MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
General Description
The MAX1617 is a precise digital thermometer that
reports the temperature of both a remote sensor and its
own package. The remote sensor is a diode-connected
transistor—typically a low-cost, easily mounted 2N3904
NPN type—that replaces conventional thermistors or
thermocouples. Remote accuracy is ±3°C for multiple
transistor manufacturers, with no calibration needed. The
remote channel can also measure the die temperature of
other ICs, such as microprocessors, that contain an onchip, diode-connected transistor.
The 2-wire serial interface accepts standard System
Management Bus (SMBus) Write Byte, Read Byte, Send
Byte, and Receive Byte commands to program the alarm
thresholds and to read temperature data. The data format
is 7 bits plus sign, with each bit corresponding to 1°C, in
twos-complement format. Measurements can be done
automatically and autonomously, with the conversion rate
programmed by the user or programmed to operate in a
single-shot mode. The adjustable rate allows the user to
control the supply-current drain.
The MAX1617 is available in a small, 16-pin QSOP
surface-mount package.
Applications
●● Desktop and Notebook
Computers
●● Smart Battery Packs
●● LAN Servers
●● Industrial Controls
●●
●●
●●
Central Office
Telecom Equipment
Test and Measurement
Multi-Chip Modules
Pin Configuration
TOP VIEW
N.C. 1
●● SMBus 2-Wire Serial Interface
●● Programmable Under/Overtemperature Alarms
●● Supports SMBus Alert Response
●● Accuracy:
• ±2°C (+60°C to +100°C, local)
• ±3°C (-40°C to +125°C, local)
• ±3°C (+60°C to +100°C, remote)
●● 3μA (typ) Standby Supply Current
●● 70μA (max) Supply Current in Auto-Convert Mode
●● +3V to +5.5V Supply Range
●● Small, 16-Pin QSOP Package
Ordering Information
PART
TEMP. RANGE
PIN-PACKAGE
MAX1617MEE+
-55°C to +125°C
16 QSOP
+Denotes a lead-free package.
3V TO 5.5V
0.1µF
+
16 N.C.
VCC 2
15 STBY
14 SMBCLK
MAX1617
VCC
13 N.C.
ADD1 6
11 ALERT
GND 7
10 ADD0
GND 8
9
QSOP
N.C.
STBY
10k EACH
MAX1617
DXP
12 SMBDATA
N.C. 5
19-1265; Rev 3; 11/16
●● No Calibration Required
Typical Operating Circuit
DXP 3
DXN 4
Features
●● Two Channels: Measures Both Remote and Local
Temperatures
SMBCLK
SMBDATA
2N3904
2200pF
DXN
ALERT
ADD0 ADD1 GND
CLOCK
DATA
INTERRUPT
TO µC
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Absolute Maximum Ratings
VCC to GND.............................................................-0.3V to +6V
DXP, ADD_ to GND................................... -0.3V to (VCC + 0.3V)
DXN to GND..........................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, STBY to GND.........-0.3V to +6V
SMBDATA, ALERT Current................................. -1mA to +50mA
DXN Current........................................................................±1mA
ESD Protection (SMBCLK, SMBDATA,
ALERT, human body model)..........................................4000V
ESD Protection (other pins, human body model)..............2000V
Continuous Power Dissipation (TA = +70°C)
QSOP (derate 8.30mW/°C above +70°C)....................667mW
Operating Temperature Range.......................... -55°C to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65°C to +165°C
Lead Temperature (soldering, 10sec).............................. +300°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
(VCC = +3.3V, TA = 0°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ADC AND POWER SUPPLY
Temperature Resolution (Note 2)
Monotonicity guaranteed
8
Initial Temperature Error,
Local Diode (Note 3)
TA = +60°C to +100°C
-2
2
TA = 0°C to +85°C
-3
3
Temperature Error, Remote Diode
(Notes 3 and 4)
TR = +60°C to +100°C
-3
3
TR = -55°C to +125°C
-5
5
TA = +60°C to +100°C
-2.5
2.5
TA = 0°C to +85°C
-3.5
3.5
3.0
5.5
V
2.95
V
Temperature Error, Local Diode
(Notes 2 and 3)
Including long-term drift
Supply-Voltage Range
Undervoltage Lockout Threshold
VCC input, disables A/D conversion, rising edge
2.60
2.80
VCC, falling edge
1.0
1.7
Undervoltage Lockout Hysteresis
Power-On Reset Threshold
50
POR Threshold Hysteresis
Logic inputs
forced to VCC
or GND
Average Operating Supply Current
Auto-convert mode, average
measured over 4sec. Logic
inputs forced to VCC or GND.
