MV1001SC

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5.2 PWM dimming

5.2.1

PWM dimming in 100% and minimum dimming ratio regions

signal should be 1 kHz or less and 1% or more, respectively.

Figure 22 Example of PWM dimming operation

As shown in Figure 22, when a PWM signal with on-duty cycle of Don is applied to the REF pin, Io becomes an average

current Io (ave) = Don x Io (max) + (1 – Don) x Io (min). In actual use, Io (min) is very small, and the equation may be

rewritten to Io (ave) ≈ Don x Io (max).

In PWM dimming, if the first switching-on timing in the H-level period is irregular, the practical Don will also become

irregular and Io will become unstable. The effect is especially significant if Don is small. To avoid this problem, the first

switching-on timing in the H-level period of every cycle aligns with each other by detecting a change of VREF from L level

to H level and forcibly outputting an on-trigger. This function helps stabilize Io (ave), even if Don is small.

Don

1-Don

Io

Io(max)

Io(ave)≒Don×Io(max)

H：2.6V or more

L：0.15V or less

t

t

H

L

IL

Io(min)

CAT.No.1A0102-1E