MAX6682MUA+ Maxim Integrated Products, MAX6682MUA+ Datasheet - Page 6

• Manufacturer Part Number: MAX6682MUA+
• Description: IC THERMISTOR TO DGTL 8UMAX
• Manufacturer: Maxim Integrated Products
• Type: Temperature Sensorr

Specifications of MAX6682MUA+

• Input Type: Logic
• Output Type: Logic
• Interface: 3-Wire SPI Serial
• Current - Supply: 29µA
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Full Temp Accuracy: +/- 0.5 C
• Digital Output - Bus Interface: 3-Wire, SPI
• Digital Output - Number Of Bits: 10 bit
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• Supply Current: 21 uA
• Ic Output Type: Digital
• Sensing Accuracy Range: ± 0.5°C
• Temperature Sensing Range: -55°C To +125°C
• Supply Voltage Range: 3V To 5.5V
• Resolution (bits): 10bit
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

NTC thermistors are often described by the resistance
at +25°C. Therefore, a 10kΩ thermistor has a resistance
of 10kΩ at +25°C. When choosing a thermistor, ensure
that the thermistor’s minimum resistance (which occurs
at the maximum expected operating temperature) in
series with R
output current to exceed about 1mA. Some standard
10kΩ thermistors with similar characteristics are listed
in Table 2. When used with one of these thermistors
and the recommended series resistor, the MAX6682
provides output data scaled in °C over the +10°C to
+40°C temperature range.
Choose R
thermistor:
1) Decide on the temperature range of interest (for
2) Find the thermistor values at the limits of the tem-
Thermistor-to-Digital Converter
Figure 3. Thermistor Nonlinearity vs. Temperature for a Standard
Thermistor from +10°C to +40°C
Figure 4. SO Output
6
Bit
example 0°C to +70°C).
perature range. R
value (at the maximum temperature) and R
the maximum thermistor value (at the minimum tem-
perature). Also find R
_______________________________________________________________________________________
(Sign)
MSB
10
EXT
-0.05
-0.10
-0.15
-0.20
-0.25
0.25
0.20
0.15
0.10
0.05
10-BIT TEMPERATURE READING
EXT
0
9
to minimize nonlinearity errors from the
0
Choosing the External Resistor
does not cause the voltage reference
5
8
THERMISTOR NONLINEARITY
10
7
vs. TEMPERATURE
MIN
TEMPERATURE (°C)
15
MID
6
20
is the minimum thermistor
, the thermistor resistance
5
25
30
4
35
3
40
2
45
1
MAX
LSB
0
is
3) Find R
Table 3 shows nominal output data for several tempera-
tures when R
equation above for a temperature range of 0°C to
+70°C. The output data is not conveniently scaled to
the actual temperature over this range, but the linearity
is better than 2.4°C over the 0°C to +70°C range
(Figure 2). The temperature weighting over this range is
0.14925°C/LSB.
The Typical Application Circuit shows the MAX6682
interfaced with a microcontroller. In this example, the
MAX6682 processes the reading from R
mits the data through an SPI-compatible interface.
Force CS low and apply a clock signal at SCK to read
the results at SO. Forcing CS low immediately stops
any conversion in process. Initiate a new conversion by
forcing CS high.
Force CS low to output the first bit on the SO pin. A
complete read requires 11 clock cycles. Read the 11
output bits on the rising edge of the clock, if the first bit
D10 is the sign bit. Bits D10–D0 contain the converted
temperature in the order of MSB to LSB.
After the 11th clock cycle, SO goes to a high-imped-
ance state. SO remains high impedance until CS is
pulsed high and brought back low. Figure 4 is the SO
output.
The MAX6682 accuracy is relatively unaffected by
power-supply coupled noise. In most applications,
bypass V
bypass capacitor close to the supply pin of the
devices.
Self-heating degrades the temperature measurement
accuracy of thermistors. The amount of self-heating
depends on the power dissipated in the thermistor and
the dissipation constant of the thermistor. Dissipation
constants depend on the thermistor’s package and can
vary considerably.
A typical thermistor might have a dissipation constant
equal to 1mW/°C. For every mW the thermistor dissi-
pates, its temperature rises by 1°C. For example, con-
in the middle of the temperature range (+35°C for
the 0°C to +70°C range).
R
EXT
EXT
CC
=
R
EXT
using the equation below:
to GND by placing a 0.1µF ceramic
MID
Power-Supply Considerations
has been chosen according to the
(
R
R
MIN
MIN
Thermal Considerations
+
+
R
R
MAX
MAX
)
−
−
2
2
R
Serial Interface
R
MID
MIN MAX
R
EXT
and trans-