CM6901 Datasheet, PDF (11/15 Pages) Champion Microelectronic Corp. – SLS (SRC/LLC+SR) Controller with 1 FM+2 PWMs

CM6901
SLS (SRC/LLC+SR) Controller with 1 FM+2 PWMs
Light Load PWMING
In Application , low gain configuration accomplished by connecting R_f4 and R_f5 in the closed loop configuration . The
gain for the PWM is determined by R_f4 and R_f5 where the gain is equal to -R_f5/R_f4. The voltage of VR_set at which
the controller goes into FM and PWM simultaneously is equal to :
VRset = D_IN+ × (1+R_f4/R_f5) - (R_f4/R_f5) × 3 where 3 is the peak voltage of RTCT
Varyin R_set from VR_set to VR_set + 1.75 × R_f4/R_f5 will cause the duty cycle to vary from 50% to 0% while the
frequency will vary propotionally according to 1.75*R_f4/R_f5 where 1.75 is the peak-to-peak voltage of the RTCT
ramp. For proper operation, select R_f5 value so that the current through R_f5 {((D_IN+) - 1.2)/R_f5} should be less
than 5uA.
V out
R f1
R f3
VFB
+
2 .5 V
-
FEAO
V To I
OSC
V re f
RT
CT
R f4
RSET
V re f
D _ IN +
R f5
D _ IN - ^-
DEAO
-
+
+
PW M
RT CT
2009/11/02 Rev1.4
Champion Microelectronic Corporation
Page 11