Use of 1/3 Bias with a STM32L073V8T6 : VLCD1 and VLCD2 are not at 1/3VLCD and 2/3VLCD

[Alexandre_B]

Hello,

I am working on a STM32L073V8T6. I want to use the 1/3 bias functionnality to manage a screen.

I have configured the contrast control to 3.26V, the Mode to 1/4 Duty Cycle and the Bias Selector to 1/3 Bias.

But if I write something to COM0 and I look at the signal with the scope, I get 4 levels :

0V -- 1.3V -- 2.0V and 3.3V instead of :

0V -- 1.1V -- 2.2V and 3.3V.

I have already added 150nF external capacitors on and configured the resistors with the software to have low resistors.

Why do I have 1.3V and 2.0 instead of 1.1V and 2.2V ? Is there something that I have forgotten ?

Also, I couldn't find the RL and RH values in the datasheet. Is it possible to have it, plase ?
Thank you,
Alexandre

[waclawek.jan]

Is this under load?

Have you tried High drive?

JW

[Alexandre_B]

Thank you for your answer.

I have tried it both loaded and unloaded. The results are the same.

I also tried with High Drive, but it made no difference.

Thank you for the screenshot of RL and RH.

Regards,
Alexandre