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

PA243

PA243U

5

These limitations can be seen in the SOA (see Safe Operat-

ing Area graphs). Note that each pulse capability line shows

a constant power level (unlike second breakdown limitations

where power varies with voltage stress).These lines are shown

for a case temperature of 25°C and correspond to thermal re-

sistances of 5.2°C/W for the PA243DF. Pulse stress levels for

other case temperatures can be calculated in the same manner

as DC power levels at different temperatures.The output stage

is protected against transient flyback by the parasitic diodes of

the output stage MOSFET structure. However, for protection

against sustained high energy flyback external fast-recovery

diodes must be used.

HEATSinKinG

The PA243DF package has a large exposed integrated

copper heatslug to which the monolithic amplifier is directly

attached.The solder connection of the heatslug to a minimum

of 1 square inch foil area on the printed circuit board will result

in thermal performance of 25°C/W junction to air rating of the

PA243DF. Solder connection to an area of 1 to 2 square inches

is recommended. This may be adequate heatsinking but the

large number of variables involved suggest temperature mea-

surements be made on the top of the package. Do not allow

the temperature to exceed 85°C.

FIGURE1

OVERVOLTAGE pROTECTiOn

Although the PA241 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

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.

+Vs

-Vs

OUT

+Vs

-Vs

Z1

Z2

-IN

+IN

Q1

Q2

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 sup-

ply rating and also clamp power supply reversals to ground.

Whether the zeners are used or not the system power sup-

ply 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.

AppLiCATiOn REFEREnCES:

For additional technical information please refer to the fol-

lowing Application Notes:

AN1: General Operating Considerations

AN3: Bridge Circuit Drives

AN25: Driving Capacitive Loads

AN38: Loop Stability with Reactive Loads