MAX6695AUB-T ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceApplicationsALERT INTERRUPT MAX6695TO μPNotebook ComputersTO CLOCKOT1DXNTHROTTLINGDesktop Computers ..
MAX6695YAUB+ ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceApplicationsALERT INTERRUPT MAX6695TO μPNotebook ComputersTO CLOCKOT1DXNTHROTTLINGDesktop Computers ..
MAX6696AEE ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceApplications DXNTHROTTLINGTO SYSTEMOT2Notebook ComputersSHUTDOWNDesktop ComputersServers DXP2GNDWor ..
MAX6696AEE ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceFeaturesThe MAX6695/MAX6696 are precise, dual-remote, and♦ Measure One Local and Two Remotelocal di ..
MAX6696AEE+ ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceELECTRICAL CHARACTERISTICS(V = +3.0V to +3.6V, T = 0°C to +125°C, unless otherwise noted. Typical v ..
MAX6696AEE+ ,Dual Remote/Local Temperature Sensors with SMBus Serial InterfaceMAX6695/MAX669619-3183; Rev 3; 4/11Dual Remote/Local Temperature Sensors withSMBus Serial Interface
MB3771PF-G-BND-JNE1 , ASSP For power supply applications BIPOLAR Power Supply Monitor
MB3771PS ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MB3771PS ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MB3773 ,Power Supply Monitor with Watch-Dog TimerFUJITSU SEMICONDUCTORDS04-27401-4EDATA SHEETASSPPower Supply Monitor with Watch-Dog TimerMB3773n DE ..
MB3775 ,SWITCHING REGULATOR CONTROLLERFUJITSU SEMICONDUCTORDS04-27204-3EDATA SHEETASSPSWITCHING REGULATOR CONTROLLERMB3775LOW VOLTAGE DUA ..
MB3775PF , SWITCHING REGULATOR CONTROLLER
MAX6695AUB+-MAX6695AUB+T-MAX6695AUB-T-MAX6695YAUB+-MAX6696AEE+-MAX6696AEE+T-MAX6696YAEE+-MAX6696YAEE+T
Dual Remote/Local Temperature Sensors with SMBus Serial Interface
General DescriptionThe MAX6695/MAX6696 are precise, dual-remote, and
local digital temperature sensors. They accurately mea-
sure the temperature of their own die and two remote
diode-connected transistors, and report the tempera-
ture in digital form on a 2-wire serial interface. The
remote diode is typically the emitter-base junction of a
common-collector PNP on a CPU, FPGA, GPU, or ASIC.
The 2-wire serial interface accepts standard system
management bus (SMBus) commands such as Write
Byte, Read Byte, Send Byte, and Receive Byte to read
the temperature data and program the alarm thresholds
and conversion rate. The MAX6695/MAX6696 can func-
tion autonomously with a programmable conversion
rate, which allows control of supply current and temper-
ature update rate to match system needs. For conver-
sion rates of 2Hz or less, the temperature is
represented as 10 bits + sign with a resolution of
+0.125°C. When the conversion rate is 4Hz, output data
is 7 bits + sign with a resolution of +1°C. The MAX6695/
MAX6696 also include an SMBus timeout feature to
enhance system reliability.
Remote temperature sensing accuracy is ±1.5°C be-
tween +60°C and +100°C with no calibration needed.
The MAX6695/MAX6696 measure temperatures from
-40°C to +125°C. In addition to the SMBus ALERTout-
put, the MAX6695/MAX6696 feature two overtempera-
ture limit indicators (OT1and OT2), which are active
only while the temperature is above the corresponding
programmable temperature limits. The OT1and OT2
outputs are typically used for fan control, clock throt-
tling, or system shutdown.
The MAX6695 has a fixed SMBus address. The
MAX6696 has nine different pin-selectable SMBus
addresses. The MAX6695 is available in a 10-pin
μMAX®and the MAX6696 is available in a 16-pin QSOP
package. Both operate throughout the -40°C to +125°C
temperature range.
