LP8863-Q1: LED PWM ON TIME

Koji Hayashi92

Mastermind 7030 points

Part Number: LP8863-Q1

Hi TI-team

My customer want to know ON time.

At hybrid dimming, the LED PWM turns on and off at 12.5% or less.

In this situation, the ON time indicates which of the following times?

Best Regards,

Koji Hayashi

over 4 years ago

0 Charles-Chen over 4 years ago

TI__Genius 11836 points

When the brightness code is below 12.5% of the full scale.

0 Koji Hayashi92 over 4 years ago in reply to Charles-Chen

Mastermind 7030 points

Could you be more specific?

For example, when the LED PWM frequency is 152Hz, 0001h is 803ns.

1/152*1/8192(2000h)=803ns

Which period of time does 803ns correspond to, red, blue, or green in the above diagram?

0 Charles-Chen over 4 years ago in reply to Koji Hayashi92

TI__Genius 11836 points

Hi Koji-san,

I am confused about your figure. For details, please refer to figure 18 of the brightness code with hybrid dimming mode in the datasheet of LP8863-Q1. It may be helpful to you.

0 Koji Hayashi92 over 4 years ago in reply to Charles-Chen

Mastermind 7030 points

It is my understanding that below 2000h, the LED PWM Duty changes to adjust the current value.

The Peak current at that time will be 12.5%, for example, when 100mA is set, the peak current will be 12.5mA.

At 50%, the ON time is 1000h, which is 3.29ms, half of the 6.59ms at 1/152Hz.

Which time in the figure below is correct to represent 3.29ms?

Am I right in thinking that it is blue?

0 Koji Hayashi92 over 4 years ago in reply to Koji Hayashi92

Mastermind 7030 points

How is the situation ?

+1 Charles-Chen over 4 years ago in reply to Koji Hayashi92

TI__Genius 11836 points

Hi Koji-san,

Actually, your description is right. For the output pwm pulse, I think both three figures are not right. You can image that the ideal output is 3.29ms square waveform and for the rising edge and falling edge. Both edges have some delay. But the average time is around 3.29ms if the rising time and falling time are almost same.

0 Koji Hayashi92 over 4 years ago in reply to Charles-Chen

Mastermind 7030 points

HI Charles-san

Thank you for response.

I will tell my customers to measure the on-time at 1/2 of the peak current.

Best Regards,

Koji Hayashi

Power management

Power management forum

LP8863-Q1: LED PWM ON TIME