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Hi,
Part of our testing activities include booting EVMs (evaluation modules) from SD cards and maintaining a board farm of about 160 boards. We have been working on developing an SD card mux boosterpack for the MSP432 launchpad so that we can flash SD cards remotely on test boards. Having the boosterpack working would make our lives much easier as it would allow us to change the bootloader at will and also recover boards with a bad bootloader without having to physically remove the card flash and re-insert it. We created version 1 of the boosterpack based on the TS3A24159 mux (info available at arago-project.org/.../ and we started noticing issues with UHS-I and higher speed cards. After taking a closer look at the datasheet we noticed that the TS3A24159 is speced for upto high speed cards only. Since some of our boards can support UHS-I cards we started working on version 2 of the board and are looking for a mux that would work for UHS-I and higher speeds cards. Browsing around the e2e blogs we came across https://e2e.ti.com/support/switches_multiplexers/f/388/p/448105/1611517#1611517 and would like to get your feedback on the mux part to use and other design recomendations you may have.
We also noticed problems with EVMs that included ESD protection chips (http://www.ti.com/product/TPD2E001/datasheet/abstract#SLLS6847061) and had to disconnect them from the circuit when we use our SD mux card.
We appreciate any info you can provide.
Thanks and regards,
Alejandro Hernandez
Alejandro,
Bandwidth performance of a signal path is highly dependent on the layout. Please be sure you are using high speed layout best practices.
The TS3A24159 device hast a bandwidth of 23MHz which should be able to handle ~15Mbps (SD Normal speed), start to become marginal at SD high speed (25Mbps), and not be suited for UHS-1 and faster.
We recommend our switch bandwidths based on the formula data rate x (3/2) which provides some margin about the theoretical minimum data rate x (1/2). For example UHS is 104Mbps we would like to find a switch with >156MHz bandwidth. You can see more information on bandwidth vs datarate on the switches and multiplexers FAQ page below.
[FAQ] More Frequently Asked Questions about signal switches and multiplexers - Switches & multiplexers...
For more answers to your questions, check out the new FAQ page ! This page features a growing list of similar and frequent questions asked about TI's multiplexers
Here is a list from TI.com switch selection tool for 1:2 switches sorted with bandwidth greatest to least. You would need to select a switch with the appropriate bandwidth for the type of SD card application you would like to support.
