Converter

GND

V

DD

+IN

-IN

DV +

kT

q @ ln(N)

T +

q @ DV

k @ ln(N)

TSC2017

www.ti.com

SBAS472 – DECEMBER 2009

INTERNAL TEMPERATURE SENSOR

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

temperature measurement technique used in the TSC2017 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 TSC2017 offers two modes of temperature measurement. The first mode requires calibration at a known

temperature, but only requires a single reading to predict the ambient temperature. The TEMP1 diode, shown in

Figure 22, is used during this measurement cycle. This voltage is typically 580mV at +25°C with a 10

μA current.

The absolute value of this diode voltage can vary by a few millivolts; the temperature coefficient (TC) of this

voltage is very consistent at –2.1mV/°C. During the final test of the end product, the diode voltage would be

stored at a known room temperature, in system memory, for calibration purposes by the user. The result is an

equivalent temperature measurement resolution of 0.35°C/LSB (1LSB = 732

μV with VREF = 3.0V).

Figure 22. Functional Block Diagram of Temperature Measurement Mode

The second mode does not require a test temperature calibration, but uses a two-measurement (differential)

method to eliminate the need for absolute temperature calibration and for achieving 2°C/LSB accuracy. This

mode requires a second conversion of the voltage across the TEMP2 diode with a resistance 91 times larger

than the TEMP1 diode. The voltage difference between the first (TEMP1) and second (TEMP2) conversion is

represented by:

(3)

Where:

N = the resistance ratio = 91.

k = Boltzmann's constant = 1.3807 × 10–23 J/K (joules/kelvins).

q = the electron charge = 1.6022 × 10–19 C (coulombs).

T = temperature in kelvins (K).

This method can provide a much improved absolute temperature measurement, but a lower resolution of

1.6°C/LSB. The resulting equation to solve for T is:

(4)

Where:

ΔV = VBE (TEMP2) – VBE(TEMP1) (in mV)

\ T = 2.573 × ΔV (in K)

or T = 2.573 × ΔV – 273 (in °C)

Temperature 1 and temperature 2 measurements have the same timing as the other data acquisition cycles

shown in Figure 33 and Figure 34.

Copyright © 2009, Texas Instruments Incorporated

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