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

PA119CE • PA119CEA

PA119U

5

THERMAL SHUTDOWN

The thermal protection circuit shuts off the amplifier when

the substrate temperature exceeds approximately 150°C.This

allows the heatsink selection to be based on normal operating

conditions while protecting the amplifier against excessive

junction temperature during temporary fault conditions.

Thermal protection is a fairly slow-acting circuit and therefore

does not protect the amplifier against transient SOA violations

(areas outside of the steady state boundary). It is designed to

protect against short-term fault conditions that result in high

power dissipation within the amplifier. If the conditions that

cause thermal shutdown are not removed, the amplifier will

oscillate in and out of shutdown. This will result in high peak

power stresses, destroy signal integrity, and reduce the reli-

ability of the device.

STABILITY

Due to its large bandwidth, the PA119 is more likely to

oscillate than lower bandwidth power operational amplifiers.

To prevent oscillations a reasonable phrase margin must be

maintained by:

1. Selection of the proper phase compensation capacitor. Use

the values given in the table under external connections and

interpolate if necessary.The phase margin can be increased

by using a larger capacitor at the expense of slew rate.

Total physical length (pins of the PA119, capacitor leads

plus printed circuit traces) should be limited to a maximum

of 3.5 inches.

2. Keep the external sumpoint stray capacitance to ground

at a minimum and the sumpoint load resistance (input and

feedback resistors in parallel) below 500Ω. Larger sumpoint

load resistances can be used with increased phase com-

pensation and/or by bypassing the feedback resistor.

3. Connect the case to any AC ground potential.

ContACting CiRRUs LogiC sUPPoRt

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For inquiries via email, please contact apex.support@cirrus.com.

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