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I2C Level Shift with High Speed Mode

Kevin LaRosa
Genius 17380 points
Other Parts Discussed in Thread: TCA9406, TCA9406EVM

Hello,

We were trying to determine if it's possible to level shift using I2C High Speed mode. MSP432 only supports 3.3V I2C operation and our application only supports 1.8V I2C operation so if wanted to test HS mode we'd need to translate it.

My gut is that due to the high speed mode requirement of current sources in the master, level shifting may not be possible.

  • 0
    TI__Guru* 77621 points
    Hey Kevin,

    For high speed mode, what frequency were you targeting?

    For the SCL line, you could probably make the master generate push-pull SCL pulses and use a discrete FET for level shifting. If you don't have an I2C library with the option of push pull on SCL then mu suggestion below should still work.

    SDA will likely be trickier, using a device with a rise time accelerator would probably be necessary for this to ensure the master does not need to sink large current while driving the dat line. I would recommend you give TCA9406 a shot. This device can drive a signal high in about 30 nanoseconds. Though the device was meant to support fast mode plus, I suspect it could actually handle the high speed mode. (Have never tried this but would be happy to hear about your results).

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    TI__Genius 17380 points
    Hi Bobby,

    We would be targeting 3.4 Mbit per second speed. TCA9406 looks pretty interesting and definitely closest I've seen yet. I've ordered an EVM and will try to test it before tape-out.

    An added benefit of this compared to the one we were looking at is that this one appears to be able to do VCCA = VCCB for cases when we want to do 400 kHz 3.3V to 3.3V too which is nice.
  • 0 in reply to Kevin LaRosa
    TI__Genius 17380 points
    Hi Bobby,

    So far so good, it worked for our initial test of blue wiring the TCA9406EVM into our EVM. It was only room temp but for our purposes that should be fine. If we run into any issues when we get the new board back we'll be sure to open a new E2E.