Datasheet

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Power Supply
VCC
VCC
ON
10.5V
VCC
OFF
9.5V
I
VCC
I
VCC(start)
<200µA
I
VCC(stby)
<2.9mA
I
VCC(ON)
UVLO Soft-Start UVLORun RunFault/Standby
Controller
State
PWM
State
OFF Ramp Regulated OFF Regulated OFF
Soft-
Start
Ramp
UCC28019
SLUS755B – APRIL 2007 – REVISED DECEMBER 2007
The UCC28019 operates from an external bias supply. It is recommended that the device be powered from a
regulated auxiliary supply. 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. 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 with a
minimum value of 0.1 µ F is recommended from VCC to GND with short, wide traces.
Figure 19. Device Supply States
The device bias operates in several states. During startup, VCC Under-Voltage LockOut (UVLO) sets the
minimum operational dc input voltage of the PFC controller. There are two UVLO thresholds. When the UVLO
turn-on threshold is exceeded, the controller turns ON. If VCC falls below the UVLO lower turn-off threshold, the
controller turns OFF. During UVLO, current drawn by the device is minimal. After the device turns on, Soft Start
(SS) is initiated and the output is ramped up in a controlled manner to reduce the stress on the external
components and prevents 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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Product Folder Link(s): UCC28019