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TXB0104: Require Help to design a microSD card in SPI mode circuit

Anmol Saxena
Prodigy 40 points
Part Number: TXB0104

Hello Dear TI Community,

I am trying to design a PCB board for MicroSD Card application. I want to use the microSD card in SPI Mode.

Now my microSD card is working at 3.3V and my microcontroller is operating at 1.8V, because of which I have used the voltage level shifter TXB0104 IC for shifting 1.8V at VCCB side to 3.3V at VCCA side. I have attached my circuit schematic herewith.

Legend for my circuit:

BOOST_OUT= 3.3V

BUCK_OUT= 1.8V

I require help to check if my schematic is correct. Specific doubts that I have are:

1. Do I need to pull up all the Data Lines (DAT0:3) to BOOST_OUT (aka 3.3V)?

2. Do I need to pull up my CS to BOOST_OUT?

3. Is my connection for OE correct?> The datasheet "TYPICAL APPLICATION" section mentions pulling the OE pin down via a 100k ohm resistor

4. Are my SPI Mode pin configurations correct for the SD Card socket? I have r

efered to the SanDisk microSD datasheet (https://www.alliedelec.com/m/d/04db416b291011446889dbd6129e2644.pdf)

I know that my queries are somewhat inclined towards the usage of microSD card in SPI mode side, but I hope that you will be OK to help me!

  • 0
    TI__Guru 58620 points

    Hi Anmol,

    The TXB0104 is autobidirectional device which supports SPI interface. You initially mentioned that the Vcca is 3.3V and Vccb is at 1.8V. The TXB device doesnt support Vcca>Vccb. 

    The required condition is Vccb>= Vcca as mentioned in the datasheet.

    In the connection, however, I see that Vccb is at 3.3V and Vcca is at 1.8V, which is ok.

    OE pin may or may not need a weak pulldown. If the device needs to be always enabled, then it can be tied to Vcca. I would advise not to have caps added on it though.

  • 0 in reply to ShreyasRao
    Prodigy 40 points

    Thank you for your response Shreyas.

    Sorry, I did write the VCCA and VCCB values incorrectly in my post, but my circuit is correct.

    VCCB> VCCA.

    I want to control the enable pin on my microSD card module and have therefore pulled down the OE pin via 100k ohm resistor.

    I will delete the cap if it will cause issues.

    Would be great if you could help me understand if the CS and all the Data Pins must be pulled up to 3.3V (BOOST-OUT) as well! Just that one tiny doubt floating around in my mind!

  • 0 in reply to Anmol Saxena
    TI__Guru 58620 points

    Anmol,

    please delete the cap since OE needs to match the transition rate of 10ns/V.

    It is not necessary from the device point of view that the IOs need to be held high. however, if the system needs it to be at default high, then I will suggest to use a very weak pull-up (100k or so), so that it wouldn't cause a voltage divider with the internal 4K resistor.

    Refer to the app note:

    www.ti.com/.../scea054a.pdf