Datasheet

TMP35/TMP36/TMP37 Data Sheet
FUNCTIONAL DESCRIPTION
An equivalent circuit for the TMP35/TMP36/TMP37 micropower,
centigrade temperature sensors is shown in Figure 22. The core
of the temperature sensor is a band gap core that comprises
transistors Q1 and Q2, biased by Q3 to approximately 8 µA. The
band gap core operates both Q1 and Q2 at the same collector
current level; however, because the emitter area of Q1 is 10
times that of Q2, the V
BE
of Q1 and the V
BE
of Q2 are not equal
by the following relationship:








×=∆
E,Q2
E,Q1
T
BE
A
A
VV ln
Resistors R1 and R2 are used to scale this result to produce
the output voltage transfer characteristic of each temperature
sensor and, simultaneously, R2 and R3 are used to scale the V
BE
of
Q1 as an offset term in V
OUT
. Table 4 summarizes the differences
in the output characteristics of the three temperature sensors.
The output voltage of the temperature sensor is available at the
emitter of Q4, which buffers the band gap core and provides
load current drive. The current gain of Q4, working with the
available base current drive from the previous stage, sets the
short-circuit current limit of these devices to 250 µA.
SHUTDOWN
V
OUT
+V
S
3X
25µA
2X
Q2
1X
R1
R2
R3
7.5µA
Q3
2X
GND
Q4
Q1
10X
6X
00337-006
Figure 22. Temperature Sensor Simplified Equivalent Circuit
Table 4. TMP35/TMP36/TMP37 Output Characteristics
Sensor
Offset
Voltage (V)
Output Voltage
Scaling (mV/°C)
Output Voltage
at 25°C (mV)
TMP35 0 10 250
TMP36 0.5 10 750
TMP37 0 20 500
Rev. H | Page 8 of 19
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