LP8863-Q1: LP8863 - flickering led

Hi Zeev,

Zhiqian is out of office and will reply to your questions when he is coming back.

BTW, could you please upload if you have some waveforms captured as well? Thanks

BR

Patrick

Hi,

I read the status register and see the followed fault:

Boost OVP High Status

Boost OVP Low Status

The Boost OVP High Status is not exist in the LP8863-Q1_Design Tool and the Boost OVP Low Status have legal value.

The values is depended on the FB resistor.

pls. advise which value to put.

regards

zeev gerber

Hi Zeev,

I have noticed our expert and he will reply to you later.

BR

Patrick

Hi,

I change the top feedback resistor from 432K to 562K.

Boost OVP High Status is now O.K

Boost OVP Low Status is now O.K

but

Boost Over-current now fail.

Pls. advise

regards

zeev gerber

Hi,

I change the top feedback resistor to 510K.

now it's working with out fault.

pls. explain the tolerance allowed of the feedback on the led driver.

the LP8863 design tools is not working wall in this calculation (all values are O.K)

without understanding of the issue I couldn't use this component in my system.

regards

zeev gerber

Hi, Zeev

Could you pls kindly share the output LED setup/LED forward voltage and LED output current first?

I can help to check if anything is wrong.

Hi,

In my first mail I attached the card schematic and the LP8863 design tools with the values I used.

The flickering exist in all output LED setup and LED output current.

Hi, Zeev

I want to double confirm that, Vout will be lower than Vin? If so, device will meet some problem.

Hi,

Vin is 24V.

There are 35 led in configuration of 5X7.

5 led in a row need less than 24V, but as I understand the led voltage is adaptive.

no warning about the Vout < Vin in LP8863 data sheet or in LP8863 design tools

pls. advise next steps

zeev gerber

Hi Zeev

It is the basic background. Boost output cannot be lower than VIN. Could you change the string number？

Hi,

I change Rfb1 to 510K and it's working without flickering.

The question is why Boost Over-current fail when Rfb1 is 560K?

what are the tolerance of the devise?

I lost all the confidence from the devise and from the Design Tool and DS of the LP8863

Zeev Gerber

Hi,

I change Rfb1 to 510K and it's working without flickering.

The question is why Boost Over-current fail when Rfb1 is 560K? (I try twice)

Zeev Gerber

Hi,

currently Vout = Vin.

It's only issue of power consumption on the devise.

The question is why Boost Over-current fail when Rfb1 is 560K (RFB2 = 100K)?

Zeev Gerber

Hi Zeev,

Our expert will reply to you later, thanks for your patience.

BR

Patrick

Hi, Zeev

We don't recommend use boost topology when Vout is lower than Vin. If you want to use it pls consider SEPIC model.

Very disappointing

Hi, Zeev

It is the limit of boost topology, pls kindly consider the SEPIC topology as the solution.