Datasheet

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INTERNAL TEMPERATURE SENSOR
Converter
AGND
SNSVDD
TEMP1 TEMP2
+IN
-IN
DV +
kT
q
@ ln(N)
(3)
T +
q @ DV
k @ ln(N)
(4)
TSC2004
SBAS408E – JUNE 2007 – REVISED MARCH 2008
In some applications, such as battery recharging, an ambient temperature measurement is required. The
temperature measurement technique used in the TSC2004 relies on the characteristics of a semiconductor
junction operating at a fixed current level. The forward diode voltage (V
BE
) has a well-defined characteristic
versus temperature. The ambient temperature can be predicted in applications by knowing the +25 ° C value of
the V
BE
voltage and then monitoring the delta of that voltage as the temperature changes.
The TSC2004 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 27 , is used during this measurement cycle. This voltage is typically 580mV at +25 ° C with a 10 µ A current.
The absolute value of this diode voltage can vary by a few millivolts; the temperature coefficient (T
C
) of this
voltage is very consistent at – 2.1mV/ ° C. During the final test of the end product, the diode voltage is stored at a
known room temperature, in system memory, for calibration purposes by the user. The result is an equivalent
temperature measurement resolution of 0.3 ° C/LSB (1LSB = 610 µ V with V
REF
= 2.5V).
Figure 27. 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:
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 much improved absolute temperature measurement, but a lower resolution of
1.6 ° C/LSB. The resulting equation to solve for T is:
Where:
Δ V = V
BE
(TEMP2) – V
BE
(TEMP1) (in mV).
∴ T = 2.573 ⋅ Δ V (in K),
or T = 2.573 ⋅ Δ V – 273 (in ° C).
Temperature 1 and/or temperature 2 measurements have the same timing as Figure 46 .
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