19-2305; Rev 1; 1/05
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
The MAX6680/MAX6681 are precise, two-channel digi-
tal thermometers. Each accurately measures the tem-
perature of its own die and one remote PN junction and
reports the temperature on a 2-wire serial interface. The
remote junction can be a diode-connected transistor
like the low-cost NPN type 2N3904 or PNP type
2N3906. The remote junction can also be a common-
collector PNP, such as a substrate PNP of a micro-
The MAX6680/MAX6681 include pin-programmable
default temperature thresholds for the OVERT output,
which provides fail-safe clock throttling or system shut-
down. In addition, the devices are pin programmable to
select whether the OVERT output responds to either the
local, remote, or both temperatures.
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 MAX6680/MAX6681 can func-
tion autonomously with a programmable conversion
rate, which allows the control of supply current and
temperature update rate to match system needs. For
conversion rates of 4Hz or less, the remote sensor tem-
perature can be represented in extended mode as 10
bits + sign with a resolution of 0.125°C. When the con-
version rate is 8Hz, output data is 7 bits + sign with a
resolution of 1°C. The MAX6680/MAX6681 also include
an SMBus timeout feature to enhance system reliability.
The MAX6681 is an upgrade to the MAX6654. The
MAX6680/MAX6681 remote accuracy is ±1°C with no
calibration needed. They are available in a 16-pin
QSOP package and operate throughout the -55°C to
+125°C temperature range.
Pin Configurations appear at end of data sheet.
♦ Two Alarm Outputs: ALERT and OVERT
♦ Pin-Programmable Threshold for OVERT Limit
♦ Programmable Under/Overtemperature ALERT
♦ Dual Channel: Measures Remote and Local
♦ 11-Bit, 0.125°C Resolution for Remote Temperature
♦ High Accuracy ±1°C (max) from +60°C to +100°C
♦ No Calibration Required
♦ SMBus/I2C™-Compatible Interface
♦ SMBus Timeout Prevents SMBus Lockup
-55°C to +125°C
-55°C to +125°C
Typical Operating Circuit
DXP VCC STBY
ADD1 GND CRIT0 CRIT1
SMBus is a trademark of Intel Corp.
I2C is a trademark of Philips Corp.
________________________________________________________________ Maxim Integrated Products 1
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