FSD200B Просмотр технического описания (PDF) - Fairchild Semiconductor

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FSD200B

Green Mode Fairchild Power Switch (FPS™)

Fairchild Semiconductor 

FSD210B, FSD200B

6. Burst operation : In order to minimize the power dissi-

pation in standby mode, the FSD200B/210B enter burst

mode operation. As the load decreases, the feedback voltage

decreases. The device automatically enters burst mode when

the feedback voltage drops below VBURL(0.58V). At this

point switching stops and the output voltages start to drop.

This causes the feedback voltage to rise. Once is passes

VBURH(0.64V) switching starts again. The feedback voltage

falls and the process repeats. Burst mode operation alter-

nately enables and disables switching of the power MOSFET

to reduce the switching loss in the standby mode.

Vo

Voset

fs=1/ts

138kHz

134kHz

130kHz

Drain

Current

ts

4ms

t

Figure 13. Frequency Modulation Waveform

VFB

0.64V

0.58V

Ids

CISPR22Q(PK)

CISPR22A(AV)

Vds

t

5uA

4

Vfb

OSC

250uA

S

Q

R

GATE

DRIVER

on/off

0.64V

/0.58V

FSD2xxB

Burst Operation Block

Figure 12. Burst Operation Function

Frequency(MHz)

Figure 14. FSDH0165 Full Range EMI scan(100kHz, no

Frequency Modulation) with charger set

CISPR22Q(PK)

CISPR22A(AV)

7. Frequency Modulation : Modulating the switching fre-

quency of a switched power supply can reduce EMI by

spreading the energy over a wider frequency range than the

bandwidth measured by the EMI test equipment. The

amount of EMI reduction is directly related to the depth of

the reference frequency. As can be seen in Figure 13, the fre-

quency changes from 130KHz to 138KHz in 4ms for the

FSD200B/210B. 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.

Frequency(MHz)

Figure 15. FSD210B Full Range EMI scan(134kHz, with

Frequency Modulation) with charger set

11

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