Datasheet

System Protection
VCC Under-Voltage Lockout (UVLO)
UVLO
+
+
VCC
ON
10.5V
S Q
QR
C
DECOUPLE
VCC
Auxilary Supply
GND
VCC
OFF
9.5V
UVLO
UCC28019A
SLUS828B – DECEMBER 2008 – REVISED APRIL 2009 .................................................................................................................................................. www.ti.com
System-level protection features help keep the converter within safe operating limits:
During startup, Under-Voltage Lockout (UVLO) keeps the device in the off state until VCC rises above the 10.5-V
enable threshold, VCC
ON
. With a typical 1 V of hysteresis on UVLO to increase noise immunity, the device turns
off when VCC drops to the 9.5-V disable threshold, VCC
OFF
.
Figure 20. UVLO
If, during a brief ac-line dropout, the VCC voltage falls below the level necessary to bias the internal FAULT
circuitry, the UVLO condition enables a special rapid discharge circuit which continues to discharge the VCOMP
capacitors through a low impedance despite a complete lack of VCC. This helps to avoid an excessive current
surge should the ac-line return while there is still substantial voltage stored on the VCOMP capacitors. Typically,
these capacitors can be discharged to less than 1.2 V within 150 ms of loss of VCC.
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