LP8866S-Q1: Constant Frequency

Hi, Ully

You can set the frequency by PWM_FSET

Hi zhiqian,

Is it refer to this table: 

this is only the example,

So, if I use PWM-FSET Resistor 4.75kOhm, the LED PWM frequency will be 305Hz? 

is this LED PWM Frequency same as a constant frequency, ?

as i know, A constant frequency refers to a signal that repeats itself at a steady and unchanging rate over time, and its different with the LED PWM Frequency.

I'm still a little unsure on this part, please help to explain it to me

Thank you

Hi, Ully

You mean the oscillator of the PWM frequency? it is 20MHz.

Hi Zhiqian,

before that, I would like to confirm one thing, 

If we use the dimming mode " Hybrid Mode" will the PWM Frequency LED change every time there is a change in brightness from lower to higher?

okey got it, so if I choose the dimming mode is Hybrid mode, and set the PWM FSET 4.7Kohm, and the LED PWM frequency is 305Hz. No matter the brightness is lower or higher the frequency is still 305 Hz right?

Hi Ully,

Our expert is out of office and will reply to your questions once coming back, thanks for your patience.

BR

Patrick

Zhiqian,

I have one more question,

you said that "No matter the brightness is lower or higher the frequency is still the same (not change), only duty cycle will have change" 

I did the measurement, in the minimum and maximum brightness, the frequency is changed. since the duty cycle is changed.  

So, is that mean that the frequency will change due to duty cycle change?

Thank you

Hi, Ully

Do you use the dither function? If not the PWM frequency is related with the PWM_FSET resistor.

Yes, i know the PWM Freq related with PWM_FSET Resistor, but i would like to make sure that if i set R_PWM_FSER resitor to 4.75KOhm to get 305Hz frequency, the PWM Freq will not change no matter the brightness is lowest or highest (Based on your previous explanation). But when i measure it, the frequency is different between the lowest and highest brightness

Actually my goal is to set the constant frequency at 305Hz. but when i set the resistor R_PWM_FSET to 4.75K and the hybrid mode, the PWM frequency is not 305Hz 

Hi, Ully

The frequency will not change, pls help to check if you do the right test.

Also, pls check about below function.

Hi Zhiqian, 

Noted,

I will send you the measurement result and the test point that I measure by mail, please help me to check that the measurement way is correct or not, because i already follow the steps and double check, but the frequency is changed..

Thank you

Hi, Ully

Ok, I will give you a feedback by email.

Noted, thank you so much

Hi, Ully

You are welcome.

Hi Zhiqian,

I have sent you an email, please check it.

Thank you

Hi Zhiqian, 

Okay noted.

Thank you