TXS02612: SDIO waveform issue on CLKB1 pin

Stefano Asiri

Part Number: TXS02612

Tool/software:

Hi all,

I have designed a system in where SDIO signals for uSD-CARD need to be shifted from 1V8 to 3V3 in DS mode (25MHz) or HS mode (50MHz).

From debbugging, we found a problem on the waveforms.

This is part of my schematic:

This is the waveform at 25MHZ (SDIO0_SDCLK in RED and SDIO0_SDCLK_CARD in YELLOW)::

As can be seen, there is some sort of overshoot between 1.5 and 2 V on the output signal at 3.3 V (yellow).

The same at 50MHz:

And at 195KHz:

The SDIO BUS signal traces are made with an impedance of 50Ohm and the same length.

Do you have any advice to explain this behavior?

(Teledyne ZS1500 and HFP1500 active probes were used for these measurements.)

thank you in advance for the support.

Best regards.

Stefano Asiri.

over 1 year ago

+1 Jack Guan over 1 year ago

TI__Mastermind 40006 points

Hey Stefano,

How long is the SDIO BUS trace lengths? Can we ensure that output cap. load is kept a minimum as possible, similar to that mentioned in section 4 of this app note: A Guide to Voltage Translation With TXS-Type Translators? If possible, please also test with tip & barrel probe to minimize ground loop during testing.

In any case, is the non-monotonic rising/ falling edge causing data corruption?

Regards,

Jack

0 Stefano Asiri over 1 year ago in reply to Jack Guan

Prodigy 30 points

Hi Jack,

The total length of the SDIO BUS trace is 192 mm. All the measurements I have shown are already with ground loop minimization, but they were made on approximately half of the traces.
I replicated the measurements close to the SDCARD and this is the waveform:

The undershoot is quite pronounced at the falling edge. Perhaps I can try to reduce it with a 22 ohm series resistor near the TXS02612 chip. Our system has some communication problems with the SD-CARD.

+1 Jack Guan over 1 year ago in reply to Stefano Asiri

TI__Mastermind 40006 points

Hey Stefano,

Yes, trying out various values of series impedance at the outputs of the TXS02612 which are facing the transmission line should help dampen the existing under/over shoots. It is explained further in detail per this [FAQ] What happens when I connect a logic device's output to a 50 ohm transmission line?

If possible, please reduce the cabling/ PCB trace length to be as short as possible for the high freq. data to propagate through without the transmission line effects.

Regards,

Jack

+1 Stefano Asiri over 1 year ago in reply to Jack Guan

Prodigy 30 points

Hi Jack,

with a series resistor I reduced the problem on the CLK, but the error persisted. I finally found that the signal causing communication problems was the CMD during the initialization. I solved the problem by inserting a 1kOhm pull-up on this signal.

Thank you for your support.

Logic

Logic forum

TXS02612: SDIO waveform issue on CLKB1 pin