19-1836; Rev 2; 1/02
1°C Accurate Remote/Local Temperature
Sensor with SMBus Serial Interface
General Description
The MAX6654
?
is a precise digital thermometer that
reports the temperature of both a remote P-N junction
and its own die. The remote junction can be a diode-con-
nected transistor—typically a low-cost, easily mounted
2N3904 NPN type or 2N3906 PNP type—that replaces
conventional thermistors or thermocouples. Remote
accuracy is ±1°C for multiple transistor manufacturers,
with no calibration needed. The remote junction can also
be a common-collector PNP, such as a substrate PNP of
a microprocessor (μP).
The 2-wire serial interface accepts standard System
Management Bus (SMBus)
TM
, Write Byte, Read Byte,
Send Byte, and Receive Byte commands to program the
alarm thresholds and to read temperature data.
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 conversion rate allows the user to
optimize supply current and temperature update rate to
match system needs. When the conversion rate is faster
than 1Hz, the conversion results are available as a 7-bit-
plus-sign byte with a 1°C LSB. When the conversion rate
is 1Hz or slower, the MAX6654 enters the extended
mode. In this mode, 3 additional bits of temperature data
are available in the extended resolution register, provid-
ing 10-bit-plus-sign resolution with a 0.125°C LSB.
Single-shot conversions also have 0.125°C per LSB reso-
lution when the conversion rate is 1Hz or slower.
A parasitic resistance cancellation (PRC) mode can also
be invoked for conversion rates of 1Hz or slower by set-
ting bit 4 of the configuration register to 1. In PRC mode,
the effect of series resistance on the leads of the external
diode is canceled. The 11-bit conversion in PRC mode is
performed in <500ms and is disabled for conversion
rates faster than 1Hz. The one-shot conversion is also 11
bits in <500ms.
The MAX6654 default low-temperature measurement
limit is 0°C. This can be extended to -64°C by setting bit
5 of the configuration register to 1.
The MAX6654 is available in a small, 16-pin QSOP sur-
face-mount package.
Features
o
High Accuracy ±1°C (max) from 70°C to 100°C
(Remote)
o
11-Bit, 0.125°C Resolution
o
Dual Channel: Measures Remote and Local
Temperature
o
No Calibration Required
o
Programmable Under/Overtemperature Alarms
o
I
2
C?-Compatible/SMBus Interface
o
3V to 5.5V Supply Range
MAX6654
Ordering Information
PART
MAX6654MEE
TEMP. RANGE
-55°C to 125°C
PIN-PACKAGE
16 QSOP
Typical Operating Circuit
0.1μF
200?
3V TO 5V SUPPLY
CPU
V
CC
STBY
DXP
MAX6654
SMBCLK
SMBDATA
10k EACH
CLOCK
DATA
2200pF
DXN
ADD0 ADD1
ALERT
GND
INTERRUPT TO
μC
Pin Configuration
TOP VIEW
N.C. 1
V
CC
2
DXP 3
DXN 4
N.C. 5
ADD1 6
GND 7
GND 8
16 N.C.
15 STBY
14 SMBCLK
________________________Applications
Desktop Computers
Notebook Computers
Servers
Thin Clients
Workstations
Test and Measurement
Multichip Modules
MAX6654
13 N.C.
12 SMBDATA
11 ALERT
10 ADD0
9
N.C.
SMBus is a trademark of Intel Corp.
I
2
C is a trademark of Philips Corp.
?
Patents pending
QSOP
_______________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.