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About BIAS PIN of LM536033

watanabe
Expert 1740 points
Other Parts Discussed in Thread: LM53603

Hi,


Mycustomer has three questions about [9.2.2.6 BIAS] of LM53603 datasheet.
=======================================================

Q1.
Is it possible to Vout is BIAScurrent any 3.3V or 5V is below 100mA by adding the resistance of 3Ω ~ 5Ω between Vout and BIAS.
I think that there is a inside circuit to limit to 100mA.
Could you tell us about it?

Q2.
When BIAS Current is 100mA, there is a voltage drop of 100mA * 5ohm = 0.5V.
When Vout = 3.3V, but is considered to Vbias is 2.8V What no problem?

Q3.It is written by datasheet.
"In severe cases, a Schottky diode can be placed in parallel with the output to limit the transient voltage and current."
Is not the problem in such a connection of attached image?
Could you tell us about the recommended value of the rated voltage and rated current and VF of the Schottky diode.

=======================================================
I'm looking forward to advice from you.
Best regards,


Watanabe

  • 0
    TI__Intellectual 2225 points

    Watanabe-san,

    Here are my responses to your questions:

    Q1:

    The BIAS current only powers the control circuitry and gate drives inside the LM53603.  The maximum current consumed by the control circuitry will stay well below 100mA.  It will not exceed 25mA.

    Q2:

    Because the current is less than 25mA, there should be no problem. 

    Q3. 

    The placement in the image is incorrect.  The Schottky diode should have it's cathode connected to the BIAS pin, and the anode connected to GND.  The purpose of the Schottky diode is to prevent the BIAS pin from going negative.  A 10V, 100mA with Vf= 0.5V  Schottky should be enough for most cases, but the exact amount needed will depend on the inductance of the load when it becomes shorted and how much output capacitance there is.  

    Thanks,

    Perry 

  • 0 in reply to Perry Tsao96839
    Expert 1740 points
    Perry-san,

    I appriciate for your reply.
    My customer was able to new question.

    Q1.
    I read[The maximum current consumed by the control circuitry will stay well below 100mA].
    If why should be connected the resistor(value in the range of 2~5ohm)?

    Best regards,

    Watanabe
  • 0 in reply to watanabe
    TI__Intellectual 2225 points

    The resistor Rbias and the capacitor Cbias connected to the BIAS pin create a low-pass filter that helps keep noise on the output voltage from affecting the internal LDO that powers the control logic from the BIAS pin.

    Perry

  • 0 in reply to Perry Tsao96839
    Expert 1740 points

    Perry-san

    Thank you for the quick reply.
    I’m looking forward to doing business with you.


    Watanabe