P r o d u c t I n n o v a t i o n F r o m

PA240

PA240U

5

FIGURE1

OVERVOLTAGEPROTECTION

Although the PA240 can withstand differential input voltages

up to 16V, in some applications additional external protection

may be needed.Differential inputs exceeding 16V will be clipped

by the protection circuitry.However, if more than a few milliamps

of current is available from the overload source, the protection

circuitry could be destroyed. For differential sources above

16V, adding series resistance limiting input current to 1mA will

prevent damage.Alternatively, 1N4148 signal diodes connected

anti-parallel across the input pins is usually sufficient. In more

+Vs

-Vs

OUT

+Vs

-Vs

Z1

Z2

-IN

+IN

Q1

Q2

demanding applications where bias current is important, diode

connected JFETs such as 2N4416 will be required. See Q1

and Q2 in Figure 1. In either case the differential input voltage

will be clamped to 0.7V. This is sufficient overdrive to produce

the maximum power bandwidth.

In the case of inverting circuits where the +IN pin is grounded,

the diodes mentioned above will also afford protection from

excessive common mode voltage. In the case of non-invert-

ing circuits, clamp diodes from each input to each supply will

provide protection. Note that these diodes will have substantial

reverse bias voltage under normal operation and diode leak-

age will produce errors.

Some applications will also need over-voltage protection

devices connected to the power supply rails. Unidirectional

zener diode transient suppressors are recommended. The

zeners clamp transients to voltages within the power supply

rating and also clamp power supply reversals to ground.

Whether the zeners are used or not the system power supply

should be evaluated for transient performance including power-

on overshoot and power-off polarity reversals as well as line

regulation. See Z1 and Z2 in Figure 1.

APPLICATIONREFERENCES:

For additional technical information please refer to the fol-

lowing Application Notes:

AN01: General Operating Considerations

AN03: Bridge Circuit Drives

AN25: Driving Capacitive Loads

AN38: Loop Stability with Reactive Loads

ContACting CiRRUs LogiC sUPPoRt

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