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AM5746: UHS SD Card and MMCHS_AC12[21:20]DS_SEL Clarification

Mari Tsunoda
Expert 3705 points
Part Number: AM5746

Hi Team,

One of my customer is trying to use a UHS SD Card and has a few questions regarding the MMCHS_AC12[21:20]DS_SEL bit field. 

1) When using the UHS SD card, do they need to change this bit to a specific driver strength. If so, is there anything in the datasheet/TRM/any other document that they can reference for what and why it needs to be changed?

2) How are the driver types (A, B, C, D) different? Is there also other documentation that explains this?

3) By changing the value in the bit field DS_SEL, what changes? (ie. power?)

Best regards,

Mari Tsunoda

  • +1
    TI__Genius 10180 points

    Mari,

    Typically Driver Type B (Default Configuration) is the setting customer will use.  This is defined as the 50 ohms nominal driver.  If the customer has different impedance on their board, then they may need to consider the other driver types.  Driver Types A, C, D are defined in the SD specification as 33 ohms nominal, 66 ohms nominal, and 100 ohms nominal, respectively.  Changing the driver type may also be beneficial if customer has a specific slew rate they are targeting.  You can refer the customer to the specification for more information.

    Best Regards,

    Shiou Mei

  • 0 in reply to Shiou Mei Huang
    TI__Expert 3705 points

    Hi Shiou,

    Thank you! Will mark this as resolved.

    Best regards,

    Mari