TSC2007-Q1
SBAS545 –SEPTEMBER 2011
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INTERNAL TEMPERATURE SENSOR
In some applications, such as battery recharging, an ambient temperature measurement is required. The
temperature measurement technique used in the TSC2007-Q1 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 TSC2007-Q1 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 10μA 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 = 732μV with VREF = 3.0V).
VDD
+IN
Converter
-IN
GND
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:
kT
q
DV +
@ ln(N)
(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 = the 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:
q @ DV
k @ ln(N)
T +
(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.
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