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SN74CBTLV3253: whether the Vin pin will source current to VCC?

Frank Xiao
Genius 12055 points
Part Number: SN74CBTLV3253
Other Parts Discussed in Thread: SN74CB3Q3253

Hi team,

we want to check if the Vin voltage is higher than VCC, whether the Vin pin will source current to VCC? Thanks.

  • 0
    TI__Expert 5660 points

    Hi Frank,

    It sounds like you are asking if SN74CBTLV3253 can back-power the supply rail when VI or VI/O is greater than VCC. I found this tech article that provides more information on how to determine if a device is capable of back-powering. The article states:

    The best way to check for diodes is to look at the absolute max spec Iik and Iok. If current limits are (+/-), then there is a diode to Vcc and Gnd. If there is only a (–) current then there is only a diode to Gnd.


    Checking with the SN74CBTLV3253 datasheet, the absolute max spec for IK and I I/OK (-50mA) is only for conditions when VI and VI/O is negative. According to the tech article:

    In absolute max spec

     

    No clamp to VCC on input or output:

    This device cannot be back powered

    So, SN74CBTLV3253 is not capable of back-powering the device or supply rail. This does not mean that the device is protected from damage. This device supports rail-to-rail switching only on I/O ports. VI/O or Vin greater than VCC may cause permanent damage to the device; functional operation is not implied.

    I would also like to point out this device does have powered-off protection. Meaning, when Vcc = 0V and VI/O is greater than 0V, the switch will keep the high impedance state and no damaging current can flow through the switch AND the supply will not be back-powered. This feature only applies when the device is powered off (VCC = 0V).

    May I ask what your application is for which you are concerned about input voltages greater than the supply? Are you asking about select/enable input pins or I/O channel pins? TI offers several switches that support input voltage beyond supply. It looks like SN74CB3Q3253 may be an appropriate fit for you, as it supports powered-off protection as well as input voltage beyond supply. This is due to the charge pump architecture of the switch.

    Let me know if this answers your question or if you have any follow-up questions! I'd like to know what you think about implementing SN74CB3Q3253 in your system.

    Best regards,

    Kate