ApplicationsNotebook Computers
Desktop Computers
Servers
Workstations
Test and Measurement Equipment
FeaturesMeasure One Local and Two Remote
Temperatures11-Bit, +0.125°C Resolution High Accuracy ±1.5°C (max) from +60°C to +100°C
(Remote)ACPI CompliantProgrammable Under/Overtemperature AlarmsProgrammable Conversion Rate Three Alarm Outputs: ALERT, OT1, and OT2SMBus/I2C-Compatible InterfaceCompatible with 65nm Process Technology
(Y Versions)
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
Ordering Information
Typical Operating Circuit19-3183; Rev 3; 4/11
PART TEMP RANGE PIN-PACKAGE
MAX6695AUB+ -40°C to +125°C 10 μMAX MAX6695YAUB+ -40°C to +125°C 10 μMAX
MAX6696AEE+ -40°C to +125°C 16 QSOP MAX6696YAEE+ -40°C to +125°C 16 QSOP
Devices are also available in tape-and-reel packages. Specify
tape and reel by adding “T” to the part number when ordering.
+Denotes a lead(Pb)-free/RoHS-compliant package.
Pin Configurations appear at end of data sheet.CLOCK
DATA
TO SYSTEM
SHUTDOWN
GND
OT2
SMBCLK
OT1
SMBDATA
VCC
INTERRUPT
TO μP
0.1μF
DXN
DXP1
47Ω
10kΩ
EACH
ALERT
+3.3V
CPU
TO CLOCK
THROTTLING
DXP2
GRAPHICS
PROCESSOR
MAX6695
Typical Operating Circuits continued at end of data sheet.
μMAX is a registered trademark of Maxim Integrated Products, Inc.
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
ABSOLUTE MAXIMUM RATINGSStresses 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.
VCC...........................................................................-0.3V to +6V
DXP1, DXP2................................................-0.3V to (VCC+ 0.3V)
DXN ......................................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT...................................-0.3V to +6V
RESET, STBY, ADD0, ADD1, OT1, OT2...................-0.3V to +6V
SMBDATA Current .................................................1mA to 50mA
DXN Current ......................................................................±1mA
Continuous Power Dissipation (TA= +70°C)
10-Pin μMAX (derate 6.9mW/°C above +70°C)........555.6mW
16-Pin QSOP (derate 8.3mW/°C above +70°C) .......666.7mW
Operating Temperature Range.........................-40°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
ELECTRICAL CHARACTERISTICS(VCC= +3.0V to +3.6V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V and TA= +25°C)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS Supply Voltage VCC 3.0 3.6 V
Standby Supply Current SMBus static, ADC in idle state 10 μA
Operating Current Interface inactive, ADC active 0.5 1 mA
Conversion rate = 0.125Hz 35 70
Conversion rate = 1Hz 250 500 Average Operating Current
Conversion rate = 4Hz 500 1000
μA
TRJ = +25°C to +100°C
(TA = +45°C to +85°C) -1.5 +1.5
TRJ = 0°C to +125°C (TA = +25°C to +100°C) -3.0 +3.0
TRJ = -40°C to +125°C (TA = 0°C to +125°C) -5.0 +5.0
Remote Temperature Error
(Note 1)
TRJ = -40°C to +125°C (TA = -40°C) +3.0
°C
TA = +45°C to +85°C -2.0 +2.0
TA = +25°C to +100°C -3.0 +3.0
TA = 0°C to +125°C -4.5 +4.5 Local Temperature Error
TA = -40°C to +125°C +3.0
°C
TA = +45°C to +85°C -3.8
TA = +25°C to +100°C -4.0
TA = 0°C to +125°C -4.2
Local Temperature Error
(MAX6695Y/MAX6696Y)
TA = -40°C to +125°C -4.4
°C
Power-On Reset Threshold VCC, falling edge (Note 2) 1.3 1.45 1.6 V
POR Threshold Hysteresis 500 mV
Undervoltage Lockout Threshold UVLO Falling edge of VCC disables ADC 2.2 2.8 2.95 V
Undervoltage Lockout Hysteresis 90 mV
Channel 1 rate 4Hz, channel 2 / local rate
2Hz (conversion rate register 05h) 112.5 125 137.5
Conversion Time
Channel 1 rate 8Hz, channel 2 / local rate
