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TPS7A8300: BIAS pin termination question

Darren (FAE)
Expert 5483 points
Part Number: TPS7A8300
Other Parts Discussed in Thread: TPS7A83A,

If VIN is used with an input >1.4V, can the BIAS pin be left floating?
Would there be any issues if the BIAS pin was tied to GND (0V) if VIN>1.4V?

  • 0
    TI__Expert 5231 points

    Yes, it is advised for the bias pin to be left floating if Vin > 1.4. I also just connected the bias to GND in the lab when Vin >1.4 and I saw no change in the output voltage. Please let me know if you have any more questions.

    Thank you,

    Josh Nachassi

  • 0 in reply to Josh Nachassi
    TI__Expert 5483 points

    Hi Josh, 

    There is a device I found, the TPS7A83A.
    Looking at the functional block diagram, both the TPS7A83A and the TPS7A8300 show an identical internal connection structure for the BIAS pin.

    There is an internal switch that uses BIAS until VIN goes above 1.4V, then it switches to using VIN.
    Because of this, BIAS is only left connected to the internal UVLO structure.

    The TPS7A83A datasheet actually includes the comment "this pin must be left floating or tied to ground."
    My customer has several different designs with this device, and would prefer to follow the TPS7A83A recommendation to tie to GND.

    If possible, I would like to provide a comment (from TI) that tying BIAS to GND is also an acceptable termination scheme for this pin on the TPS7A8300. Would you agree with that statement?

    Regards,
    Darren

  • 0 in reply to Darren (FAE)
    TI__Expert 5231 points

    First and foremost, the TPS7A8300 and the TPS7A83A have some similarities but are two different devices. My test yesterday was with the tps7a8300 and I tied Bias to GND and I was getting the same output voltage as if I left it floating when Vin > 1.4v. I also tested only 1 unit and only tested for output voltage and not the other specs in the data sheet. 

    Since the data sheet specifically states that you can tie bias to gnd or leave it floating in the TPS7A83A I think that would be the most suitable device for your customer based on there design. 

    Please let me know if you have any further questions.

    Thank you,

    Josh Nachassi