19-2219; Rev 0; 2/02
Thermistor-to-Digital Converter
General Description
The MAX6682 converts an external thermistor鈥檚 temper-
ature-dependent resistance directly into digital form.
The thermistor and an external fixed resistor form a volt-
age-divider that is driven by the MAX6682鈥檚 internal
voltage reference. The MAX6682 measures the voltage
across the external resistor and produces a 10-bit +
sign output code dependent on that voltage.
The MAX6682 does not linearize the highly nonlinear
transfer function of a typical negative temperature coef-
ficient (NTC) thermistor, but it does provide linear out-
put data over limited temperature ranges when used
with an external resistor of the correct value. Over the
0掳 to +50掳C temperature range, the MAX6682 produces
output data that is scaled to 8LSBs/掳C (for 0.125掳C res-
olution), provided that the correct thermistor and exter-
nal resistor values are used. Other temperature ranges
can be easily accommodated, but do not necessarily
yield data scaled to an even number of LSBs per
degree.
The 3-wire SPI鈩?compatible interface can be readily
connected to a variety of microcontrollers.
The MAX6682 is a read-only device, simplifying use in
systems where only temperature data is required.
Power-management circuitry reduces the average ther-
mistor current, minimizing self-heating. Between con-
versions, supply current is reduced to 21碌A (typ). The
internal voltage reference is shut down between mea-
surements.
The MAX6682 is available in a small, 8-pin 碌MAX pack-
age and is specified over the -55掳C to +125掳C temper-
ature range.
Features
o
Converts Thermistor Temperature to Digital Data
o
Low Average Thermistor Current Minimizes Self-
Heating Errors
o
Low Supply Current, 21碌A (typ) Including 10k鈩?/div>
Thermistor Current
o
Internal Voltage Reference Isolates Thermistor
from Power-Supply Noise
o
10-Bit Resolution
o
Accommodates Any Thermistor Temperature
Range
o
Output Data Scaled for Direct Temperature
Readings from 0掳C to +50掳C
o
Simple SPI-Compatible Interface
o
Small, 8-Pin 碌MAX Package
MAX6682
Ordering Information
PART
MAX6682MUA
TEMP RANGE
-55掳C to +125掳C
PIN-PACKAGE
8 碌MAX
Typical Operating Circuit
3.3V
Applications
HVAC
Medical Devices
Battery Packs/Chargers
Home Appliances
R+
R
EXT
0.1碌F
V
CC
MAX6682
R-
MC68HCXX
CS
SCLK
GND
SO
I/O
SCLK
MISO
Pin Configuration appears at end of data sheet.
THERMISTOR
SPI is a trademark of Motorola, Inc.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim鈥檚 website at www.maxim-ic.com.
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