Conversion Time
From stop bit to conversion complete (both channels)
94
Conversion Rate Timing Error
Auto-convert mode
-25
SMBus static
3
Hardware or software standby,
SMBCLK at 10kHz
4
DXP forced to 1.5V
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°C
°C
V
mV
10
µA
0.25 conv/sec
35
70
2.0 conv/sec
120
180
125
156
ms
25
%
High level
80
100
120
Low level
8
10
12
DXN Source Voltage
Address Pin Bias Current
°C
mV
2.5
50
Standby Supply Current
Remote-Diode Source Current
Bits
ADD0, ADD1; momentary upon power-on reset
µA
µA
0.7
V
160
µA
Maxim Integrated │ 2
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Electrical Characteristics (continued)
(VCC = +3.3V, TA = 0°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus INTERFACE
Logic Input High Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Input Low Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Output Low Sink Current
ALERT, SMBDATA forced to 0.4V
ALERT Output High Leakage
Current
ALERT forced to 5.5V
Logic Input Current
Logic inputs forced to VCC or GND
2.2
V
0.8
6
V
mA
-1
1
µA
1
µA
100
kHz
SMBus Input Capacitance
SMBCLK, SMBDATA
SMBus Clock Frequency
(Note 5)
DC
5
SMBCLK Clock Low Time
tLOW, 10% to 10% points
4.7
µs
SMBCLK Clock High Time
tHIGH, 90% to 90% points
4
µs
4.7
µs
500
ns
SMBus Start-Condition Setup Time
pF
SMBus Repeated Start-Condition
Setup Time
tSU:STA, 90% to 90% points
SMBus Start-Condition Hold Time
tHD:STA, 10% of SMBDATA to 90% of SMBCLK
4
µs
SMBus Stop-Condition Setup Time tSU:STO, 90% of SMBCLK to 10% of SMBDATA
4
µs
800
ns
0
µs
SMBus Data Valid to SMBCLK
Rising-Edge Time
tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK
SMBus Data-Hold Time
tHD:DAT (Note 6)
SMBCLK Falling Edge to SMBus
Data-Valid Time
Master clocking in data
1
µs
MAX
UNITS
Electrical Characteristics
(VCC = +3.3V, TA = 5.5°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
ADC AND POWER SUPPLY
Temperature Resolution (Note 1)
Monotonicity guaranteed
8
Initial Temperature Error,
Local Diode (Note 3)
TA = +60°C to +100°C
-2
2
TA = 0°C to +85°C
-3
3
TR = +60°C to +100°C
-3
3
TR = -55°C to +125°C
-5
5
3.0
5.5
V
156
ms
25
%
Temperature Error, Remote Diode
(Notes 3 and 4)
Supply-Voltage Range
Conversion Time
From stop bit to conversion complete (both channels)
94
Conversion Rate Timing Error
Auto-convert mode
-25
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Bits
125
°C
°C
Maxim Integrated │ 3
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Electrical Characteristics (continued)
(VCC = +3.3V, TA = 5.5°C to +125°C, unless otherwise noted.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus INTERFACE
VCC = 3V
2.2
VCC = 5.5V
2.4
Logic Input High Voltage
STBY, SMBCLK, SMBDATA
Logic Input Low Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Output Low Sink Current
ALERT, SMBDATA forced to 0.4V
ALERT Output High Leakage
Current
ALERT forced to 5.5V
Logic Input Current
Logic inputs forced to VCC or GND
V
0.8
V
6
mA
-2
1
µA
2
µA
Note 1: All devices 100% production tested at TA = +85°C. Limits over temperature are guaranteed by design.
Note 2: Guaranteed but not 100% tested.
Note 3: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1617 device temperature is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization error plus the +1/2°C offset
used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to +100°C temperature range. See
Table 2.
Note 4: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. See
Remote Diode Selection for remote diode forward voltage requirements.
Note 5: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it
violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus.
Note 6: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of
SMBCLK’s falling edge.
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
PATH = DXP TO GND
0
-10
1
3
10
30
LEAKAGE RESISTANCE (MΩ)
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ZETEX FMMT3904
0
MOTOROLA MMBT3904
SAMSUNG KST3904
-1
12
VIN = SQUARE WAVE APPLIED TO
VCC WITH NO 0.1µF VCC CAPACITOR
9
VIN = 250mVp-p
REMOTE DIODE
6
VIN = 250mVp-p
LOCAL DIODE
VIN = 100mVp-p
REMOTE DIODE
3
RANDOM
SAMPLES
PATH = DXP TO VCC (5V)
-20
MAX1617TOC02
1
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCY
TEMPERATURE ERROR (°C)
10
2
TEMPERATURE ERROR (°C)
MAX1617TOC01
TEMPERATURE ERROR (°C)
20
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
100
-2
-50
0
50
100
TEMPERATURE (°C)
150
0
MAX1617TOC03
TEMPERATURE ERROR
vs. PCB RESISTANCE
50
500
5k
50k
500k
5M
50M
FREQUENCY (Hz)
Maxim Integrated │ 4
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
20
VIN = 50mVp-p
10
VIN = 25mVp-p
500
5k
50k
500k
5M
-5
50M
MAX1617TOC05
MAX1617TOC06
0
50
500
5k
50k
500k
5M
-5
50M
50
500
5k
50k
500k
5M
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TEMPERATURE ERROR vs.
