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LM34936: Handling if the BIAS pin is not used

Dice-K
Mastermind 6500 points
Part Number: LM34936
Other Parts Discussed in Thread: LM5175, LM5176, ,

Hi support team,

What would be the recommended handling if the BIAS pin is not used?
According to WEBENCH, it is connected to GND via 0.1μF.
Shouldn't it be directly connected to GND?

Also, please let me know if VIN's "Series Blocking Diode" is necessary or not.

Please also let me know if these apply to the LM5176 and LM5175 as well.

Regards,

Dice-K

  • +1
    TI__Mastermind 19350 points

    Hi Dice-K,

    Thanks for using the e2e forum.
    If the BIAS pin is not used, I would follow the webench recommendation and connect the pin via a 0.1uF cap to GND. You can see the same structure in the LM34936 EVM schematic. ( https://www.ti.com/tool/LM34936EVM )
    As the pin is connected to the VCC voltage inside the IC, I would avoid shorting this pin to GND directly.

    The series blocking diode is not required and fully optional.
    If this diode is not implemented, please always make sure that the power supply is connected with the correct polarity. If there is no series diode and the poles are connected wrong by mistake, the IC can take damage from the negative input voltage.

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Mastermind 6500 points

    Hi Niklas,
    Thank you for your reply.

    I would like to insert 0.1μF between BIAS and GND to avoid direct connection between VCC and GND.
    (However, since R17 of the LM34936EVM is 0Ω, I think this is an example where VOUT and BIAS are connected.)

    Are the following thoughts about "Series Blocking Diode" correct?
    When VIN is 4.2V or higher and VIAS is 0V, there is no reverse current from VCC to VIN because VIN > VCC.
    Therefore, "Series Blocking Diode" is unnecessary.
    However, if VIN is less than -0.3V of Abs, it will be damaged, so care must be taken with the applied voltage.

    Best regards,
    Dice-K

  • +1 in reply to Dice-K
    TI__Mastermind 19350 points

    Hi Dice-K,

    Thanks for the update.
    I am sorry I did not address this condition in my previous answer.

    You are correct, there should be an internal connection between BIAS and VIN through a diode.
    This means if the BIAS is used and supplied with a higher voltage than VIN, there will be current flowing back to the supply at VIN.
    E.g. if VIN is 4.2V and there is a voltage at BIAS of 6V, the series blocking diode is necessary to avoid this negative current flow.

    Best regards,
    Niklas