TSC2102 datasheet(19/54 Pages) TI

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TSC2102

SLAS379A− APRIL 2003 − REVISED JUNE 2004

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Temperature Measurement

In some applications, such as battery recharging, a measurement of ambient temperature is required. The temperature

measurement technique used in the TSC2102 relies on the characteristics of a semiconductor junction operating at a fixed

current level. The forward diode voltage (VBE) has a well-defined characteristic versus temperature. The ambient

temperature can be predicted in applications by knowing the 25

°C value of the VBE voltage and then monitoring the delta

of that voltage as the temperature changes.

The TSC2102 offers two modes of temperature measurement. The first mode requires a single reading to predict the

ambient temperature. A diode, as shown in Figure 14, is used during this measurement cycle. This voltage is typically 600

mV at 25

°C with a 20-µA current through it. The absolute value of this diode voltage can vary a few millivolts. During the

final test of the end product, the diode voltage must be stored at a known temperature. Further calibration can be done to

calculate the precise temperature coefficient of the particular device. This method has a temperature resolution of

approximately 0.3

°C/LSB and accuracy of approximately 1°C.

A/D

Converter

MUX

X+

Temperature Select

TEMP0 TEMP1

Figure 14. Functional Block Diagram of Temperature Measurement Mode

The second mode uses a two-measurement (differential) method. This mode requires a second conversion with a current

82 times larger. The voltage difference between the first (TEMP1) and second (TEMP2) conversion, using 82 times the

bias current, is represented by:

ln(N)

where:

N is the current ratio = 82

k = Boltzmann’s constant (1.38054

• 10−23 electrons volts/degrees Kelvin)

q = the electron charge (1.602189

• 10−19 °C)

T = the temperature in degrees Kelvin

This method provides resolution of approximately 1.5

°C/LSB and accuracy of approximately 1°C. The equation for the

relation between differential code and temperature may vary slightly from device to device and can be calibrated at final

system test by the user.

TSC2102 Datasheet(PDF) 19 Page - Texas Instruments