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Datasheet

BD9478F

TSZ02201-0F1F0C100010-1-2

© 2012 ROHM Co., Ltd. All rights reserved.

24. Jul.2012 Rev.002

www.rohm.com

TSZ22111

・15・001

●About Dimming Function

Burst Frequency Free Run Function

Because PLL is incorporated, Free Run operation is possible for burst frequency.

PLL circuit will operate like it synchronizes with the frequency of signal input to VSYNC pin.

Then, the voltage that is in proportion to the frequency will be generated in LPF pin.

When LPF pin voltage becomes 0.35V or lower, it will judge the external burst frequency is abnormal and clumps with the

frequency of fPLLmin. Then, PLL frequency is changed to Free Run frequency. (note1)

When the burst frequency becomes normal and LPF pin becomes over 0.9V, it will return to the state that synchronizes

with the burst frequency.(note2)

In the same way, when LPF pin becomes 2.75V or more, it will clump with the frequency of fPLLmax.

When the burst frequency becomes normal and LPF2 pin becomes 2.65V or lower, it will return to the state that

synchronizes with the burst frequency.

When LPF pin becomes 0.15V or lower, it will judge the external burst frequency is not inputted and switches to the

frequency of fPLLtyp.(Free Run mode)

Note1

If fVSYNC is less than fPLLmin, the input of VCO is fixed to 0.36V inside IC, and PWM frequency is fixed

to fPLLmin. However, since it is fVSYNC<fPLLmin, a LPF terminal approaches 0V.

Then, it is set to LPF<0.15V, and it shifts to Free Run mode and PWM frequency is set to fPLLtyp.

Note2

In order to shift to PLL mode, it is necessary to input bigger frequency than Free Run frequency into VSYNC.

Figure 13.