TXB0304: Not able to drive PCIe Clock request ( CLKREQ#) signal

Nimesh Rana

Part Number: TXB0304
Other Parts Discussed in Thread: TXS0104E, , LSF0204

Hello Team,

We are using TXB0304RUTR level shifter for driving PCIe CLKREQ# signal which connected to PCIe based WLAN module. In module pin is defined as open drain, and suggesting to add pulled up at host side.

Below is our implementation in schematic.

While powering on we are not getting any activity on any side of level shifter for PCIE0_QCA_WL_CLK_REQ_N and due to that link initialization of PCIe is failed. We have checked enable voltage is coming high so seems no issue of enabling level shifter. Even though we have added 10k pulled up on Side A signal, still behavior remains same.

During further debugging, we have replaced TXB0304RUTR level shifter by TXS0101YZPR and WLAN we can see transition on PCIE0_QCA_WL_CLK_REQ_N line and able to do link initialization.

Can you please help us:

1) What is the major difference between TXB0304RUTR & TXS0101YZPR Level shifter?

2) Is there any timing difference for TXB0304RUTR which can cause issue for CLKREQ# line?

3) What can be other cause for TXB0304RUTR for above mentioned issue?

4) To eliminate HW change and PCB Re-spin, can you please help how we can drive signal with TXB0304RU?

Your Prompt reply is highly appreciated.

Regards,

Nimesh

over 4 years ago

0 Nimesh Rana over 4 years ago

Intellectual 440 points

Non Working Circuit:

Working Circuit:

0 Clemens Ladisch over 4 years ago

Guru 278340 points

Your questions are answered in section 8.4.2 of the datasheet. You cannot use the TXB in this application.

0 Nimesh Rana over 4 years ago in reply to Clemens Ladisch

Intellectual 440 points

We have tried with 100K resistors pulled up at both side, still same behavior we found.

Regards,

Nimesh

0 Chad Crosby over 4 years ago in reply to Nimesh Rana

TI__Expert 6680 points

Hi Nimesh,

You'll need to switch out U15 in the non working circuit for a TXS0104E. That should solve your problem.

Edit: If this is not an option for you, could you post some waveforms of the inputs & output pins so we can start the troubleshooting process?

Thanks!

Chad Crosby

0 Nimesh Rana over 4 years ago in reply to Chad Crosby

Intellectual 440 points

Hello Chad Crosby,

Thanks for your input. Suggested new part is not feasible to mount in existing board due to FP mismatch.

I found another pindrop solution IC, LSF0204RUTR which is Open drain type and tested same part but still facing same issue.

It will be good of you can help to solve issue with LSF0204RUTR. Please provide your suggestions for

LSF0204RUTR.

Regards,

Nimesh

0 Chad Crosby over 4 years ago in reply to Nimesh Rana

TI__Expert 6680 points

Hi Nimesh,

I'll need to see some waveforms close to the device in order to troubleshoot more. If you're not able to provide scope shots of the LSF translating, you could provide them for the TXB0304.

For designing around the LSF family of translation devices, please see our Logic Minute video series: https://training.ti.com/node/1139264

Thanks!

Chad Crosby

0 Nimesh Rana over 4 years ago in reply to Chad Crosby

Intellectual 440 points

Hello Chad Crosby,

Sorry for late reply.

We did following rework:

In above non working circuit we have replaced u15 from TXB to LSF0204 and removed other R173, R174, R175 & R172.

With above rework we are observing signals with 1.8V level at 3.3V side same as Vref A side (1.8V) not 3.3V level.

WL_EN and BT_EN are GPIOs driving by host and it is push pull type. Internally configured as pulled down.

Can you help us why we are not getting 3.3V level signals? Any configuration change required in FW or Any pulled up required?

As per our understanding as this GPIO push pull type so no need of pulled up, but yes you can correct us if we wrong.

Regards,

Nimesh

0 Clemens Ladisch over 4 years ago in reply to Nimesh Rana

Guru 278340 points

The LSF requires pullups on all pins that can be outputs. See section 5.2 of Voltage-Level Translation With the LSF Family.

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TXB0304: Not able to drive PCIe Clock request ( CLKREQ#) signal