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TCA9617B: VCCA and pull up voltage are different

[FAE] Andrew Wang
Genius 10685 points

Part Number: TCA9617B
Other Parts Discussed in Thread: TCA9617A

Hi Team,

Customer is asking if VCCA 3.3V and pull up 5V setting can cause device damage risk for long term usage? Thanks.

Andrew

  • 0
    TI__Mastermind 25046 points
    Hello Andrew,
    I will have to ask design if this is going to be a problem. Why are thy doing this? This is an error on their part, correct? I would be concerned if they back bias into the 3.3V supply via the pullup resistor at 5V. That could potentially cause the 3.3V supply to go above 3.3V and if their are devices on that 3.3V rail that only have 3.6V max voltage, that could raise the voltage above what the other devices on that supply rail is rated for and cause damage to that.

    Did they have a reason to do it this way? It should be fixed in my opinion.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Genius 10685 points

    Hi Francis,

    Thanks for quick feedback.

    I will try to understand the reason behind after reaching customer and update to you later.

    I'm just curious, for TCA9617B, if pull up voltage 5V is higher than supply voltage 3.3V, could be any risk of damage. Please kindly check for me.

    I thought, the internal ESD diode usually can survive below 10mA, pull up resistor of 4.7K ohms should be big enough to limit this current into device whenever over voltage happen, is it reasonable to you?

    Thanks.

    Andrew

  • 0 in reply to [FAE] Andrew Wang
    TI__Mastermind 25046 points
    Hello Andrew,
    It should not get damaged because the pullup limits the current, but they are operating it outside the intended application space and it is not advised. It might adversely affect the life time of the part because the current path being used wasn't designed to be operated like this.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Genius 10685 points
    Hi Francis,

    Thanks.
    Customer told me, this is one of communication port for their battery tester. VCCA has both 3.3V and 5V option, customer doesn't want to set to 5V as default, due to potential of damaging external device when other device VCC set to 3.3V, so decided to set VCCA to 3.3V as default and wish our TCA9617B is strong enough to handle this current. (pull-up 820 ohms, around 6mA.)

    Thanks.
    Andrew
  • 0 in reply to [FAE] Andrew Wang
    TI__Mastermind 25046 points

    I double checked.  The TCA9617B is ok to do this. It doesn't have an ESD devices that can be back biased into Vcc under those conditions.  The TCA9617A does and you would have be careful with that part if you did this.  You are good to go with the TCA9617B.

    -Francis