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BD7690FJ-E2

Power Factor Correction Controller IC

ROHM Semiconductor 

BD7690FJ

(3) About ErrAMP

(3-1) gmAMP

The VS pin monitors a divided voltage of the output voltage. The ripple voltage of AC frequency (50Hz/60Hz) overlaps with VS

pin. gmAMP removes this ripple voltage. gmAMP compares VAMP (2.5V typ.) with the divided voltage of the output voltage,

gmAMP controls the EO voltage by this gap. When EO pin voltage rises, ON width of the OUT pin becomes wide. When the EO

voltage less than about 0.7V, the IC stops switching. Therefore it can stop switching operation when EO pin connects to the

GND.

External parts value of EO pin should be set that the ripple voltage of AC frequency does not conduct to EO pin. And, please

confirm it by real board.

PFC Output

VS

-

+

2.50V

EO_ VSEO

Figure 6. gmAMP block diagram

(3-2) VS short protection

VS pin has a short protection function.

A state of PFC output voltage < VSHORT (0.3V typ.) continues more than TVS_SH (150us typ.), it stops switching.

It shows operation in Figure 7.

PFC

output Vout

VS

V SHORT

OUT

T VS_SH

Switching stop

Figure 7. Operation of VS short protection

(3-3) VS low voltage gain increase function

When output voltage decreases by output load sudden changes, an output voltage drop period becomes long because a voltage

control loop is slow. VS pin voltage becomes lower than VGUP (2.25V typ.) (equivalent to -10% of output voltage), the error

amplifier increases a gain. By this operation, ON width of OUT increases and prevents a long-term drop of the output voltage.

When VS pin voltage rises from VGUP(2.25V typ.), this operation stops.

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27. Mar. 2017 Rev.002

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