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PDF MAX6682 Data sheet ( Hoja de datos )
| Número de pieza | MAX6682 | |
| Descripción | Thermistor-to-Digital Converter | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-2219; Rev 0; 2/02
Thermistor-to-Digital Converter
General Description
The MAX6682 converts an external thermistor’s 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’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 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° to +50°C temperature range, the MAX6682 produces
output data that is scaled to 8LSBs/°C (for 0.125°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™-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 21µA (typ). The
internal voltage reference is shut down between mea-
surements.
The MAX6682 is available in a small, 8-pin µMAX pack-
age and is specified over the -55°C to +125°C temper-
ature range.
HVAC
Medical Devices
Battery Packs/Chargers
Home Appliances
Applications
Pin Configuration appears at end of data sheet.
SPI is a trademark of Motorola, Inc.
Features
o Converts Thermistor Temperature to Digital Data
o Low Average Thermistor Current Minimizes Self-
Heating Errors
o Low Supply Current, 21µA (typ) Including 10kΩ
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°C to +50°C
o Simple SPI-Compatible Interface
o Small, 8-Pin µMAX Package
PART
MAX6682MUA
Ordering Information
TEMP RANGE
-55°C to +125°C
PIN-PACKAGE
8 µMAX
Typical Operating Circuit
3.3V
0.1µF
VCC
REXT
THERMISTOR
R+
MAX6682
R-
CS
SCLK
GND SO
MC68HCXX
I/O
SCLK
MISO
________________________________________________________________ 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.
1 page  
Thermistor-to-Digital Converter
Table 1. Temperature vs. Digital Output for Standard Thermistor with REXT = 7680Ω
THERMISTOR
TEMPERATURE (°C)
+60.000
+50.000
+40.000
+30.000
+25.000
+20.000
+10.000
0
-0.725
-2.000
-5.000
*Assumes VR+ = 1.220V.
VREXT (mV) WITH STANDARD
THERMISTOR AND REXT =
7680Ω*
921.6
830.6
720.5
595.4
530.1
464.4
339.7
232.3
225.5
213.6
187.4
DECIMAL VALUE OF DOUT
(1LSB = 0.125°C)
+55.875
+48.625
+40.000
+30.125
+25.000
+19.875
+10.000
+1.500
+1.000
0.125
-2.000
DOUT
001 1011 1111
001 1000 0101
001 0100 0000
000 1111 0001
000 1100 1000
000 1001 1111
000 0101 0000
000 0000 1100
000 0000 1000
000 0000 0001
111 1111 0000
NTC thermistor is very nonlinear and can be described
by the following approximation:
1 / T = A + BlnR + C(lnR)3
where T is absolute temperature, R is the thermistor’s
resistance, and A, B, and C are coefficients that vary
with manufacturer and material characteristics. The
general shape of the curve is shown in Figure 1.
The highly nonlinear relationship between temperature
and resistance in an NTC thermistor makes it somewhat
more difficult to use than a digital-output temperature
sensor IC, for example. However, by connecting the
thermistor in series with a properly chosen resistor and
using the MAX6682 to measure the voltage across the
resistor, a reasonably linear transfer function can be
obtained over a limited temperature range. Errors
decrease for smaller temperature ranges.
Figures 2 and 3 show typical thermistor nonlinearity
curves for a standard thermistor in conjunction with
series resistors chosen to optimize linearity over two
different temperature ranges: +10°C to +40°C and 0°C
to +70°C.
THERMISTOR RESISTANCE
vs. TEMPERATURE
120
100
80
60
40
20
0
-40 -20
0 20 40 60 80 100 120
TEMPERATURE (°C)
3.0
2.5
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
-2.0
-2.5
0
THERMISTOR NONLINEARITY
vs. TEMPERATURE
10 20 30 40 50 60 70
TEMPERATURE (°C)
80
Figure 1. Thermistor Resistance vs. Temperature
Figure 2. Thermistor Nonlinearity vs. Temperature for a Standard
Thermistor from 0°C to +70°C
_______________________________________________________________________________________ 5
5 Page | ||
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| PDF Descargar | [ Datasheet MAX6682.PDF ] | |
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