TMP35/TMP36/TMP37

Rev. F | Page 8 of 20

FUNCTIONAL DESCRIPTION

An equivalent circuit for the TMP3x family of 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

by the following relationship:

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

×

=

Δ

E,Q2

E,Q1

T

BE

A

A

V

V

ln

Resistors R1 and R2 are used to scale this result to produce

the output voltage transfer characteristic of each temperature

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

3X

25µA

2X

Q2

1X

R1

R2

R3

7.5µA

Q3

2X

GND

Q4

Q1

10X

6X

Figure 22. Temperature Sensor Simplified Equivalent Circuit

Table 4. TMP3x Output Characteristics

Sensor

Offset

Voltage (V)

Output Voltage

Scaling (mV/°C)

Output Voltage

@ 25°C (mV)

TMP35

0

10

250

TMP36

0.5

10

750

TMP37

0

20

500