L9803 datasheet(71/126 Pages) STMICROELECTRONICS

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L9803

On-Chip Peripherals

71/126

The sensor generates a voltage proportional to the absolute temperature of the die. It works

over the whole temperature range, with a minimum resolution of 1LSB/°K (5mV/°K)

(Figure 36 shows the indicative voltage output of the sensor).

Note The voltage output of the sensor is only related to the absolute temperature of the

silicon junctions. Junction temperature and ambient temperature must be related taking in

account the power dissipated by the device and the thermal resistance Rthje between the

silicon and the environment around the application board.

Figure 36.

Temperature Sensor output

The output of the sensor is not ratiometric with the voltage reference for the ADC conversion

(VCC). When calculating the ADC reading error of this signal the variation of VCC must be

accounted. Additional errors are due to the intrinsic spread of the sensor characteristic.

5.5.6

Precise Temperature Measurement

To allow a more precise measurement of the temperature a trimming procedure can be

adopted (on request).

The temperature is measured in EWS and two values are stored in four EEPROM bytes

(see memory map):

T0L,T0H: temperature of the trimming measurement (in Kelvin).

VT0L,VT0H: output value of the ADC corresponding to T0 (in number of LSBs).

The corrected measurement of the temperature in Kelvin must be accomplished in the

following way:

TEMP (in °K) = VTEMP * T0 / VT0

where VTEMP is the output code in LSB of the ADC corresponding to the measurement.

Example:

If the value stored in EEPROM are:

0C7Ch: 01h ->T0H

0C7Dh: 43h ->T0L

0C7Eh: 01h -> VT0H

0C7Fh: 5Ch -> VT0L

VTEMP

Temperature (°K)

1.0

2.5

1.3

1.6

1.9

2.2

273

323

373

423

473

223

max

min

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