DXP–DXN CAPACITANCE
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
10
35
SMBCLK IS
DRIVEN RAIL-TO-RAIL
30
25
VCC = 5V
20
15
10
VCC = 3.3V
5
20
40
60
80
0
100
1k
DXP-DXN CAPACITANCE (nF)
10k
100k
0
1
CONVERSION RATE (Hz)
4
4
5
75
50
0
2
3
100
25
100
1
2
SUPPLY VOLTAGE (V)
RESPONSE TO THERMAL SHOCK
200
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6
125
TEMPERATURE (°C)
VCC = 5V
AVERAGED MEASUREMENTS
0 0.0625 0.125 0.25 0.5
ADD0,
ADD1
= HIGH-Z
SMBCLK FREQUENCY (Hz)
300
0
20
0
1000k
MAX1617TOC10
SUPPLY CURRENT (µA)
400
60
3
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
500
ADD0,
ADD1
= GND
MAX1617TOC11
0
100
50M
MAX1617TOC09
MAX1617TOC07
VCC = 5V
0
5
VIN = 3mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
20
TEMPERATURE ERROR (°C)
0
MAX1617TOC08
50
VIN = 10mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
SUPPLY CURRENT (µA)
0
10
TEMPERATURE ERROR (°C)
VIN = 100mVp-p
5
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
AC COUPLED TO DXN
SUPPLY CURRENT (µA)
TEMPERATURE ERROR (°C)
30
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
MAX1617TOC04
TEMPERATURE ERROR vs.
COMMON-MODE NOISE FREQUENCY
8
16-QSOP IMMERSED
IN +115°C FLUORINERT BATH
T = -2
T=0
T=2
T=4
T=6
T=8
T = 10
TIME (sec)
Maxim Integrated │ 5
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Pin Description
PIN
NAME
FUNCTION
1, 5, 9,
13, 16
N.C.
No Connection. Not internally connected. May be used for PCB trace routing.
2
VCC
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1μF capacitor. A 200Ω series resistor is
recommended but not required for additional noise filtering.
3
DXP
Combined Current Source and A/D Positive Input for remote-diode channel. Do not leave DXP
unconnected; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and
DXN for noise filtering.
4
DXN
Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above
ground.
6
ADD1
SMBus Address Select pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance
(>50pF) at the address pins when unconnected may cause address-recognition problems.
7, 8
GND
Ground
10
ADD0
SMBus Slave Address Select pin
11
ALERT
SMBus Alert (interrupt) Output, open drain
12
SMBDATA
SMBus Serial-Data Input/Output, open drain
14
SMBCLK
SMBus Serial-Clock Input
15
STBY
Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
Detailed Description
The MAX1617 is a temperature sensor designed to work
in conjunction with an external microcontroller (μC) or
other intelligence in thermostatic, process-control, or
monitoring applications. The μC is typically a power-management or keyboard controller, generating SMBus serial
commands by “bit-banging” general-purpose input-output
(GPIO) pins or via a dedicated SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1617
contains a switched current source, a multiplexer, an
ADC, an SMBus interface, and associated control logic
(Figure 1). Temperature data from the ADC is loaded into
two data registers, where it is automatically compared
with data previously stored in four over/under-temperature alarm registers.
ADC and Multiplexer
The ADC is an averaging type that integrates over a
60ms period (each channel, typical), with excellent
noise rejection.
The multiplexer automatically steers bias currents through
the remote and local diodes, measures their forward voltages, and computes their temperatures. Both channels
are automatically converted once the conversion process
has started, either in free-running or single-shot mode.
If one of the two channels is not used, the device still
performs both measurements, and the user can simply
ignore the results of the unused channel. If the remote
diode channel is unused, tie DXP to DXN rather than leaving the pins open.
The DXN input is biased at 0.65V typical above ground
by an internal diode to set up the analog-to-digital (A/D)
inputs for a differential measurement. The typical DXP–
DXN differential input voltage range is 0.25V to 0.95V.
To ensure proper operation over full temperature range,
ensure VDXP ≤ (0.78 x VCC - 1.1) volts.
Excess resistance in series with the remote diode causes
about +1/2°C error per ohm. Likewise, 200μV of offset
voltage forced on DXP–DXN causes about 1°C error.
