BD9470AFM・BD9470AEFV

PWM5

PWM6

PWM4

PWM2

PWM3

PWM1

PGND

RCS

CS

N

OVP

LED1

LED2

LED3

LED4

LED5

LED6

FB

CFB

RFB

●FB current Source mode・Sink/Source mode

The output of GMAMP is constant current control in normal operation ans output anout±100uA(typ.) in this IC.

But, when PWM scanning operation and local dimming is performed, total LED current and output voltage will different by

each timming and FB feedback voltage.The below describes the this operation.

As above shown,short PWM1,2,3 ans PWM4,5,6, assumed that scanning operation is performed.

At this time, the sequence is described as below.

①When

PWM4,5,6=High→Low, FB voltage, VOUT（OVP）voltage is copied

②Copied voltage is hold.

③When PWM1,2,3=High again, normal DCDC operation

④When PWM4,5,6=High again, LED current increase.

⑤Because LED current increase resulting in FB voltage change.it take a long transition time because FB source current is

100uA at this time, therefore FB voltage is not insufficient and output voltage and LED current will drop.

⑥FB voltage reaches the feedback voltage and LED current and output voltage will operate normally.

In other words, ILED current drops at the point ⑤, This may be due to the transition time of the behavior that FB current

sink first and then charge again.

Figure 26. Timing chart of FB sink/source mode

PWM

1,2,3

PWM

4,5,6

FB

ILED

①

④

③

⑤

②

⑥

VOUT

21/35

TSZ02201-0F10C1002000-1-2

© 2013 ROHM Co., Ltd. All rights reserved.

19.Oct.2013 Rev.003

www.rohm.com

TSZ22111・15・001