TMDS361: 1.8V shows up at power supply pin when TMDS is applied AND power not supplied.

Hi Kawai,

It sounds like the receiver terminations are enabled and voltage is being back driven into the device. I will check with the design to see if this possible.

Regards,
JMMN

Kawai,

We are looking into this issue and will get back to you as soon as possible.

Hi JMMN-san, Malik-san,

Thanks for your support. I look forward for your response.

Best Regards,
Kawai

Hi JMMN-san, Malik-san,

Could you please give us your update ?
Customer is in a hurry.

Thanks in advance.

Best Regards,
Kawai

Kawai,

The terminations on the receivers should be disabled when none of the input ports are selected. I'm asking design to determine what could be connected during power down that results in back driven voltage. Can you provide a schematic?

Regards,
JMMN

Hi JMMN,

I can send you the schematic, however, I can not post here. Could you please send me a message?

Best Regards,

Kawai

Hi Kawai,

Please accept my friend request and send the schematic directly to me.

Thanks,
JMMN

Hi Kawai,

I'm not seeing any obvious leakage path in the schematic. Is HPD low when the TMDS361 is powered off? Can the customer confirm if they can see a voltage on the TMDS lines of the inputs?

I tried duplicating this on an old EVM in the lab, but I don't see the voltage on 3.3V.

Regards,
JMMN

Hi JMMN,

Thanks for your support and sorry for my delay.

Customer observed "1.8V" on power supply pin. Were you not able to see any voltage leak on the power supply pin of TMDS361B EVM ?

We are asking customer for HPD information. What happens when HPD is not low ?

For "voltage on the TMDS lines", do you want to know if the TMDS signal is really applied to the TMD361B input ?

Best Regards,
Kawai

Hi Kawai,

I wasn't able to see any leakage voltage on the EVM in lab testing.   I am wondering if HPD is high, because it could cause the source to actively drive signals to the TMDS361B.

Regards,

JMMN

Hi JMMN,

Thanks for the information. We are checking the customer HPD configuration.

Best Regards,
Kawai

Hi JMMN-san,

Customer had HPD = High when this test. It is true that source side cannot stop TMDS signal, however, since this TMDS signal is applied to no powered TMDS361B, they observes about 2.8V or some kind of voltage at the power supply pin.

So, we have two questions.

1). Is this symptom normal and how does the voltage leak happen ?

2). Can TMDS361B be used in this situation ? Would the device may get damaged ? I believe it is not exceeding the absolute maximum rating.

Best Regards,
Kawai

Hi JMMN-san,

Could you please give us your comments for the above two questions ?

I would like to close this thread with those answers.

Best Regards,

Kawai