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Maxim Integrated │ 6
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ALERT
GND
DXN
DXP
VCC
Q
R
S
DIGITAL COMPARATOR
(REMOTE)
SELECTED VIA
SLAVE ADD = 0001 100
DIGITAL COMPARATOR
(LOCAL)
8
LOW-TEMPERATURE
THRESHOLD (LOCAL TLOW)
LOW-TEMPERATURE
THRESHOLD (REMOTE TLOW)
8
8
HIGH-TEMPERATURE
THRESHOLD (LOCAL THIGH)
HIGH-TEMPERATURE
THRESHOLD (REMOTE THIGH)
8
CONTROL
LOGIC
8
ADC
LOCAL TEMPERATURE
DATA REGISTER
-
+
REMOTE TEMPERATURE
DATA REGISTER
DIODE
FAULT
LOCAL
REMOTE
8
-
+
-
+
MUX
MAX1617
2
8
READ
ALERT RESPONSE
ADDRESS REGISTER
CONVERSION RATE
REGISTER
CONFIGURATION
BYTE REGISTER
STATUS BYTE REGISTER
8
WRITE
SMBUS
7
ADD1
ADDRESS
DECODER
ADD0
COMMAND BYTE
(INDEX) REGISTER
STBY
SMBCLK
SMBDATA
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Figure 1. Functional Diagram
Maxim Integrated │ 7
MAX1617
A/D Conversion Sequence
If a Start command is written (or generated automatically
in the free-running auto-convert mode), both channels
are converted, and the results of both measurements are
available after the end of conversion. A BUSY status bit in
the status byte shows that the device is actually performing
a new conversion; however, even if the ADC is busy, the
results of the previous conversion are always available.
Remote-Diode Selection
Temperature accuracy depends on having a good-quality,
diode-connected small-signal transistor. See Table 1 for a
recommended list of diode-connected small-signal transistors. The MAX1617 can also directly measure the die
temperature of CPUs and other integrated circuits having
on-board temperature-sensing diodes.
Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 1. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
MODEL NUMBER
Central Semiconductor (USA)
CMPT3904
Motorola (USA)
MMBT3904
National Semiconductor (USA)
MMBT3904
Rohm Semiconductor (Japan)
SST3904
Samsung (Korea)
KST3904-TF
Siemens (Germany)
SMBT3904
Zetex (England)
FMMT3904CT-ND
Note: Transistors must be diode-connected (base shorted to
collector).
The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input voltage range can be violated. The forward voltage must be
greater than 0.25V at 10μA; check to ensure this is true
at the highest expected temperature. The forward voltage (VDXP - VDXN) must be less than 0.95V at 100μA;
additionally, ensure the maximum VDXP (DXP voltage)
≤ (0.78 x VCC - 1.1) volts over your expected range of
temperature. Large power transistors don’t work at all.
Also, ensure that the base resistance is less than 100Ω.
Tight specifications for forward-current gain (+50 to +150,
for example) indicate that the manufacturer has good process controls and that the devices have consistent VBE
characteristics.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
worst-case error occurs when auto-converting at the fastest rate and simultaneously sinking maximum current at
the ALERT output. For example, at an 8Hz rate and with
ALERT sinking 1mA, the typical power dissipation is VCC
x 450μA plus 0.4V x 1mA. Package theta J-A is about
150°C/W, so with VCC = 5V and no copper PCB heatsinking, the resulting temperature rise is:
For heat-sink mounting, the 500-32BT02-000 thermal
sensor from Fenwal Electronics is a good choice. This
device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (Fenwal
Inc., Milford, MA, 508-478-6000).
ADC Noise Filtering
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the MAX1617’s
effective accuracy. The thermal time constant of the
QSOP-16 package is about 140sec in still air. For the
MAX1617 junction temperature to settle to within +1°C
after a sudden +100°C change requires about five time
constants or 12 minutes. The use of smaller packages
for remote sensors, such as SOT23s, improves the situation. Take care to account for thermal gradients between
the heat source and the sensor, and ensure that stray air
currents across the sensor package do not interfere with
measurement accuracy.
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dT = 2.7mW x 150°C/W = 0.4°C
Even with these contrived circumstances, it is difficult to
introduce significant self-heating errors.
The ADC is an integrating type with 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;
therefore, careful PCB layout and proper external noise
filtering are required for high-accuracy remote measurements in electrically noisy environments.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. This value can be
increased to about 3300pF (max), including cable capacitance. Higher capacitance than 3300pF introduces errors
due to the rise time of the switched current source.
Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature, typically
by +1°C to +10°C, depending on the frequency and amplitude (see Typical Operating Characteristics).
Maxim Integrated │ 8
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
PCB Layout
1) Place the MAX1617 as close as practical to the remote
diode. In a noisy environment, such as a computer
motherboard, this distance can be 4 in. to 8 in. (typical)
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 in parallel and in close
proximity to each other, away from any high-voltage
traces such as +12VDC. Leakage currents from PCB
contamination must be dealt with carefully, since a
20MΩ leakage path from DXP to ground causes about
+1°C error.
4) Connect guard traces to GND on either side of the
DXP–DXN traces (Figure 2). With guard traces in place,
routing near high-voltage traces is no longer an issue.
5) Route through 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 about 200μV of
voltage error at DXP–DXN to cause a +1°C measurement error. So, most parasitic thermocouple errors are
swamped out.
