PTN3460 - Backlight power sequence

[sylvain1]

Hello,

There is a delay of approximately 250 ms between the activation of the backlight via an I2C command (Backlight
control: 0x95) and the change of BKLTEN output.

You can see in the screenshot below, the delay measured between the start of the activation of the PWM and the activation of the BKLTEN output:

Despite a configuration of the different timings (T12, T2 and T4), we cannot reduce this delay.

Thanks for your help!

Sylvain

[brendonslade]

Moving to correct forum (this was under DSC)

[sylvain1]

I add a zoom on the i2C backlight activation command

Full view: backlight activation

[JozefKozon]

Hello Sylvain,

please see a reply from an application engineer I have contacted. Please answer his question.

DESCRIPTION

We don’t have programmable delay time for I2C command (Backlight control: 0x95) issued to the change of BKLTEN output.

The approximately 250 mS delay seems a bit longer, but I can do actual measurement on PTN3460 eval board to confirm it when I am in lab around early next week.

However I don’t see any issue for this 250 mS delay time in application, please ask customer what is the application concern or needs to shorten this delay? Did they see any issue in application?

With Best Regards,

Jozef

[sylvain1]

@Jozef

Thanks for your feedback/responses.

The approximately 250 mS delay seems a bit longer, but I can do actual measurement on PTN3460 eval board to confirm it when I am in lab around early next week.

Yes, I would like if you can take the test on the evaluation dev kit if possible. Thank you !

However I don’t see any issue for this 250 mS delay time in application, please ask customer what is the application concern or needs to shorten this delay? Did they see any issue in application?

In my use case, the PTN_BKLTEN output manages the power supply of my backlight controller (LP8556).

When my controller is powered, I configure it via I2C commands.

I am therefore obliged to put a delay (300ms) between activating the backlight (from the PTN) and configuring the controller and if the PWM signal "starts" before PTN_BKLTEN, this results in a blockage of our backlight power control.

I notice that the delay of about 250 ms does not exist the first time after the power ON sequence of the PTN.

[JozefKozon]

Hi Sylvain,

please see below comments from the application engineer.

DESCRITPION

Thanks for your feedback/responses.

The approximately 250 mS delay seems a bit longer, but I can do actual measurement on PTN3460 eval board to confirm it when I am in lab around early next week.

Yes, I would like if you can take the test on the evaluation dev kit if possible. Thank you !

Eric:> OK, will provide measurement data when it’s done.

However I don’t see any issue for this 250 mS delay time in application, please ask customer what is the application concern or needs to shorten this delay? Did they see any issue in application?

In my use case, the PTN_BKLTEN output manages the power supply of my backlight controller (LP8556).

When my controller is powered, I configure it via I2C commands.

Eric:> OK.

I am therefore obliged to put a delay (300ms) between activating the backlight (from the PTN) and configuring the controller and if the PWM signal "starts" before PTN_BKLTEN, this results in a blockage of our backlight power control.

Eric:> I don’t know why <PWM signal "starts" before PTN_BKLTEN> will be causing blockage of backlight power control issue, my understanding is that PWM signal and backlight power control (PTN_BKLTEN) are independent in most of LCD panel.

I notice that the delay of about 250 ms does not exist the first time after the power ON sequence of the PTN.

Eric:> Yes, it is correct. Panel power on/off sequence has pre-defined and programmable T2-T5 time to be adjusted which can be used to prevent unstable video to be seen on LCD panel in power on/off process.

And when user use I2C command to turn on/off LCD panel backlight which is doing in panel power on state, so the 250 mS should not cause an issue in application.

With Best Regards,

Jozef

[JozefKozon]

Hi Sylvain,

please see below a reply from the application engineer.

DESCRIPTION

I did measurement on PTN3460 eval board today, PTN3460 could turn on/off LCD panel backlight immediately

after receiving I2C backlight control command (Backlight control register: 0x95).

So it is the customer’s system limitation to cause the 250 mS delay on the backlight control in application.

Please see below waveforms for reference.

• PTN3460 turn on backlight immediately after receiving I2C command (Reg 0x95 = 0x00) to turn on backlight.

• PTN3460 turn off backlight immediately after receiving I2C command (Reg 0x95 = 0x01) to turn off backlight.

With Best Regards, 

Jozef