REV. E

–10–

AMP02

Overvoltage Protection

Instrumentation amplifiers invariably sit at the front end of

instrumentation systems where there is a high probability of

exposure to overloads. Voltage transients, failure of a transducer,

or removal of the amplifier power supply while the signal source is

connected may destroy or degrade the performance of an unpro-

tected device. A common technique is to place limiting resistors in

series with each input, but this adds noise. The AMP02 includes

internal protection circuitry that limits the input current to

±4 mA

for a 60 V differential overload (see Figure 5) with power off,

±2.5 mA with power on.

DIFFERENTIAL INPUT VOLTAGE

4

–100

3

1

–1

–3

–4

2

0

–2

–80

–60

–40

–20

0

20

40

60

80

100

POWER ON

POWER OFF

Figure 5. AMP02’s Input Protection Circuitry Limits Input

Current During Overvoltage Conditions

Power Supply Considerations

Achieving the rated performance of precision amplifiers in a

practical circuit requires careful attention to external influences.

For example, supply noise and changes in the nominal voltage

directly affect the input offset voltage. A PSR of 80 dB means

that a change of 100 mV on the supply (not an uncommon

value) will produce a 10

µV input offset change. Consequently,

care should be taken in choosing a power unit that has a low

output noise level, good line and load regulation, and good

temperature stability. In addition, each power supply should be

properly bypassed.