7) Use wide traces. Narrow ones are more inductive and
tend to pick up radiated noise. The 10 mil widths and
spacings recommended in Figure 2 aren’t absolutely
necessary (as they offer only a minor improvement in
leakage and noise), but try to use them where practical.
8) Keep in mind that copper can’t be used as an EMI
shield, and only ferrous materials such as steel work
well. Placing a copper ground plane between the DXPDXN traces and traces carrying high-frequency noise
signals does not help reduce EMI.
PCB Layout Checklist
● Place the MAX1617 close to a remote diode.
● Keep traces away from high voltages (+12V bus).
● Keep traces away from fast data buses and CRTs.
● Use recommended trace widths and spacings.
● Place a ground plane under the traces.
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GND
10MILS
10MILS
DXP
MINIMUM
10MILS
DXN
10MILS
GND
Figure 2. Recommended DXP/DXN PC Traces
● Use guard traces flanking DXP and DXN and connecting to GND.
● Place the noise filter and the 0.1μF VCC bypass
capacitors close to the MAX1617.
● Add a 200Ω resistor in series with VCC for best noise
filtering (see Typical Operating Circuit).
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 in., or in particularly noisy environments, a twisted pair is recommended.
Its practical length is 6 feet to 12 feet (typical) 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
100 feet in a noisy environment. Connect the twisted pair
to DXP and DXN and the shield to GND, and leave the
shield’s remote end unterminated.
Excess capacitance at DX_ 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 2200pF capacitor can
often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy; 1Ω
series resistance introduces about +1/2°C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply- current drain to less than 10μA. Enter standby mode
by forcing the STBY pin low or via the RUN/STOP bit in
the configuration byte register. Hardware and software
standby modes behave almost identically: all data is
retained in memory, and the SMB interface is alive and
listening for reads and writes. The only difference is that
in hardware standby mode, the one-shot command does
not initiate a conversion.
Standby mode is not a shutdown mode. With activity on
the SMBus, extra supply current is drawn (see Typical
Operating Characteristics). In software standby mode,
Maxim Integrated │ 9
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
SMBus Digital Interface
the MAX1617 can be forced to perform A/D conversions
via the one-shot command, despite the RUN/STOP bit
being high.
From a software perspective, the MAX1617 appears as a
set of byte-wide registers that contain temperature data,
alarm threshold values, or control bits. A standard SMBus
2-wire serial interface is used to read temperature data
and write control bits and alarm threshold data. Each A/D
channel within the device responds to the same SMBus
slave address for normal reads and writes.
Activate hardware standby mode by forcing the STBY pin
low. In a notebook computer, this line may be connected
to the system SUSTAT# suspend-state signal.
The STBY pin low state overrides any software conversion
command. If a hardware or software standby command is
received while a conversion is in progress, the conversion
cycle is truncated, and the data from that conversion is not
latched into either temperature reading register. The previous data is not changed and remains available.
The MAX1617 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 3). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data register was previously selected by a Read Byte instruction.
Use caution with the shorter protocols in multi-master
systems, since a second master could overwrite the command byte without informing the first master.
Supply-current drain during the 125ms conversion period
is always about 450μA. Slowing down the conversion
rate reduces the average supply current (see Typical
Operating Characteristics). In between conversions, the
instantaneous supply current is about 25μA due to the
current consumed by the conversion rate timer. In standby mode, supply current drops to about 3μA. At very low
supply voltages (under the power-on-reset threshold), the
supply current is higher due to the address pin bias currents. It can be as high as 100μA, depending on ADD0
and ADD1 settings.
The temperature data format is 7 bits plus sign in twos-complement form for each channel, with each data bit representing 1°C (Table 2), transmitted MSB first. Measurements are
offset by +1/2°C to minimize internal rounding errors; for
example, +99.6°C is reported as +100°C.
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
DATA
8 bits
Slave Address: equivalent to chip-select line of
a 3-wire interface
ACK
P
8 bits
Command Byte: selects which
register you are writing to
1
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Read Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
Slave Address: equivalent to chip-select line
ADDRESS
7 bits
Command Byte: selects
which register you are
reading from
RD
ACK
DATA
///
P
8 bits
Slave Address: repeated
due to change in dataflow direction
Data Byte: reads from
the register set by the
command byte
Receive Byte Format
WR
ACK
COMMAND
ACK
8 bits
Command Byte: sends command with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
ADDRESS
7 bits
Send Byte Format
S
S
8 bits
Shaded = Slave transmission
/// = Not acknowledged
P
S
ADDRESS
7 bits
RD
ACK
DATA
///
P
8 bits
Data Byte: reads data from
the register commanded
by the last Read Byte or
Write Byte transmission;
also used for SMBus Alert
Response return address
Figure 3. SMBus Protocols
www.maximintegrated.com
Maxim Integrated │ 10
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 2. Data Format (Twos-Complement)
DIGITAL OUTPUT
DATA BITS
TEMP.
