MB39C601 Datasheet, PDF (13/37 Pages) Cypress Semiconductor – High power factor in single conversion

MB39C601
8.4 Power-Up Sequencing
When the voltage is input to VBULK, the electric charge is charged to capacitance of the VCG pin (CVCG) through starting resistor
(Rst). So, the voltage of the VCG pin rises. The voltage of the DRN pin rises by source follower when the voltage of the VCG pin
reaches the threshold voltage of the external HVMOSFET.
The DRN pin is connected with the VDD pin through the internal VDD Switch, and VDD capacitor (CVDD) is charged from the DRN
pin. When the voltage at the VDD pin reaches the threshold voltage of UVLO, the VDD Switch is turned off, and the internal Bias
circuit operates, and the switching is started.
After the switching begins, the voltage at the VDD pin is supplied from Auxiliary Winding through the external diode (DBIAS). The
voltage of an Auxiliary Winding is decided by rolling number ratio of Auxiliary Winding and Secondary Winding, and the voltage of
Secondary Winding. Therefore, the voltage at the VDD pin is not supplied, until the voltage of Auxiliary Winding rises more than the
voltage at the VDD pin. In this period, it is necessary to set the capacitor of the VDD pin to prevent the voltage of the VDD pin from
falling below the threshold voltage of UVLO.
The external Schottky diode (D1) is required between the DRN pin and VDD pin. This diode is used to prevent the current that
flows through the body diode of the VDD Switch.
Current Passing When Starting
CVDD
D1
DBIAS
VDD
8
VBULK
Rst
Ist
HV-MOSFET
CVCG
VDD Start-up Current
VDD Operating and LPM Current
VCG
5
Primary
Winding
Auxiliary
Winding
10V/8V
UVLO
Fault
VDD
Switch
VCG
14V
Shunt
Enable
PWM
2V
HS
Drive
Driver
PWM
Control
DRN
6
7 ^GND
Document Number: 002-08393 Rev.*A
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