY
Average Operating Current
Power-On Reset (POR)
Threshold
Current Sourcing for Diode
www.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.)
PARAMETER
SYMBOL
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
0.7 x
VCC
VCS = VSCK = GND or VCC
V
1
µA
LOGIC OUTPUTS (SDO)
Output Low Voltage
VOL
ISINK = 1.6mA
Output High Voltage
VOH
ISOURCE = 1.6mA
0.4
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
80
ns
CS Fall to SCK Rise
tCSS
CLOAD = 10pF
CS Fall to Output Enable
tDV
CLOAD = 10pF
80
ns
CS Rise to Output Disable
tTR
CLOAD = 10pF
50
ns
SCK Fall to Output Data Valid
tDO
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
MAX6628
50
TA = +25°C
1
MAX6627/8 toc02
TA = +70°C
0
TA = 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 FREQUENCY
RESPONSE TO THERMAL SHOCK
TEMPERATURE ERROR
vs. DXP/DXN CAPACITANCE
8
6
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 WAVE
APPLIED TO VCC WITH NO
0.1µF CAPACITOR
10
0
-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
10,000
15,000
20,000
CAPACITANCE (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
1
2
GND DXN
3
4
DXP
VCC
TDFN
Pin Description
PIN
NAME
1
GND
2
DXN
3
DXP
4
5
VCC
SCK
6
CS
7
SDO
SPI Data Output
8
N.C.
No Connect. Internally not connected. Can be connected to GND for improved thermal conductivity.
—
EP
www.analog.com
FUNCTION
Ground
Combined Current Sink and ADC Negative Input for Remote Diode. DXN is normally biased to a diode
voltage 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
Chip-Select Input. Pulling CS low initiates an idle state, but the SPI interface is still enabled. A rising-edge
of CS initiates the next conversion.
Exposed Pad. Internally connected to GND. Connect to a large ground plane to maximize thermal
performance. Not intended as an electrical connection point.
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 the
temperature 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 the
device 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 remote
sensor 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 of
other ICs, such as µPs or µCs, that contain an on-chip,
diode-connected transistor.
The devices are designed to work in conjunction with
an external µC or other intelligent device serving as
the master in thermostatic, process-control, or
monitoring applications. The µC is typically a power
management or keyboard controller, generating SPI serial
commands 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 can
be read at any time and provide the data from the last
conversion. The slower version provides minimal power
consumption under all operating conditions. Or, by
Idle Mode
Pull CS low to enter idle mode. In idle mode, the ADC
is not converting. The serial interface is still active and
temperature data from the last completed conversion can
still 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
CONVERSION
TIME
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 and
starts 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, D0
150
0,1001,0110,0000
0
XX
125
0,0111,1101,0000
0
XX
25
0,0001,1001,0000
0
XX
0.0625
0,0000,0000,0001
0
XX
0
0,0000,0000,0000
0
XX
-0.0625
1,1111,1111,1111
0
XX
-25
1,1110,0111,0000
0
XX
-55
1,1100,1001,0000
0
XX
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 data
is 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 in
progress, and the rising-edge of CS always starts a new
conversion and resets the interface. It is required to maintain
a 320ms minimum pulse width of high CS signal before a
conversion 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 a
rela-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 than
100Ω. Tight specification of forward-current gain (+50
to +150, for example) indicates that the manufacturer
has good process control and that the devices have
consistent 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. Lay
out the PCB carefully with proper external noise filtering
for high-accuracy remote measurements in electrically
noisy environments.
Table 3. SOT23-Type Remote-Sensor
Transistor Manufacturers
MANUFACTURER
MODEL
Central Semiconductor (USA)
CMPT3904
Motorola (USA)
MMBT3904
Rohm Semiconductor (Japan)
Siemens (Germany)
Zetex (England)
SST3904
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 can
be increased to about 3300pF (max), including cable
capacitance. 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 practical
to 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 (such
as 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 a
fast 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 to
ground 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 to
minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both 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 to
cause 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 them
where 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 becomes
a 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 a
noisy 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 capacitance
often 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
10mils
DXP
MINIMUM
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+T
SPI
INTERFACE
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. Note
that 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.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
8 SOT23
K8F+4
21-0078
90-0176
8 TDFN-EP
T833+2
21-0137
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 REVISION
NUMBER
DATE
PAGES
CHANGED
DESCRIPTION
0
4/01
Initial release
—
1
7/01
Removed future status from the MAX6628; changed ICONV from 600µA (max) to
650µA (max) in the Electrical Characteristics table; replaced TOC1 in the Typical
Operating Characteristics section
2
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 Information
table; added the soldering information to the Absolute Maximum Ratings section; added
the land pattern numbers to the Package Information table
6
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
1, 2, 4
1, 2, 8
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 the
property of their respective owners.
w w w . a n a l o g . c o m
Analog Devices │ 10