LP8860-Q1: PWM dimming range

Valeri Pruman

Prodigy 80 points

Part Number: LP8860-Q1

Hello

According to the data sheet the achievable dimming range is greater than 13000:1.

Is this range is available by using the PWM dimming only or is this is a combined dimming (including current dimming)?

Thanks

Valeri

over 8 years ago

0 Karl Wallinger over 8 years ago

TI__Genius 16410 points

Hi Valeri,

Let me move this to the LED driver forum, the experts there should be able to answer your question.

Regards,
Karl

0 Salome Ramirez Carrion over 8 years ago

TI__Intellectual 2180 points

Hi Valeri,

13000:1 dimming ratio is achievable when using only PWM dimming, no need for current or hybrid dimming. Typically the limiting factor for dimming ratio is the LED driver rise time and LED PWM period. So we can estimate dimming ratio as Tp_LEDPWM / Tr_LEDRISE. For example, with a 100Hz PWM (10ms) and a 400ns rise time (typical value for LP8860 minimum on time PWM input) the dimming ratio will be 10ms / 400ns >13000:1.

Hope this helps.

Salome

0 Valeri Pruman over 8 years ago in reply to Salome Ramirez Carrion

Prodigy 80 points

Hi
Thanks for your help - this answers my question.
The problem that somehow I can't test the PWM pin input method on the EVM. I do can play with the PWM via the I2C registers. I did exactly what user guide of the EVM says, but the PWM pin control doesn't work - the LEDs stay OFF.
May be you know what can cause this problem?
Thanks
Valeri

0 Salome Ramirez Carrion over 8 years ago in reply to Valeri Pruman

TI__Intellectual 2180 points

Please refer to the following e2e thread:

Power management

Power management forum

LP8860-Q1: PWM dimming range