4Hz (conversion rate register 06h) 56.25 62.5 68.75
ms
High level 80 100 120 Remote-Diode Source Current IRJ
Low level 8 10 12
μA
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3.0V to +3.6V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= +3.3V and TA= +25°C)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS ALERT,OT1,OT2
Output Low Sink Current VOL = 0.4V 6 mA
Output High Leakage Current VOH = 3.6V 1 μA
INPUT PIN, ADD0, ADD1 (MAX6696) Logic Input Low Voltage VIL 0.3 V
Logic Input High Voltage VIH 2.9 V
INPUT PIN, RESET, STBY (MAX6696) Logic Input Low Voltage VIL 0.8 V
Logic Input High Voltage VIH 2.1 V
Input Leakage Current ILEAK -1 +1 μA
SMBus INTERFACE (SMBCLK, SMBDATA, STBY)Logic Input Low Voltage VIL 0.8 V
Logic Input High Voltage VIH 2.1 V
Input Leakage Current ILEAK VIN = GND or VCC ±1 μA
Output Low Sink Current IOL VOL = 0.6V 6 mA
Input Capacitance CIN 5 pF
SMBus-COMPATIBLE TIMING (Figures 4 and 5) (Note 2) Serial Clock Frequency fSCL 10 100 kHz
Bus Free Time Between STOP
and START Condition tBUF 4.7 μs
Repeat START Condition Setup
Time tSU:STA 90% of SMBCLK to 90% of SMBDATA 4.7 μs
START Condition Hold Time tHD:STA 10% of SMBDATA to 90% of SMBCLK 4 μs
STOP Condition Setup Time tSU:STO 90% of SMBCLK to 90% of SMBDATA 4 μs
Clock Low Period tLOW 10% to 10% 4 μs
Clock High Period tHIGH 90% to 90% 4.7 μs
Data Setup Time tSU:DAT 250 ns
Data Hold Time tHD:DAT 300 ns
SMB Rise Time tR 1 μs
SMB Fall Time tF 300 ns
SMBus Timeout SMBDATA low period for interface reset 20 30 40 ms
Note 1:Based on diode ideality factor of 1.008.
Note 2:Specifications are guaranteed by design, not production tested.
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
Typical Operating Characteristics(VCC= 3.3V, TA= +25°C, unless otherwise noted.)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGEMAX6695 toc01
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
AVERAGE OPERATING SUPPLY CURRENT
vs. CONVERSION RATE CONTROL REGISTER VALUE
MAX6695 toc02
CONVERSION RATE CONTROL REGISTER VALUE (hex)
OPERATING SUPPLY CURRENT (21
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6695 toc03
REMOTE TEMPERATURE (°C)
TEMPERATURE ERROR (
REMOTE CHANNEL2
REMOTE CHANNEL1
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATUREMAX6695 toc04
DIE TEMPERATURE (°C)
TEMPERATURE ERROR (
°C)
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6695 toc05
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (
°C)10100
REMOTE CHANNEL1
REMOTE CHANNEL2
TEMPERATURE ERROR
vs. DIFFERENTIAL NOISE FREQUENCY
MAX6695 toc06
FREQUENCY (MHz)
TEMPERATURE ERROR (
REMOTE CHANNEL1
VIN = 10mVP-P
REMOTE CHANNEL2
REMOTE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6695 toc07a
FREQUENCY (MHz)
TEMPERATURE ERROR (
100mVP-P
REMOTE CHANNEL2
REMOTE CHANNEL1
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6695 toc07b
FREQUENCY (MHz)
TEMPERATURE ERROR (
100mVP-P
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6695 toc08
FREQUENCY (Hz)
TEMPERATURE ERROR (
REMOTE CHANNEL1
10mVP-P
REMOTE CHANNEL2
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
Pin Description
PIN
MAX6695MAX6696NAMEFUNCTION1 2 VCC
Supply Voltage Input, +3V to +3.6V. Bypass to GND with a 0.1μF capacitor. A 47
series resistor is recommended but not required for additional noise filtering. See
Typical Operating Circuit.
2 3 DXP1
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode
Channel 1. DO NOT LEAVE DXP1 UNCONNECTED; connect DXP1 to DXN if no
remote diode is used. Place a 2200pF capacitor between DXP1 and DXN for noise
filtering.
