FSD200
9
6. Burst operation :
In order to minimize the power
dissipation in standby mode, the FSD200/210
implements burst mode.
Figure 6. Circuit for burst operation
As the load decreases, the feedback voltage
decreases. The device automatically enters burst mode
when the feedback voltage drops below 0.5V. At this
point switching stops and the output voltages start to
drop. This causes the feedback voltage to rise. Once is
passes 0.6V switching starts again. The feedback
voltage falls and the process repeats. Burst mode
operation alternately enables and disables switching of
the power MOSFET to reduce the switching loss in the
standby mode.
Figure 7. Burst mode operation
7. Frequency Modulation
0.2A
0.25A
0.3A
3mS
Iover
FSD200/210
I(A)
t
OSC
4
Vfb
S
R
Q
GATE
DRIVER
5uA
250uA
0.6V
/0.5V
on/off
FSD2xx
Burst Operation Block
V
FB
Vds
0.5V
0.6V
Ids
Vo
Vo
set
time
130kHz
131kHz
132kHz
133kHz
134kHz
135kHz
136kHz
137kHz
138kHz
2mS
A
B
C
130kHz
134kHz
138kHz
Sawtooth
waveform
Ton
Vfb
Vdrain
Idrain
A
B
C
