MB3769A Datasheet, PDF (17/26 Pages) Fujitsu Component Limited. – SWITCHING REGULATOR CONTROLLER

MB3769A
fOSC ~
1
0.8 x CT x RT
CT ~
1x
4
0.8 x RT
4.5 - VL
(tcycle - tP ) [pF] (RT: kΩ, tcycle, tP: ns)
Make VL high for a large duty cycle for the clamp circuit. The circuits below can be used because the clamp voltage must be
much lower than 1.5 V.
Fig. 19 -Clamp Circuit
VREF
R1 (4.7 kΩ)
(1.2 V)
0.1 µF ^{R2 (1.2 kΩ)}
A
VREF
(1.2 V)
820 Ω
0.1 µF
8
3
MB3761
4
5
B
In circuit A, R1 and R2 must be determined considering the effects of tP, R, or RT.
The transistor saturation voltage must be very small (<0.15 V) for any clamp circuit, so a transistor with a very small VCE (sat)
should be used.
17