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TCA9545A: Power Sequencing and VIL/VIH specs

Roy Hsu
Genius 9390 points
Part Number: TCA9545A
Other Parts Discussed in Thread: PCA9545A

Hi Team,

I have two questions about the TCA9545A.

1. Am I right in saying that the VIH/VIL specs only apply to the Master SDA/SCL lines and do not apply to the slave SDx/SCx lines?

2.  Will there be an issue if Vcc comes later than the Master I2C signals? Something like Vcc gets back-powered or violating the POR requirement?

Thanks!

Roy

  • 0
    Guru 316860 points

    1. Yes. The TCA9545A's internal I²C slave is connected to the master SDA/SCL pins; it never cares whether the slave lines are low or high.

    2. The absolute maximum ratings and the recommended operating conditions allow voltags above VCC.

  • 0
    TI__Mastermind 47558 points

    Roy,

    1. Am I right in saying that the VIH/VIL specs only apply to the Master SDA/SCL lines and do not apply to the slave SDx/SCx lines?

    You are correct in saying that "the VIH/VIL specs only apply to the Master SDA/SCL lines." The VIH and VIL input voltages do not concern the SDn/SCn pins. 

    2.  Will there be an issue if Vcc comes later than the Master I2C signals? Something like Vcc gets back-powered or violating the POR requirement?

    There will not be back powering issues when VCC powers on later than the Master I2C signals coming in. This was originally a problem with the RESET on the PCA9545A device to VCC. There was a case where if VCC < /RESET, /RESET would back-power on the VCC pin. TCA9545A fixes this situation. 

    Regards,

    -Tyler

  • 0 in reply to Tyler Townsend
    TI__Genius 9390 points

    Thank you, Tyler and Clemens for your comments!

    A follow-up question on item 2. If Vcc comes later, will it affect the incoming Master I2C signals? Such as clamping?

    Thanks!

    Roy

  • 0 in reply to Roy Hsu
    Guru 316860 points

    No; the SDA/SCL inputs a high impedance with any voltage (up to 6 V).