FSD210, FSD200
11
standby mode.
Figure 12. Circuit for burst operation
Figure 13. Burst mode operation
7. Frequency Modulation
: EMI reduction can be accom-
plished by modulating the switching frequency of a SMPS.
Frequency modulation can reduce EMI by spreading the
energy over a wider frequency range. The amount of EMI
reduction is directly related to the level of modulation
(Fmod) and the rate of modulation. As can be seen in Figure
14, the frequency changes from 130kHz to 138kHz in 4mS
for the FSD200/FSD210. Frequency modulation allows the
use of a cost effective inductor instead of an AC input mode
choke to satisfy the requirements of world wide EMI limits.
Figure 14. Frequency Modulation Waveforms
Figure 15. FSDH0165 Full Range EMI scan(100kHz, no
Frequency Modulation) with charger set
Figure 16. FSD210 Full Range EMI scan(134kHz, with Fre-
quency Modulation) with charger set
OSC
4
Vfb
S
R
Q
GATE
DRIVER
5uA
250uA
0.64V
/0.58V
on/off
FSD2xx
Burst Operation Block
V
FB
Vds
0.58V
0.64V
Ids
Vo
Vo
set
time
138kHz
138kHz
134kHz
130kHz
8kHz
Turn-on
Turn-off
point
Internal
Oscillator
Drain to
Source
voltage
Vds
Waveform
Drain to
Source
current
Frequency(MHz)
A
m
pl
itud
e(
dB
µ
V)
CISPR22Q(PK)
CISPR22A(AV)
A
m
pli
tud
e(d
B
µ
V)
Frequency(MHz)
CISPR22Q(PK)
CISPR22A(AV)
