Datasheet
Bias Supply
VCC
VCC
(ON)
10.5V
VCC
(OFF)
9.5V
I
CC
I
CC(start)
<200µA
I
CC(stby)
<2.9mA
I
CC(ON)
UVLO Soft-Start UVLORun RunFault/Standby
Controller
State
PWM
State
OFF Ramp Regulated OFF Regulated OFF
Soft-
Start
Ramp
UCC28019A
SLUS828B – DECEMBER 2008 – REVISED APRIL 2009 ..................................................................................................................................................
www.ti.com
The UCC28019A operates from an external bias supply. It is recommended that the device be powered from a
regulated auxiliary supply.
NOTE:
This device is not intended to be used from a bootstrap bias supply. A bootstrap bias
supply is fed from the input high voltage through a resistor with sufficient capacitance
on VCC to hold up the voltage on VCC until current can be supplied from a bias
winding on the boost inductor. For that reason, the minimal hysteresis on VCC would
require an unreasonable value of hold-up capacitance.
During normal operation, when the output is regulated, current drawn by the device includes the nominal run
current plus the current supplied to the gate of the external boost switch. Decoupling of the bias supply must take
switching current into account in order to keep ripple voltage on VCC to a minimum. A ceramic capacitor of 0.1
µ F minimum value from VCC to GND with short, wide traces is recommended.
Figure 18. Device Supply States
The device bias operates in several states. During startup, VCC Under-Voltage Lock-Out (UVLO) sets the
minimum operational dc input voltage of the controller. There are two UVLO thresholds. When the UVLO turn-on
threshold is exceeded, the PFC controller turns ON. If the VCC voltage falls below the UVLO turn-off threshold,
the PFC controller turns off. During UVLO, current drawn by the device is minimal. After the device turns on, Soft
Start (SS) is initiated and the boost inductor current is ramped up in a controlled manner to reduce the stress on
the external components and avoids output voltage overshoot. During Soft Start and after the output is in
regulation, the device draws its normal run current. If any of several fault conditions is encountered or if the
device is put in Standby with an external signal, the device draws a reduced standby current.
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