3 4 DXN Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally
biased to one diode drop above ground.
4 5 DXP2
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode
Channel 2. DO NOT LEAVE DXP2 UNCONNECTED; connect DXP2 to DXN if no
remote diode is used. Place a 2200pF capacitor between DXP2 and DXN for noise
filtering.
5 10 OT1Overtemperature Active-Low Output, Open Drain. OT1 is asserted low only when
the temperature is above the programmed OT1 threshold.
6 8 GND Ground9 SMBCLK SMBus Serial-Clock Input
8 11 ALERT
SMBus Alert (Interrupt) Active-Low Output, Open-Drain. Asserts when temperature
exceeds user-set limits (high or low temperature) or when a remote sensor opens.
Stays asserted until acknowledged by either reading the status register or by
successfully responding to an alert response address. See the ALERTInterrupts
section.12 SMBDATA SMBus Serial-Data Input/Output, Open Drain
10 13 OT2Overtemperature Active-Low Output, Open Drain. OT2 is asserted low only when
temperature is above the programmed OT2 threshold.
— 1, 16 N.C. No Connect
— 6 ADD1 SMBus Slave Address Select Input (Table 10). ADD0 and ADD1 are sampled upon
power-up.
— 7 RESET Reset Input. Drive RESET high to set all registers to their default values (POR state).
Pull RESET low for normal operation.
— 14 ADD0 SMBus Slave Address Select Input (Table 10). ADD0 and ADD1 are sampled upon
power-up.
— 15 STBYHardware Standby Input. Pull STBY low to put the device into standby mode.
All registers’ data are maintained.
MAX6695/MAX6696
Detailed DescriptionThe MAX6695/MAX6696 are temperature sensors
designed to work in conjunction with a microprocessor
or other intelligence in temperature monitoring, protec-
tion, or control applications. Communication with the
MAX6695/MAX6696 occurs through the SMBus serial
interface and dedicated alert pins. The overtempera-
ture alarms OT1and OT2are asserted if the software-
programmed temperature thresholds are exceeded.
OT1and OT2can be connected to a fan, system shut-
down, or other thermal-management circuitry.
The MAX6695/MAX6696 convert temperatures to digital
data continuously at a programmed rate or by selecting
a single conversion. At the highest conversion rate,
temperature conversion results are stored in the “main”
temperature data registers (at addresses 00h and 01h)
as 7-bit + sign data with the LSB equal to +1°C. At
slower conversion rates, 3 additional bits are available
at addresses 11h and 10h, providing +0.125°C resolu-
tion. See Tables 2, 3, and 4 for data formats.
ADC and MultiplexerThe MAX6695/MAX6696 averaging ADC (Figure 1) inte-
grates over a 62.5ms or 125ms period (each channel,
typ), depending on the conversion rate (see Electrical
Characteristicstable). The use of an averaging ADC
attains excellent noise rejection.
The MAX6695/MAX6696 multiplexer (Figure 1) automat-
ically steers bias currents through the remote and local
diodes. The ADC and associated circuitry measure
each diode’s forward voltages and compute the tem-
perature based on these voltages. If a remote channel
is not used, connect DXP_ to DXN. Do not leave DXP_
and DXN unconnected.When a conversion is initiated,
all channels are converted whether they are used or
not. The DXN input is biased at one VBEabove ground
by an internal diode to set up the ADC inputs for a dif-
ferential measurement. Resistance in series with the
remote diode causes about +1/2°C error per ohm.
A/D Conversion SequenceA conversion sequence consists of a local temperature
measurement and two remote temperature measure-
ments. Each time a conversion begins, whether initiat-
ed automatically in the free-running autoconvert mode
(RUN/STOP = 0) or by writing a one-shot command, all
three channels are converted, and the results of the
three measurements are available after the end of con-
version. Because it is common to require temperature
measurements to be made at a faster rate on one of the
remote channels than on the other two channels, the
conversion sequence is Remote 1, Local, Remote 1,
double that of the conversion rate for either of the other
two channels.
A BUSY status bit in status register 1 (see Table 7 and
the Status Byte Functionssection) shows that the
device is actually performing a new conversion. The
results of the previous conversion sequence are always
available when the ADC is busy.