(°C)
ROUNDED
TEMP.
(°C)
SIGN
MSB
LSB
+130.00
+127
0
111
1111
+127.00
+127
0
111
1111
+126.50
+127
0
111
1111
+126.00
+126
0
111
1110
+25.25
+25
0
001
1001
+0.50
+1
0
000
0001
+0.25
+0
0
000
0000
+0.00
+0
0
000
0000
-0.25
+0
0
000
0000
-0.50
+0
0
000
0000
-0.75
-1
1
111
1111
-1.00
-1
1
111
1111
-25.00
-25
1
110
0111
-25.50
-25
1
110
0110
-54.75
-55
1
100
1001
-55.00
-55
1
100
1001
-65.00
-65
1
011
1111
-70.00
-65
1
011
1111
Alarm Threshold Registers
Four registers store alarm threshold data, with hightemperature (THIGH) and low-temperature (TLOW) registers
for each A/D channel. If either measured temperature
equals or exceeds the corresponding alarm threshold
value, an ALERT interrupt is asserted.
The power-on-reset (POR) state of both THIGH registers
is full scale (0111 1111, or +127°C). The POR state of both
TLOW registers is 1100 1001 or -55°C.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
whether the remote diode has an open-circuit condition.
At the beginning of each conversion, the diode fault is
checked, and the status byte is updated. This fault detector is a simple voltage detector; if DXP rises above VCC
- 1V (typical) due to the diode current source, a fault is
detected. Note that the diode fault isn’t checked until a
conversion is initiated, so immediately after power-on
reset the status byte indicates no fault is present, even if
the diode path is broken.
If the remote channel is shorted (DXP to DXN or DXP
to GND), the ADC reads 0000 0000 so as not to trip
www.maximintegrated.com
Table 3. Read Format for Alert Response
Address (0001100)
BIT
NAME
7
(MSB)
ADD7
6
ADD6
5
ADD5
4
ADD4
3
ADD3
2
ADD2
1
ADD1
0
(LSB)
1
FUNCTION
Provide the current MAX1617
slave address that was latched at
POR (Table 8)
Logic 1
either the THIGH or TLOW alarms at their POR settings.
In applications that are never subjected to 0°C in normal
operation, a 0000 0000 result can be checked to indicate
a fault condition in which DXP is accidentally short circuited. Similarly, if DXP is short circuited to VCC, the ADC
reads +127°C for both remote and local channels, and the
device alarms.
ALERT Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response address.
Interrupts are generated in response to THIGH and TLOW
comparisons and when the remote diode is disconnected
(for continuity fault detection). The interrupt does not halt
automatic conversions; new temperature data continues
to be available over the SMBus interface after ALERT is
asserted. The interrupt output pin is open-drain so that
devices can share a common interrupt line. The interrupt
rate can never exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature (see
Alert Response Address section). Prior to taking corrective action, always check to ensure that an interrupt is
valid by reading the current temperature.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that lack
the complex, expensive logic needed to be a bus master. Upon receiving an ALERT interrupt signal, the host
master can broadcast a Receive Byte transmission to the
Alert Response slave address (0001 100). Then any slave
device that generated an interrupt attempts to identify
itself by putting its own address on the bus (Table 3).
Maxim Integrated │ 11
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 4. Command-Byte Bit Assignments
REGISTER
COMMAND
POR STATE
FUNCTION
RLTS
00h
0000 0000*
Read local temperature: returns latest temperature
RRTE
01h
0000 0000*
Read remote temperature: returns latest temperature
RSL
02h
N/A
RCL
03h
0000 0000
Read configuration byte
Read status byte (flags, busy signal)
RCRA
04h
0000 0010
Read conversion rate byte
RLHN
05h
0111 1111
Read local THIGH limit
RLLI
06h
1100 1001
Read local TLOW limit
RRHI
07h
0111 1111
Read remote THIGH limit
RRLS
08h
1100 1001
Read remote TLOW limit
WCA
09h
N/A
Write configuration byte
WCRW
0Ah
N/A
Write conversion rate byte
WLHO
0Bh
N/A
Write local THIGH limit
WLLM
0Ch
N/A
Write local TLOW limit
WRHA
0Dh
N/A
Write remote THIGH limit
WRLN
0Eh
N/A
Write remote TLOW limit
OSHT
0Fh
N/A
One-shot command (use send-byte format)
*If the device is in hardware standby mode at POR, both temperature registers read 0°C.
The Alert Response can activate several different slave
devices simultaneously, similar to the I2C General Call. If
more than one slave attempts to respond, bus arbitration
rules apply, and the device with the lower address code
wins. The losing device does not generate an acknowledge and continues to hold the ALERT line low until
serviced (implies that the host interrupt input is level-sensitive). Successful reading of the alert response address
clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the various other registers within the
MAX1617. The register’s POR state is 0000 0000, so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current local temperature data.
