LSF0108: Using LSF0108 to do the buffer in SDIO interface, is it ok?

Eggsy Pang

Part Number: LSF0108
Other Parts Discussed in Thread: TCA9800, SN74AXCH8T245, SN74AUC244, SN74LVC245A

Hi team,

Due to SDIO interface‘s long trace between processor and SD card, customer plan to use a bi-direction buffer(3.3V<->3.3V). The clk max frequence is 100Mhz.

May I know LSF0108 is a good device to realize it? If not, may I know other solutions?

Thanks!

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316640 points

The LSF uses passive switches and is not a buffer.

Devices like the TCA9800 have bidirectional buffers, but they work only at I²C speeds (100 kHz). As far as I know, it is not possible to buffer bidirectional 100 MHz signals.

0 Eggsy Pang over 5 years ago in reply to Clemens Ladisch

TI__Expert 4985 points

Hi Clemens,

LSF belong to Voltage level translation.

May I know if Voltage level translation can improve signal when interface‘s long trace.

Thanks!

0 Dylan Hubbard over 5 years ago in reply to Eggsy Pang

TI__Mastermind 45725 points

Eggsy,

If the signal is going from 3.3 V to 3.3 V, its not translating voltages. As Clemens stated, this is not a buffer so it won't do anything to the signal other than just pass it through. You need a high speed bidirectional redriver which we don't have in our portfolio. I would check with the high speed clocking team.

0 Eggsy Pang over 5 years ago in reply to Dylan Hubbard

TI__Expert 4985 points

Hi Dylan,

How about sn74axch8t245?

Thanks!

0 Eggsy Pang over 5 years ago in reply to Eggsy Pang

TI__Expert 4985 points

Hi Dylan,

The distance between Processor and SD card is 30-35cm, which means SOIO trace is 30-35cm.

May I know buffer is enough rather than redriver, like SN74axch8t245?

Thanks!

0 Clemens Ladisch over 5 years ago in reply to Eggsy Pang

Guru 316640 points

The SN74AXCH8T245 needs direction signals. Does your SDIO interface have such signals?

0 Eggsy Pang over 5 years ago in reply to Clemens Ladisch

TI__Expert 4985 points

Hi Clemens,

I need to check with customer if it have available gpio to control pin.

If there is gpio, can sn74axch8T245 deal with this issue when trace is 30-35cm?

If there is not available gpio, can we use two SN74AUC244 to deal with it? One is for A->B and another is for B->A.

Thanks!

0 Clemens Ladisch over 5 years ago in reply to Eggsy Pang

Guru 316640 points

Is the SDIO protocol handled with a hardware module or in software? In the former case, using a GPIO will not be possible. In the latter case, the SN74AXCH8T245 will be able to do the buffering (but a plain transceiver like the SN74LVC245A would work just as well).

The '244 devices would need the same GPIOs to control their OEs; or without those, you would get bus contention.

0 Eggsy Pang over 5 years ago in reply to Clemens Ladisch

TI__Expert 4985 points

Hi Clemens,

It makes sense.

Unluckly, SDIO protocol handled with a hardware.

So does it not other way?

BTW, just for learning, What situation use Redriver and what situation use buffer? If the trace long is <30cm, buffer can handle it, right?

Thanks!

0 Clemens Ladisch over 5 years ago in reply to Eggsy Pang

Guru 316640 points

In general, bidirectional buffers are not possible because a chip cannot decide which side is input and which side is output. If a chip sees different voltages on both sides, how should it decide which one is the correct one and must be driven to the other side? (The TCA9800 relies on the fact that I²C drivers are open-drain outputs, i.e., that only low voltages are actively driven.)

"Redriver" and "buffer" are mostly the same thing (although some buffers handle analog signals). Redrivers are usually optimized for a certain frequency and line impedance.

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LSF0108: Using LSF0108 to do the buffer in SDIO interface, is it ok?