Datasheet

SHUTDOWN OPTIONS(see Block Diagram)
Since both the compensation and soft-start termi-
nals (Pins 9 and 8) have current source pull-ups,
either can readily accept a pull-down signal which
only hasto sink a maximum of 100
µA to turnoff the
outputs. Thisis subject to the added requirement of
discharging whatever externalcapacitance may be
attached to these pins.
Analternateapproachistheuseof theshutdowncir-
cuitry of Pin 10 which has been improved to en-
hance the available shutdown options. Activating
this circuit by applying a positive signal on Pin 10
performs two functions : the PWM latch is immedi-
ately set providing the fastest turn-off signal to the
outputs ; and a 150 µA current sink begins to dis-
chargethe external soft-start capacitor. If the shut-
down command is short, the PWM signal is termi-
nated without significant discharge of the soft-start
capacitor, thus, allowing, for example,a convenient
implementation of pulse-by-pulse current limiting.
Holding Pin 10 high for a longer duration, however,
will ultimately discharge this external capacitor, re-
cycling slow turn-on upon release.
Pin 10 should not be left floating as noise pickup
could conceivably interrupt normal operation.
Figure 5 : SG1525AError Amplifier.
PRINCIPLES OF OPERATION
SG2525A/27A-SG3525A/27A
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