Current limit resistor value can be calculated as follows:

Rcl=3/Ilim

It is recommended that the user set up the value of current limit

as close as possible to the maximum expected output current

to protect the amplifier. The minumum value of current limit

resistance is 33 ohms. The maximum practical value is 500

ohms. Current limit will vary with case temperature. Refer to

the typical performance graphs as a guide. Since load current

passes through the current limit resistor, a loss in output volt-

age swing will occur. The following formula approximates out-

put voltage swing reduction:

When the device is in current limit, there will be spurious oscil-

lations present on the negative half cycle. The frequency of

the oscillation is application dependent and can not be pre-

dicted. Oscillation will cease when the device comes out of

current limit.

APPLICATION NOTES

CURRENT LIMIT

SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational ampli-

fier has two distinct limitations:

1. The current handling capability of the die metallization.

2. The temperature of the output MOSFET's.

NOTE: The output stage is protected against transient flyback.

However, for protection against sustained, high energy flyback,

external fast-recovery reverse biased diodes should be used.

The MSK 162/163 are internally compensated for closed loop

gains of 10 V/V or greater. The majority of applications the

MSK 162/163 are used in involve gains greater than 10 V/V

because the output is capable of swinging up to +/- 141V and

the maximum differential input voltage is only +/- 16V. A

large gain is necessary to make full use of the output voltage

swing capability of the amplifier when input voltages are small.

If closed loop gains of less than 10 V/V are required, refer to

the MSK 158/159 data sheets. The MSK 158/159 operational

amplifiers are identical to the MSK 162/163 except pins two

and six are compensation pins. The user can tailor op-amp

performance with the external connection of a series resistor-

capacitor snubber network. An effective method of checking

amplifier stability is to apply the worst case capacitive load to

the output of the amplifier and drive a small signal square wave

across it. If overshoot is less than 25%, the system will gen-

erally be stable.

STABILITY

*

Vr= Io Rcl

INPUT PROTECTION

Input protection curcuitry within the MSK 162/163 will clip

differential input voltages greater than 16 volts. The inputs are

also protected against common mode voltages up to the supply

rails as well as static discharge. There are 300 ohm current

limiting resistors in series with each input. These resistors may

become damaged in the event the input overload is capable of

driving currents above 1mA. If severe overload conditions are

expected, external input current limiting resistors are recom-

mended.

OUTPUT SNUBBER NETWORK

A 100 ohm resistor and a 330pF capacitor connected in se-

ries from the output of the amplifier to ground is recommended

for applications where load capacitance is less than 330pF.

For larger values of load capacitance, the output snubber net-

work may be omitted. If loop stability becomes a problem due

to excessively high load capacitance, a 100 ohm resistor may

be added between the output of the amplifier and the load. A

small tradeoff with bandwidth must be made in this configura-

tion. The graph below illustrates the effect of capacitive load.

Note that the compensation capacitor must have a voltage rat-

ing greater than the total rail to rail power supply voltage.

Rev. B 7/00

3