TMP12

REV. 0

–13–

High Current Switching

As mentioned earlier, internal dissipation due to large loads on

the TMP12 outputs will cause some temperature error due to

self-heating. External transistors buffer the load from the

TMP12 so that virtually no power is dissipated in the internal

transistors and minimal self-heating occurs. This section shows

several examples using external transistors. The simplest case

uses a single transistor on the output to invert the output signal

is shown in Figure 28. When the open-collector of the TMP12

turns “ON” and pulls the output down, the external transistor

Q1’s base will be pulled low, turning off the transistor. Another

transistor can be added to re-invert the signal as shown in Figure

29. Now, when the output of the TMP12 is pulled down, the

first transistor, Q1, turns off and its collector goes high, which

turns Q2 on, pulling its collector low. Thus, the output taken

from the collector of Q2 is identical to the output of the TMP12.

By picking a transistor that can accommodate large amounts of

current, many high power devices can be switched.

2N1711

V+

4.7k

Ω

I

C

Q1

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

TMP12

Figure 28. An External Transistor Minimizes Self-Heating

MOTOR

SWITCH

RELAY

+12V

2N1711

V+

4.7k

Ω

I

C

4.7k

Ω

TIP-110

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

+5V

TMP12

Figure 30. Darlington Transistor Can Handle Large Currents

Q1

Q2

2N1711

V+

4.7k

Ω

4.7k

Ω

2N1711

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

TMP12

I

C

Figure 29. Second Transistor Maintains Polarity of TMP12

Output

An example of a higher power transistor is a standard

Darlington configuration as shown in Figure 30. The part cho-

sen, TIP-110, can handle 2 A continuous which is more than

enough to control many high power relays. In fact the

Darlington itself can be used as the switch, similar to

MOSFETs and IGBTs.