The one-shot command immediately forces a new conversion cycle to begin. In software standby mode (RUN/
STOP bit = high), a new conversion is begun, after which
the device returns to standby mode. If a conversion is
in progress when a one-shot command is received, the
command is ignored. If a one-shot command is received
in auto-convert mode (RUN/STOP bit = low) between
conversions, a new conversion begins, the conversion
rate timer is reset, and the next automatic conversion
takes place after a full delay elapses.
www.maximintegrated.com
Configuration Byte Functions
The configuration byte register (Table 5) is used to mask
(disable) interrupts and to put the device in software
standby mode. The lower six bits are internally set to
(XX1111), making them “don’t care” bits. Write zeros to
these bits. This register’s contents can be read back over
the serial interface.
Status Byte Functions
The status byte register (Table 6) indicates which (if any)
temperature thresholds have been exceeded. This byte
also indicates whether or not the ADC is converting and
whether there is an open circuit in the remote diode DXP–
DXN path. After POR, the normal state of all the flag bits
is zero, assuming none of the alarm conditions are present. The status byte is cleared by any successful read of
the status byte, unless the fault persists. Note that the
ALERT interrupt latch is not automatically cleared when
the status flag bit is cleared.
When reading the status byte, you must check for internal
bus collisions caused by asynchronous ADC timing, or
else disable the ADC prior to reading the status byte (via
the RUN/STOP bit in the configuration byte). In one-shot
mode, read the status byte only after the conversion is
complete, which is 150ms max after the one-shot conversion is commanded.
Maxim Integrated │ 12
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 5. Configuration-Byte Bit
Assignments
BIT
NAME
POR
STATE
7
(MSB)
MASK
0
Masks all ALERT interrupts
when high.
0
Standby mode control bit.
If high, the device immediately
stops converting
and enters standby mode. If
low, the device converts in
either one-shot or timer mode.
6
5-0
RUN/
STOP
RFU
0
FUNCTION
Reserved for future use
Table 6. Status-Byte Bit Assignments
BIT
NAME
FUNCTION
7
(MSB)
BUSY
A high indicates that the ADC is busy
converting.
6
LHIGH*
A high indicates that the local
hightemperature alarm has activated.
5
LLOW*
A high indicates that the local
lowtemperature alarm has activated.
4
RHIGH*
A high indicates that the remote
hightemperature alarm has activated.
3
RLOW*
A high indicates that the remote
lowtemperature alarm has activated.
2
OPEN*
A high indicates a remote-diode
continuity (open-circuit) fault.
1
RFU
Reserved for future use (returns 0)
0
(LSB)
RFU
Reserved for future use (returns 0)
*These flags stay high until cleared by POR, or until the status
byte register is read.
To check for internal bus collisions, read the status byte. If
the least significant seven bits are ones, discard the data
and read the status byte again. The status bits LHIGH,
LLOW, RHIGH, and RLOW are refreshed on the SMBus
clock edge immediately following the stop condition, so
there is no danger of losing temperature-related status
data as a result of an internal bus collision. The OPEN
status bit (diode continuity fault) is only refreshed at the
beginning of a conversion, so OPEN data is lost. The
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Table 7. Conversion-Rate Control Byte
DATA
CONVERSION
RATE
(Hz)
AVERAGE SUPPLY
CURRENT
(μA typ, at VCC = 3.3V)
00h
0.0625
30
01h
0.125
33
02h
0.25
35
03h
0.5
48
04h
1
70
05h
2
128
06h
4
225
07h
8
425
08h to
FFh
RFU
—
ALERT interrupt latch is independent of the status byte
register, so no false alerts are generated by an internal
bus collision.
When auto-converting, if the THIGH and TLOW limits
are close together, it’s possible for both high-temp and
low-temp status bits to be set, depending on the amount
of time between status read operations (especially when
converting at the fastest rate). In these circumstances, it’s
best not to rely on the status bits to indicate reversals in
long-term temperature changes and instead use a current
temperature reading to establish the trend direction.
Conversion Rate Byte
The conversion rate register (Table 7) programs the time
interval between conversions in free-running auto-convert
mode. This variable rate control reduces the supply current in portable-equipment applications. The conversion
rate byte’s POR state is 02h (0.25Hz). The MAX1617
looks only at the 3 LSB bits of this register, so the upper
5 bits are “don’t care” bits, which should be set to zero.
The conversion rate tolerance is ±25% at any rate setting.
Valid A/D conversion results for both channels are available one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conversion is initiated via the RUN/STOP bit, hardware STBY
pin, one-shot command, or initial power-up. Changing the
conversion rate can also affect the delay until new results
are available. See Table 8.
