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TCA5405: I/O expander compatibility with mux input logic levels

Kate Dickson
Expert 5660 points
Part Number: TCA5405
Other Parts Discussed in Thread: TS3DS10224, , TCA9534, TCA6408A

E2E,

I am looking for an I/O expander with at least 5 bits. The supply voltage is 3.6V, and I want to make sure that the VOH/VOL levels are compatible with the mux's (TS3DS10224) VIH/VIL.

I was looking at TCA5405, but I noticed that the VOH at 3.6V supply is 2.5V, which is lower than the VIH of the mux (shown below). 

The min VIH is 0.75 x 3.6V = 2.7V.

Could you recommend an I/O expander with at least 5 bits that has a VOH larger than 2.7V?

Thank you!

Kate

  • 0
    TI__Guru 56780 points

    Hey Kate,

    The TCA5405 is a proprietary interface, so to double check, do you need a single wire i/o expander interface? Or is an I2C i/o expander okay? Is size a concern?

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    TI__Prodigy 480 points

    HI Bobby,

    I am working with Kate on this as well. I2C is the prefered now, but can you clarify what "single wire" interface would be?

    Size and cost are two top concerns for 5 extra I/o and 7 extra I/Os (TCA9534?)

    Thanks,

    Arash

  • 0 in reply to Arash Sabet-Payman
    TI__Guru 56780 points

    "I2C is the prefered now, but can you clarify what "single wire" interface would be?"

    It's what the TCA5405 uses. One wire used to interface with the device.

    For 5 i/os, you could probably still use the TCA5405 since the VoH of the device will likely meet the T3DS10224 requirements (the select pins are inputs which don't draw much current so VoH of the TCA5405 will likely be close to supply.

    For the 7 i/o TCA6408A for the size. We don't have an I2C i/o expander which has 5 I/Os, you would need to size up to 8 I/Os.

    -Bobby

  • 0 in reply to BOBBY
    TI__Prodigy 480 points

    Hi Bobby,

    I apologize. Can you explain what a 1 wire interface is exactly? Is it just a single lane GPIO conection?

    Thanks,

    Arash

  • 0 in reply to Arash Sabet-Payman
    TI__Guru 56780 points

    Hi Arash,

    SPI is a 3 wire interface if you exclude the chip select (MISO, MOSI, CLK)

    I2C is a 2 wire interface (SDA/SCL)

    TCA5405 uses a 1 wire interface (it has no name which is why I keep refering to it as one/single wire) and an example can be seen in figure 2 of the datasheet in which DIN is toggled. There are trade-offs for each interface (speed, routing complexity, redundancy)

    -Bobby