LP8863-Q1: About DITHER_SELECT

Koji Hayashi92

Mastermind 6970 points

Part Number: LP8863-Q1

Hi TI-team

I don't understand about Dither, so I have included a diagram.

(The same 1.2kHz LED PWM as in the datasheet.)

I am aware that 010b is 2 out of 8 pulses.

Therefore, 110b is 6 out of 8 pulses, as shown in the figure below.

Is this correct?

One cycle of 20MHz is 50ns, so selecting Dither will increase the On time by 50ns.

Is this understanding correct?

Best Regards,

Koji Hayashi

over 3 years ago

0 Charles-Chen over 3 years ago

TI__Genius 11836 points

Hi Koji-san，

The second question is not correct. Different dither bit will achieve different on time resolution and it is not fixed.

0 Charles-Chen over 3 years ago

TI__Genius 11836 points

Hi Koji-san，

The second question is not correct. Different dither bit will achieve different on time resolution and it is not fixed.

0 Charles-Chen over 3 years ago in reply to Charles-Chen

TI__Genius 11836 points

Hi Koji-san,

If you don't have any more questions, please help close the thread. The similar with other threads, thanks a lot.

0 Koji Hayashi92 over 3 years ago in reply to Charles-Chen

Mastermind 6970 points

Hi Charles-san

Sorry for the late reply.

So, what kind of Dither do you get with 110b?

0 Charles-Chen over 3 years ago in reply to Koji Hayashi92

TI__Genius 11836 points

Hi Koji-san,

3 bit dither with fraction of 3/4.

0 Charles-Chen over 3 years ago in reply to Charles-Chen

TI__Genius 11836 points

Hi Koji-san,

Do you have any more questions? Please help close the thread.

0 Koji Hayashi92 over 3 years ago in reply to Charles-Chen

Mastermind 6970 points

I was mistaken.

The waveform diagram for 110b is correct, right?

You answered that the second question "One cycle of 20MHz is 50ns, so selecting Dither will increase the On time by 50ns." is wrong, please explain "Different dither bit will achieve different on time resolution and it is not fixed." in detail.

0 Charles-Chen over 3 years ago in reply to Koji Hayashi92

TI__Genius 11836 points

Hi Koji-san,

For example, when the 1-bit dither is selected, the width of every second PWM pulse is increased by one LSB (one 20-MHz

clock period). And the average pulse width is 1/2 of LSB (one 20-MHz clock period). I suggest to first read through the datasheet carefully and then you will have a better understanding for the mechanism of dither.

Power management

Power management forum

LP8863-Q1: About DITHER_SELECT