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CD74HC4067: Not enough power to multiplex sim_vcc, looking for recommendations.

Cho
Prodigy 80 points
Part Number: CD74HC4067
Other Parts Discussed in Thread: TXS02326A, TXS02324, TMUX1574

I'm trying to multiplex two sim card using CD74HC4067 and the signal wires (IO/CLK/RST) are currently working. I know there are other chips that can do this but I can't use the built in LDO because my baseband drives the SIM_VCC power already. Can you recommend me a multiplexer/product that can handle switching VCC lines that are coming from my baseband? 

My other solution was run power to both sim cards and keep the signals pulled down when not in use but I believe the baseband will struggle driving the capacitors at each sim connector.

  • 0
    TI__Mastermind 24440 points

    Hello cho,

    1.Can you tell me what LDO  and baseband stands for?

    2. Can you tell me the voltages of the vcc lines?

    3.Can you send over a schematic over design?

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 80 points

    Hi Kameron, 

    1. Baseband is my GSM modem and the LDO is the low dropout voltage regulator that some dedicated sim mux chips have built in for regulating the power to the sim card (ex: TXS02324, TXS02326A) but my GSM module does that for me already.

    2. I'm supplying 5v power to the mux. The GSM modem then provides 1.8v power to each sim card connector.

    3. 

    In the diagram above, I am providing power to SIM1_CONN and SIM2_CONN from the GSM module using the SIM_VCC pin. I want to be able to multiplex the SIM_VCC line because each sim card connector has a 100nF capacitor and the module might not be able to power both capacitors at the same time. I can't use another CD74HC4067 to switch the VCC line because it doesn't have enough current.

    I will be switching to a 4 channel (TMUX1574) as I don't need a 16 channel but the CD74HC4067 breakout is readily available.

  • +1 in reply to Cho
    TI__Mastermind 24440 points

    Hello,

    I agree that the TMUX1574 is the right device for this application. 

    I also wanted to let you know that both of these devices are passive muxes and therefore cannot add or redrive the signal.

    The Tmux1574 if powered at 5v will be able to multipex the sim vcc line. It is bidirectional so you can feed the vcc signal into the d pin of the mux and use control pins to select which sim card to send vcc to.

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 80 points

    Just out of curiosity, I have a TMUX1574 breakout board in development with a ~2-3 week lead time. What can be used to help the CD74HC4067 chip drive the vcc signals? If I have components laying around, I would like to try to still get this to work.

  • 0 in reply to Cho
    TI__Mastermind 24440 points

    Hello Cho,

    There are multiple breakout boards for the TMUX1574 that are available and they might have less lead time.

    Cho said:
    I can't use another CD74HC4067 to switch the VCC line because it doesn't have enough current

    I believe if not having enough current is your issue you could use a noninverting buffer to redrive the signal coming out of the mux.

    Regards,

    Kameron