
TLV320AIC26
SLAS412 DECEMBER 2003
www.ti.com
30
Temperature Measurement
In some applications, such as battery recharging, a measurement of ambient temperature is required. The temperature
measurement technique used in the ’AIC26 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 ’AIC26 offers two modes of temperature measurement. The first mode requires a single reading to predict the ambient
temperature. A diode, as shown in Figure 25, is used during this measurement cycle. This voltage is typically 600 mV at
25
°C with a 20-A 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 6°C.
TEMP0 TEMP1
MUX
A/D
Converter
Temperature Select
X+
Figure 25. 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:
kT
q
ln(N)
where:
N is the current ratio = 82
k = Boltzmann’s constant (1.38054
1023 electrons volts/degrees Kelvin)
q = the electron charge (1.602189
1019 °C)
T = the temperature in degrees Kelvin
This method provides resolution of approximately 1.5
°C/LSB and accuracy of approximately 5°C. The temperature
measured by the ’AIC26 is an approximate number with an accuracy of 5
°C to 6°C depending on the method used. Further,
it has been found that the measurement varies significantly from device to device. Therefore, it is recommended that the
user calibrate the temperature measurement during final system test.