DS90UB948-Q1: After setting the gpio2 output pwm to the backlight chip, the 20v output of the backlight chip (LP8864SQRHBRQ1) disappears, the backlight flashes momentarily, and then the problem is not bright

Set the backlight driver IC (TI-LP8864SQRHBRQ1) register, change the Brightness to be controlled by the chip itself, you will see the back light, and soon the output of 20V power is no longer, the phenomenon is the same as the external pwm control.

Specific register Settings are as follows:

0x05 register, bit 9-8, value; 2h = Brightness controlled by DISPLAY_BRT register

0x01 register: value 0x7F

0x00 register: value 0xFF

Hi, Lu

Could you pls kindly share what is the required Vf for LED string?

Also, could you pls read below register to see which fault is reported for the device.

Hi Wu,

I'm not sure the required Vf for LED string, but the value of AUTO_LED_STRING_CFG is 0[4 separate strings], our hardware said its okay.

And the value of LP8864SQRHBRQ1 registers shown as below:

Before external pwm input:

After external pwm input:

Please help to check.

Thanks.

硬件对此处做了相关修改尝试，但仍然不行

HI, Lu

depending on your register setup, 0x14 register is changed from 0x10 to 0x13, it means that device is meet ALL_LED_FAULT. pls let hardware to check the connection, also it is better to share the waveform for below point:

SW/OUT/Boost output FB to see what happened for the device.

Hi Wu,

Sorry for mistake information.

Today, our hardware colleague took your advice and changed the boost max value, it works.

So, the problem has been resolved.

Thanks.