Remote-Diode SelectionThe MAX6695/MAX6696 can directly measure the die
temperature of CPUs and other ICs that have on-board
temperature-sensing diodes (see the Typical Operating
Circuit)or they can measure the temperature of a dis-
crete diode-connected transistor.
Effect of Ideality FactorThe accuracy of the remote temperature measurements
depends on the ideality factor (n) of the remote “diode”
(actually a transistor). The MAX6695/MAX6696 (not the
MAX6695Y/MAX6696Y) are optimized for n = 1.008. A
thermal diode on the substrate of an IC is normally a PNP
with its collector grounded. DXP_ must be connected to
the anode (emitter) and DXN must be connected to the
cathode (base) of this PNP.
If a sense transistor with an ideality factor other than
1.008 is used, the output data will be different from the
data obtained with the optimum ideality factor.
Fortunately, the difference is predictable. Assume a
remote-diode sensor designed for a nominal ideality
factor nNOMINALis used to measure the temperature of
a diode with a different ideality factor n1. The measured
temperature TMcan be corrected using:
where temperature is measured in Kelvin and
nNOMIMALfor the MAX6695/MAX6696 is 1.008.
As an example, assume you want to use the MAX6695
or MAX6696 with a CPU that has an ideality factor of
1.002. If the diode has no series resistance, the mea-
sured data is related to the real temperature as follows:
For a real temperature of +85°C (358.15K), the measured
temperature is +82.87°C (356.02K), an error of -2.13°C.
Effect of Series ResistanceSeries resistance (RS) with a sensing diode contributes
additional error. For nominal diode currents of 10μAnTACTUALMNOMINALM=×⎛⎜⎞⎟=×⎛1008002⎜⎜⎞⎟=×()TM100599.nMACTUALNOMINAL=×⎛⎜⎞⎟1
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
and 100μA, the change in the measured voltage due to
series resistance is:
Since 1°C corresponds to 198.6μV, series resistance
contributes a temperature offset of:
Assume that the sensing diode being measured has a
series resistance of 3Ω. The series resistance con-
tributes a temperature offset of:
The effects of the ideality factor and series resistance
are additive. If the diode has an ideality factor of 1.002
and series resistance of 3Ω, the total offset can be cal-
culated by adding error due to series resistance with
error due to ideality factor:
1.36°C - 2.13°C = -0.77°C
for a diode temperature of +85°C.0453136ΩΩ×°=+°..CC
1986453ΩΩ.°
ΔVAARARMSS=−×=×()1001090μμμ
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial InterfaceOT2
OT1
ALERT
DXP2
DXN
DXP1
RESET/
UVLO
CIRCUITRY
VCC(RESET)
MUX
REMOTE1
REMOTE2
LOCALSOT2 THRESHOLDS
ALERT RESPONSE ADDRESS
ALERT THRESHOLD
LOCAL TEMPERATURES
REMOTE TEMPERATURES
COMMAND BYTE
REGISTER BANKSS
ADCCONTROL
LOGIC
SMBus
READ
WRITE
(STBY)
SMBDATA
SMBCLK
(ADD0)
(ADD1)ADDRESS
DECODER
DIODE FAULT
() ARE FOR MAX6696 ONLY.
OT1 THRESHOLDS
Figure 1. MAX6695/MAX6696 Functional Diagram
MAX6695/MAX6696In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
Discrete Remote DiodesWhen the remote-sensing diode is a discrete transistor,
its collector and base must be connected together.
Table 1 lists examples of discrete transistors that are
appropriate for use with the MAX6695/MAX6696.
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage at
the highest expected temperature must be greater than
0.25V at 10μA, and at the lowest expected tempera-
ture, the forward voltage must be less than 0.95V at
100μA. Large power transistors must not be used. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < ß <150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
VBEcharacteristics.
Manufacturers of discrete transistors do not normally
specify or guarantee ideality factor. This is normally not
a problem since good-quality discrete transistors tend
to have ideality factors that fall within a relatively narrow
range. We have observed variations in remote tempera-
ture readings of less than ±2°C with a variety of dis-
crete transistors. Still, it is good design practice to
verify good consistency of temperature readings with
several discrete transistors from any manufacturer
under consideration.
