LP8863-Q1: Brightness [15:0]

Koji Hayashi92

Mastermind 6970 points

Part Number: LP8863-Q1

Hi TI-team

I have a question.

In the case where the customer inputs 0.016% in PWM input.

The result is 0.016*65536/100 = 10.48576.

This is rounded to 10, which is 10/65536*100 = 0.015258789%.

If you round up to 11, the result is still 0.016784668%.

Am I correct in saying that I cannot get 0.016%?

Also, in the circuit, does it work with rounding up or rounding off?

Best Regards,

Koji Hayashi

over 3 years ago

0 Charles-Chen over 3 years ago

TI__Genius 11836 points

Hi Koji-san,

If you want to get 0.016%, you could use direct PWM mode. In phase shift PWM mode, you need to input according to the PWM resolution(16bit) and the PWM frequency and your understanding is right. The identified PWM duty cycle can also be readback in registers through communication interface.

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

Mastermind 6970 points

Hi Charles-san

Thank you for quick response.

When the customer entered a PWM Duty of 0.016%, two different LED PWM pulse widths were produced.

The difference is approximately 800ns.

This corresponds to the ON time per bit, which is the LED PWM frequency of 152Hz divided by 8192 (2000h) at 12.5% LED current.

(1/152/8192=803ns)

What could be the cause of the two different ON times, 10 (8.03us) and 11 (8.83us)?

Is it because the duty cycle of the customer's PWM input is fluctuating slightly?

+1 Charles-Chen over 3 years ago in reply to Koji Hayashi92

TI__Genius 11836 points

Hi Koji-san,

I think PWM jitter is the main reason.

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

Mastermind 6970 points

Hi Charles-san

I understand.

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LP8863-Q1: Brightness [15:0]