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LP8866S-Q1: Dimming Ratio 32.000:1 using 152Hz

Ully Raihany

Intellectual 265 points

Part Number: LP8866S-Q1

Hi All

please help me to understand this completely, I just want to make sure.

The maximum dimming ratio for this LED driver is 32000:1, using 152 Hz
I want to know if my understanding is correct. (please correct me if i m wrong)

so the maximum ratio is 32000:1. Is it true that no matter what PWM frequency we choose, the maximum dimming ratio for each PWM frequency remains the same 32000?

And for this sentence "Dimming ratio 32000:1, using 152 Hz"

is this definition correct?

32000 : Maximum Brightness
1 : Minimum Brightness
Using 152 Hz Frequency : can be adjusted or dimmed at very fast rate 152 times/second

Thank youu

0 Zhiqian Wu 11 months ago

TI__Mastermind 20855 points

Hi, Ully

the dimming ratio means the minimum brightness compared with maximum brightness.

The minimum brightness(minimum on time) is 200ns, and the maximum brightness is related with the dimming frequency(equal to 1/f).

so the dimming ratio is 1/f:200ns=5000000/f So for 152Hz, the dimming ratio is 32000:1.

0 Ully Raihany 11 months ago in reply to Zhiqian Wu

Intellectual 265 points

Hi Zhiqian,

so if i choose the PWM Frequency 305Hz, the maximum ratio is not 32000?

0 Zhiqian Wu 11 months ago in reply to Ully Raihany

TI__Mastermind 20855 points

HI, Ully

correct.

0 Ully Raihany 11 months ago in reply to Zhiqian Wu

Intellectual 265 points

hi Zhiqian

okay noted,

But could you please explain it to me how to get 32000?

I tried to calculate with this 1/f:200ns=5000000/f So for 152Hz, the dimming ratio is 32000:1. but cannot find how to get 32000.

Because i would like to know all of the maximum dimming for each PWM Frequency

Thank you

+1 Zhiqian Wu 11 months ago in reply to Ully Raihany

TI__Mastermind 20855 points

Hi, Ully

I cannot understand your question, what you mean?

5000000/152=32894, which means it can reach 32000:1.

0 Ully Raihany 11 months ago in reply to Zhiqian Wu

Intellectual 265 points

Hi Zhiqian,

Sorry I missed it,
OK, I understand now, thank you

So for the other freq, for example:

305Hz: 5000000/305 =16393

correct right?

+1 Zhiqian Wu 11 months ago in reply to Ully Raihany

TI__Mastermind 20855 points

Hi, Ully

correct, If you don't have any questions, pls close this thread.