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OPA378

Output

R

SHUNT

Load

V+

V+

R

G

R

L

R

(2)

1

10kW

R

BIAS

+5V

zener

(1)

Twozener

biasingmethods

areshown.

(3)

MOSFETratedto

stand-offsupplyvoltage

suchasBSS84for

upto50V.

(1)zenerratedforopampsupplycapability(thatis,5.1VforOPA378).

(2)Current-limitingresistor.

(3)ChoosezenerbiasingresistorordualNMOSFETs(FDG6301N,NTJD4001N,orSi1034)

NOTES:

R

SHUNT

C

BYPASS

OPA378

3V

1MW

60kW

100kW

1MW

NTC

Thermistor

V

1

-In

V

2

+In

R

1

R

2

2

3

5

6

1

R

2

OPA378

OPA378

INA152

V

O

V =(1+2R /R

O

2

1

2

1

)(V

V )

-

OPA378

OPA2378

SBOS417 – JANUARY 2008

Figure 27 shows a high side current monitor. The

small power supply window of voltage. For the

5.5V.Two possible methods are shown to bias the

connected to the noninverting input of the op amp.

zener, the customary resistor bias and a current

The op amp feedback forces a replica of this voltage

mirror. To operate over at the lowest possible voltage

for the shunt supply, current mirror biasing could also

be used. In either case, note that the voltage at the

to provide whatever current is most convenient to the

output terminal of this circuit is restricted by whatever

designer based on this voltage drop. The MOSFET

conveys this current out of its drain to ground, where

diode on the noninverting input provide protection in

situations where the load might be shorted out. These

components clamp the noninverting input to within a

diode drop of the negative rail of the op amp under

amp is powered by the zener diode, which forms a

short-circuit conditions.

Figure 27. High-Side Current Monitor

Figure 28. Thermistor Measurement

Figure 29. Precision Instrumentation Amplifier

Copyright © 2008, Texas Instruments Incorporated

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