CM6901
SLS (SRC/LLC+SR) Controller with 1 FM+2 PWMs
Light Load PWMING
In Application , low gain configuration accomplished by connecting Rf4 and Rf5 in the closed loop configuration . The
gain for the PWM is determined by Rf4 and Rf5 where the gain is equal to -Rf5/Rf4. The voltage of VRset at which
the controller goes into FM and PWM simultaneously is equal to :
VRset = D_IN+ × (1+Rf4/Rf5) - (Rf4/Rf5) × 3 where 3 is the peak voltage of RTCT
Varyin Rset from VRset to VRset + 1.75 × Rf4/Rf5 will cause the duty cycle to vary from 50% to 0% while the
frequency will vary propotionally according to 1.75*Rf4/Rf5 where 1.75 is the peak-to-peak voltage of the RTCT
ramp. For proper operation, select Rf5 value so that the current through Rf5 {((D_IN+) - 1.2)/Rf5} should be less
than 5uA.
V o u t
V r e f
R f 1
R T
V F B
+
F E A O
V
T o
I
O S C
R f3
-
2 . 5 V
C T
R S E T
R f 4
V r e f
R f5
-
D _ IN -
D E A O
-
+
P W
M
D _ IN +
+
R T C T
2009/11/02 Rev1.4
Champion Microelectronic Corporation
Page 11
CHAMP [ CHAMPION MICROELECTRONIC CORP. ]
