TPD6F003: SD interface failures on high frequencies (SDR104 mode)

Andrej Rosano

Part Number: TPD6F003

Hi,

we are using the TPD6F003 to provide the ESD protection for the microSD interface as in the following schematics.

The interface works correctly for low SD speed modes (clock 50MHz) but it starts having issues with high speed modes (~132 MHZ). With such a frequency some microSDs fails to complete the tuning.

Replacing the TPD6F003 with short circuits the interface works correctly as expected also on high frequencies. The datasheet states that the part should sustain frequencies up to 200 MHz.

Is this p/n tested on high frequencies SD modes (e.g. SDR104)? If yes, is there anything we should pay particular attention in our PCB routing?

Thanks

over 3 years ago

0 Matt Smith3 over 3 years ago

TI__Expert 8471 points

Hi Andrej,

What is the value of the resistor on the SD1_CLK_R line?

Regards,

Matt Smith

0 Andrej Rosano over 3 years ago in reply to Matt Smith3

Prodigy 40 points

Hi Matt,

the resistance of R54 on SD1_CLK line is 22 Ohms.

Thanks

Andrej

0 Matt Smith3 over 3 years ago in reply to Andrej Rosano

TI__Expert 8471 points

Hi Andrej,

You can try removing that 22 Ohm resistor, since it can cause signal attenuation. However, if the signal is a square wave, the cuttoff frequency will be lower due to the increased amount of harmonics in a square wave as opposed to a regular sine wave.

I also ran a simulation to confirm this at both 50 MHz and 132 MHz, respectively.

50 MHz

132 MHz

I'm not sure how exactly your signals look, so this was my best approximation. Try removing the 22 Ohm resistor first. If that doesn't work, we may need to look at replacing the device with a non-EMI filter ESD device. Let me know if you have any questions.

Regards,

Matt Smith

0 Andrej Rosano over 3 years ago in reply to Matt Smith3

Prodigy 40 points

Hi Matt,

unfortunately bypassing the R54 does not solve the issue.

Regards

Andrej

0 Sandesh Rawool over 3 years ago in reply to Andrej Rosano

TI__Intellectual 2694 points

Hi Andrej,

We are looking into how to solve this issue. Thank you for the patience.

Regards,

Sandesh

0 Erika Beskar over 3 years ago in reply to Sandesh Rawool

TI__Prodigy 340 points

Hi Andrej,

If the microSD failed to complete tuning at ~132MHz after removing 22 ohms resistor, then the 19pF capacitance of the TPD6F003 added to the board parasitics are distorting the signal to a level that is preventing the tuning from happening properly.

I’ll recommend for you to replace TPD6F003 with TPD6E05U06 (this is a non-EMI filter ESD device).

TPD6E05U06 – It’s also a 6-channel diode, with Ultra-low-capacitance (0.5pF) that will work well for higher bandwidth. Other specs are comparable.

See below:

0 Erika Beskar over 3 years ago in reply to Erika Beskar

TI__Prodigy 340 points

0 Andrej Rosano over 3 years ago in reply to Erika Beskar

Prodigy 40 points

Hi Erika,

understood. Thanks for the advice.

Regards

Andrej

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TPD6F003: SD interface failures on high frequencies (SDR104 mode)