SN65DP141: No output signal

Heiko Strohmeier

Part Number: SN65DP141
Other Parts Discussed in Thread: TS3DV642,

Hello everyone,

I have a problem with my design. I set up a board with the schematics below which is part of a signal splitter. The input signals come from a cable and the output is going to TS3DV642 (mux).

For every supply pin there is a dedicated cap and there is also a plane capacitor (3x3cm) for the supply voltage. The board layout should be fine and there are two SN65DP141 on the board which behave the same. So ESD death or soldering connection problems are unlikely. I checked supply voltages and also did a measurement with an oscilloscope. On the IN0#_P signal before the Chip I can measure the signal as well as the DC bias voltage. But directly after the corresponding OUT pin there is only the DC bias. No signal is coming out. Do you have an idea what could be the problem?

The AUX lines as well as hotplug work and the monitor is recognized but as soon as the link training begins (guess what) the signal on the main lines don't reach the monitor...The ramp up for the PWD# is triggered several seconds before the device is plugged in and the switching of the "_P" an "_N" as well as the lanes is allowed as long as the differentials are together.

Thanks in advance!

over 4 years ago

0 David (ASIC) Liu over 4 years ago

TI__Guru**** 157496 points

Hi,

Can I please see the full schematic including the TS3DV642?

Thanks

David

0 Heiko Strohmeier over 4 years ago in reply to David (ASIC) Liu

Prodigy 70 points

Hello David,

thank you for your efforts to try to help me. Below you can see the interconnect schematic. I saw that the TS3DV642 requires 1V bias voltage but the maximum is not mentioned in the datasheet. My current DC bias generated by the DP141 is about 2.5V. But I think this is not the problem since I measured between the two devices and there is no signal coming out of the DP141.

One thing I did wrong at first was to leave the PWD of the DP141 floating (since it has a pull up) but then after it didn't work I changed it to the ramp-up circuit. Also there were 10k pull/up resistors and some were directly tied to GND but after it didn't work I changed it to the 1k. However, I think this shouldn't have damaged the DP141...

Best regards

Heiko

0 Heiko Strohmeier over 4 years ago in reply to Heiko Strohmeier

Prodigy 70 points

Oh and here is the power supply:

One DP141 draws about 150mA @2.76V. I started the design with about 2.5V and after it didn't work I increased it a bit to be more in the middle of the supply voltage spec.. but it didn't help.

0 David (ASIC) Liu over 4 years ago in reply to Heiko Strohmeier

TI__Guru**** 157496 points

Heiko-san

Looking at the schematic, where are the rest of DP141 power pins, 6, 7, 10, 13, 19, 22, 25, 26, 29, 32, 38?

Thanks

David

0 Heiko Strohmeier over 4 years ago in reply to David (ASIC) Liu

Prodigy 70 points

Hello David,

they are hidden behind the first one. They are all connected in the layout and every pin has his own 100nF + a shared plane capacitor.

I find it strange that there is a common-mode voltage on the output but literally nothing else happens on the output..

Thanks

Heiko

0 David (ASIC) Liu over 4 years ago in reply to Heiko Strohmeier

TI__Guru**** 157496 points

Heiko-san

You should be using the upstream port connector at the DP141 input. Below is the upstream port connector pinout.

Also, AC coupling caps on the DP141 input are not needed as the AC coupling caps are required to be placed on the transmitter side.

Thanks

David

0 Heiko Strohmeier over 4 years ago in reply to David (ASIC) Liu

Prodigy 70 points

Ah, thanks for the hint.

So when a cable crosses the lanes and I have now two cables they are wrong on the monitor side.

But the source (PC) is connected to the DP141 input. When I can measure a signal at the DP141 input, shouldn't there be an output signal?!

If I cannot resolve this I'll be looking for another part for the next revision..

Thanks

Heiko

0 David (ASIC) Liu over 4 years ago in reply to Heiko Strohmeier

TI__Guru**** 157496 points

Heiko

You should replace the input AC coupling capacitors with 0ohm resistors. Otherwise the total capacitance is outside the DP spec.

Depends on the probe type and the termination of the probe, I would measure the signal at the TS3DV642 output, after the AC coupling caps.

Thanks

David

0 Heiko Strohmeier over 4 years ago in reply to David (ASIC) Liu

Prodigy 70 points

Hello David,

the AC caps on the DP141 inputs were replaced by 0 Rs. But still no luck. The screen of the monitor still stays black after a link training attempt and I cannot measure any signal at the TS3DV642 output. I only see the DC bias from the DP141 there.

I guess it's cursed somehow. Thank you for your efforts!

edit: ok as a last attempt I will try to swap the lanes even though I cannot measure something...

best regards

Heiko

0 David (ASIC) Liu over 4 years ago in reply to Heiko Strohmeier

TI__Guru**** 157496 points

Heiko

With input side connector being the wrong connector, the lane order is not correct and monitor will stay black until the input side connector is fixed first.

Thanks

David

0 Heiko Strohmeier over 4 years ago in reply to David (ASIC) Liu

Prodigy 70 points

Hello David,

yes, you were right. Despite I couldn't measure the signal after the amplifier, swapping the lanes did the trick. It works now. awesome!

Thank you very much for your help!

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SN65DP141: No output signal