TMDS181: HPD signal internal connection

Shifali N

Part Number: TMDS181

Hi,

I am using TMDS181RGZT in my design. I would like to know what is connected internally between HPD_SRC(Pin 4) and HPD_SNK(Pin 33). Is it a diode or a buffer.

Also I have attached HPD circuit that I have implemented in my board. The design is same as the 5V HPD implementation that is given in Figure35 of datasheet.

But I have given additional pullup resistor of 10kohm to HPD_SRC pin. I am expecting voltage of 3.3V at HPD_SRC(Pin 4) after mounting this pullup resistor. But obtained voltage is 0mV. Why is this behavior observed.

over 3 years ago

0 David (ASIC) Liu over 3 years ago

TI__Guru**** 176671 points

Hi,

The TMDS181 level shifts between the HPD_SNK and the HPD_SRC.

Why do you need the external pullup resistor? Are you seeing 3.3V on HPD_SRC if you don't have the pullup resistor?

Thanks

David

0 Shifali N over 3 years ago in reply to David (ASIC) Liu

Expert 2145 points

Hi David,

I would like to know what is present internal to the IC between HPD_SRC and HPD_SNK.

Figure.15 it shown as diode whereas in simplified schematics in Page 1 and in Functional Block diagram of page 25 it shows as buffer. Please clarify whether its a diode or buffer of level translator or something else.

0 David (ASIC) Liu over 3 years ago in reply to Shifali N

TI__Guru**** 176671 points

Hi,

It is a level shifter between the HPD_SNK and the HPD_SRC, it shifts 5V on the HPD_SNK to 3.3V on the HPD_SRC. With HPD_SRC driving, you do not need an external pullup.

So if you use the external level shifter, you should then HPD_SRC floating.

Thanks

David

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TMDS181: HPD signal internal connection