adc128d818cimtx National Semiconductor Corporation, adc128d818cimtx Datasheet - Page 25

• Manufacturer Part Number: adc128d818cimtx
• Description: 12-bit, 8-channel, Adc System Monitor With Temperature Sensor, Internal/external Reference, And I2c Interface
• Manufacturer: National Semiconductor Corporation

15.11.3 Temperature Sensors
An external temperature sensor can be connected to any of
ADC128D818's eight single-ended input for additional tem-
perature sensing. One such temperature sensor can be
National's LM94022, a precision analog temperature sensor
with selectable gains. The application diagram shows
LM94022's gains (GS1 and GS0) both grounded indicating
the lowest gain setting. Four possible gains can be set using
these GS1 and GS0 pins.
According to the LM94022 datasheet, the voltage-to-temper-
ature output plot can be determined using the method of linear
approximation as follows:
V - V1 = (V2 - V1) / (T2 - T1) x (T - T1)
FIGURE 17. Temperature Sensor Applications
25
Where V is in mV, T is in °C, V1 and T1 are the coordinates
of the lowest temperature, and T2 and V2 are the coordinates
of the highest temperature.
For example, to determine the equation of a line over a tem-
perature range of 20°C to 50°C, first find V1 and V2 relative
to those temperatures, then use the above equation to find
the transfer function.
For more information and explanation of this example, refer
to the LM94022 datasheet.
V - 925 mV = (760 mV - 925 mV) / (50C - 20°C) x (T - 20°C)
V = (-5.50 mV /°C) x T + 1035 mV
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