P r o d u c t I n n o v a t i o n F r o m
PA119CE • PA119CEA
THERMAL SHUTDOWN
STABILITY
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.
Thermalprotectionisafairlyslow-actingcircuitandtherefore
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.
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
thevaluesgiveninthetableunderexternalconnectionsand
interpolateifnecessary.Thephasemargincanbeincreased
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.
International customers can also request support by contacting their local Cirrus Logic Sales Representative.
To find the one nearest to you, go to www.cirrus.com
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PA119U
5
CIRRUS [ CIRRUS LOGIC ]
