SN65DSI86: Regarding GPIO4 PWM Output Behavior

Billy

Can you share your schematic? The GPIO4 should drive up to 1.8V as a PWM output.

Thanks
David

Hi David

Please find the attachment on the schematic.

Please review and let me get your advice on this.

Thanks

Billy Yun

4760.DSI86.pptx

Billy

The EN pin already has an internal pullup, you would only an external pulldown cap. The typical value for the pulldown cap is 0.22uF.

The AUXP/N need to be AC-coupled.

Please make sure the main links are AC coupled as well.

If you remove R10114, are you still the 1.2V on GPIO4?

Thanks

David

Thanks David

And yes, I still see the 1.2V on GPIO4 with removing the R10114.

Any other possibility to have the behavior?

Thanks

Billy Yun

Billy

Are you seeing on multiple DSI86 or just one? Let me try and see if I can duplicate this on the DSI86 EVM.

Thanks
David

David

I am seeing this for multiple units.

This is not expected behavior. correct?

I will check it with more units again.

let me get back to you with checking more units again.

Thanks 

Billy Yun

Hi David

I have checked it with customer and the behavior is with all the units.

And I have attached latest schematic.

Could you review and let me get your advice on this?

1. What is the purpose of the signal before and after the PWM output? 

Is this not expected signal ? or a confirmation signal from DSI?

2. Which block can make the 1.2V output from GPIO4 and possible root cause

Please review and let me get your advice on this.

Thanks and  Best Regards

Billy Yun

6708.GPIO4 PWM OUT.pptx

6507.DSI86.pptx

Billy

This is the script I am using to generate the PWM from GPIO4.

<aardvark>

<configure i2c="1" spi="1" gpio="0" tpower="1" pullups="0"/>

<i2c_bitrate khz="100"/>

======GPIO CONTROL======

<i2c_write addr="0x2D" count="1" radix="16">5F 80 </i2c_write> />

======Set Brightness Level======

<i2c_write addr="0x2D" count="2" radix="16">A3 0F 10</i2c_write> />

======Set BackLight Scale======

<i2c_write addr="0x2D" count="2" radix="16">A1 FF FF</i2c_write> />

======Set PWM_PRE_DIV======

<i2c_write addr="0x2D" count="1" radix="16">A0 01</i2c_write> />

======Enable PWM======

<i2c_write addr="0x2D" count="1" radix="16">A5 02</i2c_write> />

</aardvark>

And I am not seeing the 1.2V on the scope

Have you made other changes to the EVM, in particular the pulldown cap on the EN pin?

Thanks

David

Hi David

There is no pulldown cap on the EN pin. Is it necessary to place the pulldown cap on the EN pin?

Could you help to get the GPIO4 PWM output screen shot including before and after the PWM output such like the image which I have shared?

Thanks

Billy Yun

Billy

Please see below waveforms.

The pulldown cap on the EN is required to ensure there is a proper power up timing sequence.

Thanks

David