LP8866-Q1: weird behavior in Vout

Hi, 

Could you pls kindly check if the thermal pad connected stably in your side?

Hi!

It's very difficult to check that. Our stencil has the appropriate holes, and it should have been solded.

Andrés

Hi, Andres

Pls resolder the device for this case and have a try again.

Hi!

Sorry for the delay. I've created a Linux script to monitor all registers in real time. Here are the three scenarios I've observed:

-When I set the PWM pin high, the boost voltage rapidly decreases until ADAPT_BOOST_DIAGNOSTICS reaches 0. I do not find a VFB_OVPL error.

-Using a custom script, I manually generate a PWM signal with a duty cycle of 90% and a frequency of 152 Hz. In this case, the boost voltage decreases slowly until ADAPT_BOOST_DIAGNOSTICS reaches 0. I do find a VFB_OVPL error.

-Using a custom script, I manually generate a PWM signal with a duty cycle of 10% and a frequency of 152 Hz. Here, the boost voltage also decreases slowly, but ADAPT_BOOST_DIAGNOSTICS stabilizes around ~750. I do find a VFB_OVPL error.

Additionally, I have RFB1 = 680kΩ and RFB2 = 68kΩ. The voltage at the FB pin is 1.3V, which, based only on this voltage divider, should be approximately 2.13V. I measured this voltage using an oscilloscope.

I do not find thermal shutdown fault.

Thanks in advance

Andrés

Hi, Andres

May I kindly know what is the output LED string voltage for your design?

And do you have a time to resolder the device?

Hi!

The spec are:

I don't have time (and tools) to resolder the device yet.

Thanks in advance

Andrés

Hi, Andres

It is better to resolder it to have a try. It is unreasonable that ADAPT_BOOST_DIAGNOSTICS is turned to 0.

One possible reason is that the GND connection is not solid.

Hi!

I've resoldered it, but there's been no change in the behavior. However, I noticed that register 0x1A (LED_CURR_DIAGNOSTICS) always reads 0xFF, even after a reset with the PWM pin held low.

Hi, 

I will check it and give you a feedback tomorrow.

Hi!

Any news? I also observed that the value in register 0x1A (LED_CURR_DIAGNOSTICS) always mirrors the value in register 0x02 (LED_CURR_CONFIG). Specifically, any modification made to register 0x02 is immediately reflected in register 0x1A.
BTW, if I disconnect the flat cable from the LCD panel, I don’t receive any error. Is this behavior expected?

Thanks

Andrés

Hi Andrés,

Our expert is currently out of office and will reply to you later. Thanks for your understanding.

Best Regards,

Steven

Hi, Andres

The 0x1A is the readback register of the current setting, so it is related current you set.

And depending on your description, the boost output is turned to minimum value and stopped. It is not an abnormal action of the device. If you disconnect with the panel, at least, it will report the LED open fault. So some electrical problem may happened in your board, pls check with below step:

• Check with the voltage of OUT pin, measure BOOST/OUT/GD/FB together. I assumed that OUT pin voltage has some issue.