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LM76003: 24V BIAS input

Oba
Genius 17335 points
Part Number: LM76003

Hello,

 

I want to use LM76003 with 28V input and 24V output.

They I want to ask about BIAS pin usage.

 

The datasheet(SNVSAK0) says “TI recommends trying this to Vout when 3.3V =< VOUT =< 18V….” in Page 4 like the below.

Why up to 18V?

On the other hand, the same datasheet says “TI recommends that the BIAS pin be connected directly to Vout when 3.3V =< VOUT =<24V…” in Page 23 like the below.

 

Which is correct?

 

My question is I want to connect BIAS to 24Vout. Is it OK and does it make sense?

 

Regards,

Oba

 

 

  • 0
    TI__Genius 11040 points
    Hello,

    The Abs Maximum of the Bias pin is 30V or VIN. This would be okay in terms of the pin, but there will be little benefit at 28V to 24V conversion. The internal LDO will powered by the Bias pin if connected or the input if the Bias pin is floating. If there is a downstream power rail at 3.3V or 5V, then there will be more of an efficiency gain to power the internal LDO from a low voltage rail.

    Please let me know if you have any additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    TI__Genius 17335 points

    Hello Katelyn,

     

    Thanks for your reply.

    So the user can input up to 24V if it is lower than VIN+0.3 as the datasheet says on the recommended operating condition on page 5 although it doesn’t have so much benefit. Correct?

     

    In my case, I want to connect BIAS to 24V VOUT. Because of VOUT accuracy and transient response, it may be over 24V a little bit. In this case, I think we just can’t guarantee operation if BIAS is over 24.0V. So what kind of problems could happen when BIAS is over 24V a little bit? 

     

    Regards,

    Oba

  • 0 in reply to Oba
    TI__Genius 11040 points

    Hello,

    The issue will be that you do not want the BIAS to ever see an overshoot that would be above the absolute maximum or the VIN.  This could cause damage to the Bias circuitry.

    Best Regards,

    Katelyn

  • 0 in reply to Katelyn Wiggenhorn
    TI__Genius 17335 points

    Hello

    Thanks.

    Katelyn I know if it could be damaged if BIAS input is over abs MAX.
    My question is for the case if BIAS voltage is over 24V but less than abs max that is over recommended operating condition and less than abs max.

    Regards,
    Oba  

  • 0 in reply to Oba
    TI__Genius 11040 points

    Hello Oba,

    The bias voltage up to 24V has been tested in terms of reliability and functionality.

    If the bias voltage is between 24V and abs maximum then there will not be any immediate damage.  The risk is that the lifetime will be degraded.

    Please let me know if you have any additional questions or if anything is unclear.

    Best Regards,

    Katelyn

  • 0 in reply to Katelyn Wiggenhorn
    TI__Genius 11040 points

    Hello,

    Thank you for your e-mail.  I am going to close this thread, and if you have any additional questions, please continue the conversation over e-mail.

    Thank you,

    Katelyn