Thermal Mass and Self-HeatingWhen sensing local temperature, these temperature
sensors are intended to measure the temperature of the
PC board to which they are soldered. The leads pro-
vide a good thermal path between the PC board traces
and the die. As with all IC temperature sensors, thermal
conductivity between the die and the ambient air is
poor by comparison, making air temperature measure-
ments impractical. Because the thermal mass of the PC
board is far greater than that of the MAX6695/
MAX6696, the device follows temperature changes on
the PC board with little or no perceivable delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtu-
ally no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote
transistors, the best thermal response times are
obtained with transistors in small packages (i.e., SOT23
or SC70). 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.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For local temperature mea-
surements, the worst-case error occurs when autocon-
verting at the fastest rate and simultaneously sinking
maximum current at the ALERToutput. For example,
with VCC= 3.6V, a 4Hz conversion rate and ALERT
sinking 1mA, the typical power dissipation is:
θJ-Afor the 16-pin QSOP package is about +120°C/W,
so assuming no copper PC board heat sinking, the
resulting temperature rise is:
Even under these worst-case circumstances, it is diffi-
cult to introduce significant self-heating errors.
ADC Noise FilteringThe integrating ADC has good noise rejection for low-
frequency signals such as power-supply hum. In envi-
ronments with significant high-frequency EMI, connect
an external 2200pF capacitor between DXP_ and DXN.
Larger capacitor values can be used for added filter-
ing, but do not exceed 3300pF because it can intro-
duce errors due to the rise time of the switched current
source. High-frequency noise reduction is needed for
high-accuracy remote measurements. Noise can be
reduced with careful PC board layout as discussed in
the PC Board Layoutsection.
Low-Power Standby ModeStandby mode reduces the supply current to less than
10μA by disabling the ADC. Enter hardware standby
(MAX6696 only) by forcing STBYlow, or enter software
standby by setting the RUN/STOP bit to 1 in the config-
ΔTmWCWC=×°=+°221200264./.VmAmWCC×+×=50004122μ..
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
MANUFACTURERMODEL NO.Central Semiconductor (USA)CMPT3904
Rohm Semiconductor (USA)SST3904
Samsung (Korea)KST3904-TF
Siemens (Germany)SMBT3904
Zetex (England)FMMT3904CT-ND
Table 1. Remote-Sensor Transistor
Manufacturers
Note:Discrete transistors must be diode connected (base
shorted to collector).
uration byte register. Hardware and software standbys
are very similar; all data is retained in memory, and the
SMBus interface is alive and listening for SMBus com-
mands but the SMBus timeout is disabled. The only dif-
ference is that in software standby mode, the one-shot
command initiates a conversion. With hardware stand-
by, the one-shot command is ignored. Activity on the
SMBus causes the device to draw extra supply current.
Driving STBYlow overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the con-
version cycle is interrupted, and the temperature regis-
ters are not updated. The previous data is not changed
and remains available.
SMBus Digital InterfaceFrom a software perspective, the MAX6695/MAX6696
appear as a series of 8-bit registers that contain tem-
perature data, alarm threshold values, and control bits.
A standard SMBus-compatible 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. The same SMBus slave
address provides access to all functions.
The MAX6695/MAX6696 employ four standard SMBus
protocols: Write Byte, Read Byte, Send Byte, and
Receive Byte (Figure 2). The shorter Receive Byte proto-
col allows quicker transfers, provided that the correct
data register was previously selected by a Read Byte
instruction. Use caution with the shorter protocols in mul-
timaster systems, since a second master could overwrite
the command byte without informing the first master.
When the conversion rate control register is set ≥06h,
temperature data can be read from the read internal
temperature (00h) and read external temperature (01h)
registers. The temperature data format in these regis-
ters is 7 bits + sign in two’s-complement form for each
channel, with the LSB representing +1°C (Table 2). The
MSB is transmitted first. Use bit 3 of the configuration
register to select the registers corresponding to remote
1 or remote 2.
