MAXIM MAX6682 User Manual
General Description
The MAX6682 converts an external thermistor’s temperature-dependent resistance directly into digital form.
The thermistor and an external fixed resistor form a voltage-divider that is driven by the MAX6682’s 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 coefficient (NTC) thermistor, but it does provide linear output data over limited temperature ranges when used
with an external resistor of the correct value. Over the
0° to +50°C temperature range, the MAX6682 produces
output data that is scaled to 8LSBs/°C (for 0.125°C resolution), provided that the correct thermistor and external 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™-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 thermistor current, minimizing self-heating. Between conversions, supply current is reduced to 21µA (typ). The
internal voltage reference is shut down between measurements.
The MAX6682 is available in a small, 8-pin µMAX package and is specified over the -55°C to +125°C temperature range.
Applications
HVAC
Medical Devices
Battery Packs/Chargers
Home Appliances
Features
♦ Converts Thermistor Temperature to Digital Data
♦ Low Average Thermistor Current Minimizes Self-
Heating Errors
♦ Low Supply Current, 21µA (typ) Including 10kΩ
Thermistor Current
♦ Internal Voltage Reference Isolates Thermistor
from Power-Supply Noise
♦ 10-Bit Resolution
♦ Accommodates Any Thermistor Temperature
Range
♦ Output Data Scaled for Direct Temperature
Readings from 0°C to +50°C
♦ Simple SPI-Compatible Interface
♦ Small, 8-Pin µMAX Package
MAX6682
Thermistor-to-Digital Converter
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2219; Rev 0; 2/02
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.
SPI is a trademark of Motorola, Inc.
Pin Configuration appears at end of data sheet.
3.3V
0.1µF
MC68HCXX
I/O
SCLK
MISO
CS
SCLK
SO
V
CC
R+
R-
GND
MAX6682
R
EXT
THERMISTOR
Typical Operating Circuit
PART TEMP RANGE PIN-PACKAGE
MAX6682MUA -55°C to +125°C 8 µMAX
MAX6682
Thermistor-to-Digital Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= 3V to 5.5V, TA= -55°C to +125°C, unless otherwise noted. Typical values are specified at VCC= 3.3V and TA= +25°C.) (Note 1)
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.
Supply Voltage (VCCto GND) .................................-0.3V to +6V
SO, SCK, CS, R-, R+ to GND ....................-0.3V to (V
CC
+ 0.3V)
R+ Current ........................................................................±20mA
R- Current ...........................................................................±1mA
SCK, CS, SO Current .........................................-1mA to +50mA
ESD Protection (Human Body Model) .............................±2000V
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (derate 4.1mW/°C above +70°C) ............ 328mW
Operating Temperature Range
(T
MIN
to T
MAX
) ...............................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature .....................................................+150°C
Supply Voltage V
ADC Total Unadjusted Error TUE
ADC Conversion Time t
R- Input Impedance Z
R- Leakage Current 150nA
Conversion Rate 0.5 Hz
Reference Voltage Output V
Reference Load Regulation 0 < I
Reference Supply Regulation 0.7 mV/V
Conversion Supply Current I
Average Supply Current I
Standby Current I
Idle Current I
SERIAL INTERFACE
Input Low Voltage V
Input High Voltage V
Input Leakage Current I
Output High Voltage V
Output Low Voltage V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CC
CONV
IN
REF
C
A
S
ID
IL
IH
LEAK
OH
OL
DOUT = 768.935 x (V
> 0.1V
V
IN
I
LOAD
REF
= 1mA 1.10 1.22 1.40 V
< 2mA 0 0.1 %/mA
LOAD
REXT/VR+
During conversion, no load 220 300 µA
0.5 conversions/s, no load 17 29 µA
CS low, SCK inactive 3 7 µA
CS high, analog circuits off 10 17 µA
VIN = GND or V
I
SOURCE
I
= 1.6mA 0.4 V
SINK
CC
= 1.6mA
) - 134.0923;
3.0 5.5 V
-3 +3 LSB
64 80 ms
1MΩ
0.2 x
V
CC
0.8 x
V
CC
1µA
V
-
CC
0.4
V
V
V
MAX6682
Thermistor-to-Digital Converter
_______________________________________________________________________________________ 3
TIMING CHARACTERISTICS
(VCC= 3V to 5.5V, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical values are specified at VCC= 3.3V and TA= +25°C.) (Note 2)
Note 1: All specifications are 100% tested at T
A
= +25°C. Specification limits over temperature are guaranteed by design,
not production tested.
Note 2: Guaranteed by design.
Typical Operating Characteristics
(VCC= 5V, thermistor = 10k nominal, R
EXT
= 7680Ω, TA = +25°C, unless otherwise noted.)
0
0.3
0.2
0.1
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0105152025
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6682 toc01
FREQUENCY (MHz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
APPLIED TO V
CC
WITH
NO V
CC
BYPASS CAPACITOR
VIN = 250mV
P-P
40
60
50
80
70
90
100
1k 100k10k 1M 10M
AVERAGE SUPPLY CURRENT
vs. CLOCK FREQUENCY
MAX6682 toc02
SCK FREQUENCY (Hz)
SUPPLY CURRENT (µA)
SCK IS DRIVEN
RAIL-TO-RAIL
®
30
50
40
70
60
90
80
100
3.0 4.03.5 4.5 5.0 5.5
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6682 toc03
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SERIAL INTERFACE TIMING (Figures 5 and 6)
Serial Clock Frequency f
SCK Pulse High Width t
SCK Pulse Low Width t
CS Fall to SCK Rise t
CS Fall to Output Data Valid t
SCK Fall to Output Data Valid t
CS Rise to Output High-Z t
SCK Fall to Output High-Z t
CS Pulse Width t
SCL
CH
CL
CSS
DV
DO
TR
HIZ
CSW
5 MHz
50 ns
50 ns
35 ns
CL = 10pF 35 ns
CL = 10pF 35 ns
CL = 10pF 25 ns
CL = 10pF 35 ns
75 ns
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