Datasheet

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Soft Start
5V
VCOMP
VCOMP
FAULT
gmv
I
SS
= -30uA
for VSENSE < 4.75V
during Soft-Start
+
VSENSE
System Protection
Feedback
Voltage
OVP 105% V
REF
OLP
Soft-Start
(No EDR)
OLP
OVP
(No Gate Output)
Run
UVD
(EDR on)
Protection
State
100% V
REF
OLP/SS 16% V
REF
Run
EDR 95% V
REF
UCC28019
SLUS755B – APRIL 2007 – REVISED DECEMBER 2007
VCOMP, the output of the voltage loop transconductance amplifier, is pulled low during UVLO, IBOP, and
OLP(Open-Loop Protection)/STANDBY. After the fault condition is released, soft start controls the rate of rise of
VCOMP in order to obtain a linear control of the increasing duty cycle as a function of time. During soft start a
constant 30 µ A of current is sourced into the compensation components causing the voltage on this pin to ramp
linearly until the output voltage reaches 85% of its final value. At this point, the sourcing current begins to
decrease until the output voltage reaches 95% of its final rated voltage. The soft-start time is controlled by the
voltage error amplifier compensation components selected, and is user-programmable based on desired loop
crossover frequency. Once V
OUT
exceeds 95% of rate voltage, EDR is no longer inhibited.
Figure 20. Soft Start
System level protection features keep the system in safe operating limits:
Figure 21. Output Protection States
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Product Folder Link(s): UCC28019