When the conversion rate control register is set ≤05h,
temperature data can be read from the read internal
temperature (00h) and read external temperature (01h)
registers, the same as for faster conversion rates. An
additional 3 bits can be read from the read external
extended temperature register (10h) and read internal
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial InterfaceFigure 2. SMBus Protocols
ACK7 bits
ADDRESSACKWR8 bits
DATAACK8 bits
COMMAND
Write Byte Format
Read Byte Format
Send Byte FormatReceive Byte FormatSlave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
ACK7 bits
ADDRESSACKWRSACK8 bits
DATA7 bits
ADDRESSRD8 bits
///PCOMMANDSlave Address: equiva-
lent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
ACK7 bits
ADDRESSWR8 bits
COMMANDACKPACK7 bits
ADDRESSRD8 bits
DATA///PSCommand Byte: sends com-
mand with no data, usually
used for one-shot command
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
S = Start conditionShaded = Slave transmission
P = Stop condition/// = Not acknowledged
MAX6695/MAX6696extended temperature register (11h) (Table 3), which
extends the temperature data to 10 bits + sign and the
resolution to +0.125°C per LSB (Table 4).
When a conversion is complete, the main register and
the extended register are updated almost simultane-
ously. Ensure that no conversions are completed
between reading the main and extended registers so
that when data that is read, both registers contain the
result of the same conversion.
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:Put the MAX6695/MAX6696 into standby mode by
setting bit 6 of the configuration register to 1. Read
the contents of the data registers. Return to run
mode by setting bit 6 to zero.Put the MAX6695/MAX6696 into standby mode by
setting bit 6 of the configuration register to 1. Initiate
a one-shot conversion using Send Byte command
0Fh. When this conversion is complete, read the
contents of the temperature data registers.
Diode Fault AlarmThere is a continuity fault detector at DXP_ that detects
an open circuit between DXP_ and DXN, or a DXP_
short to VCC, GND, or DXN. If an open or short circuit
exists, the external temperature register (01h) is loaded
with 1000 0000. Bit 2 (diode fault) of the status registers
is correspondingly set to 1. The ALERToutput asserts
for open diode faults but not for shorted diode faults.
Immediately after power-on reset (POR), the status reg-
ister indicates that no fault is present until the end of
the first conversion. After the conversion is complete,
any diode fault is indicated in the appropriate status
register. Reading the status register clears the diode
fault bit in that register, and clears the ALERToutput if
set. If the diode fault is present after the next conver-
sion, the status bit will again be set and the ALERTout-
put will assert if the fault is an open diode fault.
Alarm Threshold RegistersSix registers, WLHO, WLLM, WRHA (1 and 2), and
WRLN (1 and 2), store ALERTthreshold values. WLHO
and WLLM, are for internalALERThigh-temperature
and low-temperature limits, respectively. Likewise,
WRHA and WRLN are for externalchannel 1 and chan-
nel 2 high-temperature and low-temperature limits,
respectively (Table 5). If either measured temperature
equals or exceeds the corresponding ALERTthreshold
value, the ALERToutput is asserted.The POR state of
both internal and external ALERThigh-temperature limit
registers is 0100 0110 or +70°C.
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
TEMP (°C)DIGITAL OUTPUT+130.000 111 1111
+127.000 111 1111
+126.000 111 1110
+25.250 001 1001
+0.500 000 00010 000 00001 111 1111
-551 100 1001
Diode fault
(short or open)1 000 0000
Table 2. Data Format (Two’s Complement)
FRACTIONAL
TEMPERATURE (°C)
CONTENTS OF
EXTENDED REGISTER000X XXXX
+0.125001X XXXX
+0.250010X XXXX
+0.375011X XXXX
+0.500100X XXXX
+0.625101X XXXX
+0.750110X XXXX
+0.875111X XXXX
Table 3. Extended Resolution Register
Note:Extended resolution applies only for conversion rate
control register values of 05h or less.
TEMP (°C)INTEGER TEMPFRACTIONAL TEMP+130.000 111 1111000X XXXX
+127.000 111 1111000X XXXX
+126.50 111 1110100X XXXX
+25.250 001 1001010X XXXX
+0.500 000 0000100X XXXX0 000 0000000X XXXX1 111 1111000X XXXX
-1.251111 1111010X XXXX
-551100 1001000X XXXX
Table 4. Data Format in Extended Mode