Maxim Integrated │ 13
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Table 8. RLTS and RRTE Temp Register Update Timing Chart
OPERATING MODE
NEW CONVERSION RATE
(CHANGED VIA WRITE TO
WCRW)
CONVERSION INITIATED BY:
TIME UNTIL RLTS AND RRTE
ARE UPDATED
Auto-Convert
Power-on reset
n/a (0.25Hz)
156ms max
Auto-Convert
1-shot command, while idling
between automatic conversions
n/a
156ms max
Auto-Convert
1-shot command that occurs
during a conversion
n/a
When current conversion is
complete (1-shot is ignored)
Auto-Convert
Rate timer
0.0625Hz
20sec
Auto-Convert
Rate timer
0.125Hz
10sec
Auto-Convert
Rate timer
0.25Hz
5sec
Auto-Convert
Rate timer
0.5Hz
2.5sec
Auto-Convert
Rate timer
1Hz
1.25sec
Auto-Convert
Rate timer
2Hz
625ms
Auto-Convert
Rate timer
4Hz
312.5ms
Auto-Convert
Rate timer
8Hz
237.5ms
Hardware Standby
STBY pin
n/a
156ms
Software Standby
RUN/STOP bit
n/a
156ms
Software Standby
1-shot command
n/a
156ms
Slave Addresses
The MAX1617 appears to the SMBus as one device
having a common address for both ADC channels. The
device address can be set to one of nine different values
by pin-strapping ADD0 and ADD1 so that more than one
MAX1617 can reside on the same bus without address
conflicts (Table 9).
The address pin states are checked at POR only, and the
address data stays latched to reduce quiescent supply
current due to the bias current needed for high-Z state
detection.
The MAX1617 also responds to the SMBus Alert Response
slave address (see the Alert Response Address section).
POR and UVLO
The MAX1617 has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the data in
memory and causing erratic behavior, a POR voltage
detector monitors VCC and clears the memory if VCC falls
below 1.7V (typical, see Electrical Characteristics table).
When power is first applied and VCC rises above 1.75V
(typical), the logic blocks begin operating, although reads
and writes at VCC levels below 3V are not recommended.
A second VCC comparator, the ADC UVLO comparator,
prevents the ADC from converting until there is sufficient
headroom (VCC = 2.8V typical).
www.maximintegrated.com
Table 9. Slave Address Decoding (ADD0
and ADD1)
ADD0
ADD1
ADDRESS
GND
GND
0011 000
GND
High-Z
0011 001
GND
VCC
0011 010
High-Z
GND
0101 001
High-Z
High-Z
0101 010
High-Z
VCC
0101 011
VCC
GND
1001 100
VCC
High-Z
1001 101
VCC
VCC
1001 110
Note: High-Z means that the pin is left unconnected.
Power-Up Defaults:
● Interrupt latch is cleared.
● Address select pins are sampled.
● ADC begins auto-converting at a 0.25Hz rate.
● Command byte is set to 00h to facilitate quick remote
Receive Byte queries.
● THIGH and TLOW registers are set to max and min
limits, respectively.
Maxim Integrated │ 14
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
A
tLOW
B
tHIGH
C
E
D
F
G
H
I
J
K
M
L
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tHD:DAT
tSU:STO tBUF
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Figure 4. SMBus Write Timing Diagram
A
tLOW
B
C
tHIGH
D
E
F
G
H
J
I
K
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:STO
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
tBUF
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
Figure 5. SMBus Read Timing Diagram
Programming Example:
Clock-Throttling Control for CPUs
An untested example of pseudocode for proportional
temperature control of Intel mobile CPUs via a powermanagement microcontroller is given in Listing 1. This
program consists of two main parts: an initialization
routine and an interrupt handler. The initialization routine
checks for SMBus communications problems and sets
up the MAX1617 configuration and conversion rate. The
interrupt handler responds to ALERT signals by reading
the current temperature and setting a CPU clock duty
www.maximintegrated.com
factor proportional to that temperature. The relationship
between clock duty and temperature is fixed in a lookup
table contained in the microcontroller code.
Note: Thermal management decisions should be made
based on the latest temperature obtained from the
MAX1617 rather than the value of the Status Byte. The
MAX1617 has a very quick response to changes in its
environment due to its sensitivity and its small thermal
mass. High and low alarm conditions can exist in the
Status Byte due to the MAX1617 correctly reporting environmental changes around it.
Maxim Integrated │ 15
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Listing 1. Pseudocode Example
www.maximintegrated.com
Maxim Integrated │ 16
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Listing 1. Pseudocode Example (continued)
www.maximintegrated.com
Maxim Integrated │ 17
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Listing 1. Pseudocode Example (continued)
www.maximintegrated.com
Maxim Integrated │ 18
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Package Information
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.
16 QSOP
E116+1
21-0055
90-0167
www.maximintegrated.com
Maxim Integrated │ 19
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
2
11/12
Updated Electrical Characteristics tables (added new Note 1); updated ADC and
Multiplexer and Remote-Diode Selection sections
3
11/16
Removed 200Ω resistor from Typical Operating Circuit
DESCRIPTION
2–4, 6, 8
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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