LSF0204: Why does 3.3 V IO have a voltage drop?

Thanks for your comment.

1. As I know LSF has FET but I have no idea why it's a passive switch. Do you mean is that acting like a passive switch?

2. I'm just wondering why it's 20 K ohm.

3. 'Some component' means Network Interface Card or something?

Could you please explain in more detail?

4. Some NICs have an internal pull-up on the PCIE_RESET_N line, but we don't know the value. It was also dropped.

I thought you were talking about FET as a passive component. Sorry, I misread a word as 'a passive switch'.

Then, why TXS0104 does not cause a voltage drop? It also has an internal 10 K pull-up resistor.

here, "passive" means that the I/Os are not buffered.

I do not know why the TXS behaves differently; the LSF and TXS have the same architecture (the TXS just adds internal pull-ups and edge accelerators).

Thanks for your answer.

I've tested without NIC and It was the same result.

It doesn't have anything to do with NIC.

So, please ignore the block diagram.

LSF0204; Added an external 10K pull-up on PCIe_33_RST_N (Still has a large voltage drop (without NIC))

TXS0104(Internal 10K pull-up); No external 10K pull-up on PCIe_33_RST_N (without NIC)

Still wondering why LSF has a large voltage drop even though there's no connection on the B side's IO.

Hi Seunghwan,

When you say no connection on the B side's I/O, do you mean the PCIE connector is disconnected as well?

Note that your schematic seems to indicate the device has no outputs at all, as PCIE_RST and PCIE_33 seems to be both going into the device. Please help confirm for bus contention as the TXS case also seems to be dropping after a longer while, thanks.

Best Regards,

Michael.

Hi Michael,

Thank you for your comment.

No connection on the B side's I/O means the PCIE connector is disconnected.

There's nothing connected to B-side.

I wonder why LSF0204 has a voltage drop on B-sides at the first waveform.  

Because the TXS series does not have a voltage drop. (Please refer to the above capture, RED circle)

It's okay to be dropping after a longer while.

Thank you.

Best Regards,

Seunghwan Lee.

Hi Seunghwan,

Note that the TXS has edge accelerators which speeds up the edges. Would the host happen to have internal pull-downs? 

Best Regards,

Michael.

Yes, the host has an internal pull-down.

But I don't know the specific value.

I knew the TXS series have an edge accelerator. 

But I thought the edge accelerator doesn't affect dropping voltage.

If the level translator has edge accelerators, it influences to the voltage drop?

Thank you, Michael.

It helps a lot!