• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 1566 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM53602: Vcc capacitance(Cvcc) and bias pin

Hirotaka Matsumoto
Guru 27585 points
Part Number: LM53602

Hi all

Would you mind if we ask LM53602?

<Question1>
On the P22 datasheet, it shows "This output requires a 3.3-µF to 4.7-µF, ceramic capacitor connected from VCC to GND for proper operation. An X7R device with a rating of 10 V is highly recommended."
Including DC bias, size and Temperature characteristics, does it require 3.3uF to 4.7uF?
Or, with X7R size=1206, does it require 3.3uF to 4.7uF?(actual value will be 2.7uF?)
And about Cbias, is the same as Cvcc?

<Question2>
Our customer uses the device with Vin=17V to 32V.
If Vin connects to bias pin accidentally, is the bias broken because of over absolute maximum ratings, right?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Guru 72055 points

    Q1:  The 3.3uF to 4.7uF is the rated value of the capacitor.  Yes it will be less with bias; this is OK

    Q2:  Yes, the BIAS will be damaged with a voltage greater than the abs max rating of 16V.

  • 0 in reply to Frank De Stasi
    Guru 27585 points

    Frank san

    Thank you so much for your reply!

    In relation to <Question2>, we have  additional question.
    On the following circuit, if Bias pin connects to VIn(17V to 32V), Bias pin will be broken.
    So, regardless of Bias pin, in this case, what will Rbias be? Broken?
    (For example, Rbias=3Ω, if current flows 1A, power dissipation will be 3W, As the result, Rbias will burn.)
    And then, if Bias pin connects to GND, what will Rbias be? Broken?
    20170529_LM53602.pdf

    If you have some assumption, could you give us?

    We appreciate your help.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Guru 72055 points

    The current in the bias input should not be more than about 12mA to 14mA, approximately.

    It is the bias current for the control circuits and the gate charge current for the MOSFETs.

  • 0 in reply to Frank De Stasi
    Guru 27585 points

    Frank san,

    Thank you so much for your help always!
    We have additional questions about Rbias.

    Our customer has to check the test which connects Bias pin to GND.
    This purpose is to check the safety at any cases and no burning.

    The condtion is Vout=5V/1A, Vin=18V.
    If the Rbias is 3ohm, power dissipation will be 3W.So Rbias will burn.
    In order to prevent buring, we think 2 methods as follows;

    <Method1>
    Rbias = 0ohm.
    Is it possible to use with Rbias = 0ohm?
    According to changing Rbias value(3.0ohm->0ohm), we guess that the reliability for "the bias current for the control circuits and the gate charge current for the MOSFETs" will be reduced.(Because of no RC filter)

    <Method2>
    Inserting the fuse(like as Poly switch) between Bias pin and RBias.
    We think it is possible to protect the RBias burning.
    As the result, control circuits and the gate charge current for the MOSFETs will stop.

    We appreciate your help always!

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Guru 72055 points

    The RC filter on BIAS is only needed if there is the possibility of the output voltage going below ground during a hard short cicuit.

    If it is possible in your application that the output might be hard shorted to ground, and the output rings below ground, and the BIAS is

    connected to VOUT, then the RC filter is recommended.  Otherwise it is not needed.

    Protecting the BIAS R with a poly fuse is OK.

    Grounding the BIAS pin is also OK; there will be some slight loss of low current efficiency.