CM6903A Datasheet, PDF (11/14 Pages) Champion Microelectronic Corp. – Low Pin Count PFC/PWM CONTROLLER COMBO

CM6903A
Low Pin Count PFC/PWM CONTROLLER COMBO
UVLO
The UVLO threshold is 13V providing 3V hysteresis.
PFCOUT and PWMOUT
Both PFCOUT and PWMOUT are CMOS drivers. They both
have adaptive anti-shoot through to reduce the switching
loss. Its pull-up is a 30ohm PMOS driver and its pull-down
is a 15ohm NMOS driver. It can source 0.5A and sink 1A if
the VCC is above 13V.
PWM Section
After 10mS digital soft start, CM6903A’s PWM is operating
as a typical current mode. It requires a secondary
feedback, typically, it is configured with CM431, and photo
couple.
Since PWM Section is different from CM6800 family, it
needs the emitter of the photo couple to connected with
DCILIMIT instead of the collector. The PWM current
information also goes into DCILIMIT. Usually, the PWM
current information requires a RC filter before goes into the
DCILIMIT.
Therefore, DCILIMIT actually is a summing node from
voltage information which is from photo couple and CM431
and current information which is from one end of PWM
sensing resistor and the signal goes through a single pole,
RC filter then enter the DCILIMIT pin.
This RC filter at DCILMIT also serves several functions:
1.) It protects IC.
2.) It provides level shift for voltage information.
3.) It filters the switching noise from current information.
The pole location of the RC filter should be greater than one
sixth of the PWM switching frequency which is 67Khz for
CM6903A and which is 134Khz for CM6903A. Since the
typical photo couple should be biased around 1mA, the
resistor of the RC filter should be around 1.5V/1mA~1.5K
ohm and we suggest R is 1K ohm. Therefore, for
CM6903A, C should be around 14nF.
The maximum input voltage of the DCILIMIT pin is 1.5V.
Component Reduction
Components associated with the VRMS and IEAO pins of a
typical PFC controller such as the CM6800 have been
eliminated. The PFC power limit and bandwidth does vary
with line voltage. Double the power can be delivered from a
220V AC line versus a 110V AC line. Since this is a
combination PFC/PWM, the power to the load is limited by
the PWM stage.
2005/01/20
Champion Microelectronic Corporation
Page 11