How do I bootstrap this IC?

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lazzer408

lazzer408

Member
2010-09-12 1:44 am
Chicago
  • #1
    The IC in question is in the link here.

    There may be a better IC to use but I don't know which.

    I'm building a buck converter to reduce 14v to 6v. I'd like to use an 8-pin pwm IC and external mosfet to increase it's current. Is there a way to use pin-1 (collector) and bootstrap the output to drive an N-ch mosfet?
     
    lazzer408

    lazzer408

    Member
    2010-09-12 1:44 am
    Chicago
  • #4
    I don't think so as long as it can drive a mosfet gate. I need 6A of current from my converter so I'll likely need to use an external mosfet switch. I could go synchronous if I can find a compatible controller IC.

    Here's the features I'd like.

    -Synchronous operation
    -Low voltage shutdown when VCC < ~10v
    -Feedback input for voltage regulation
    -Current limiting/regulation (optional)
    -Programmable soft-start
    -Some way to enable the controller with a low current signal. I can pull down the softstart capacitor if softstart input begins at >0.6v (so a pnp transistor can hold it low)
     
    Last edited:
    lazzer408

    lazzer408

    Member
    2010-09-12 1:44 am
    Chicago
  • #5
    Here's a better idea of what I need. Pin locations do not matter. Has anyone seen an IC like this? The bootstrap capacitor should be connected to Q1 source but you get the idea.

    attachment.php
     

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    whizgeek

    Member
    2010-02-16 11:47 pm
  • #6
    Isn't bootstrapping only needed to drive a high side mosfet where the output is higher than the drive voltage?
    You don't need it here. 14V is more than enough to drive outputs in your case.

    Why not use the IC you linked, with a external transistor, as per datasheet?
     
    lazzer408

    lazzer408

    Member
    2010-09-12 1:44 am
    Chicago
  • #7
    whizgeek said:
    Isn't bootstrapping only needed to drive a high side mosfet where the output is higher than the drive voltage?
    You don't need it here. 14V is more than enough to drive outputs in your case.

    Why not use the IC you linked, with a external transistor, as per datasheet?
    Click to expand...

    Source pin on the high side mosfet will be whatever Vcc is when it's turned on. Input ranges from 10-14v.

    The IC shows a transistor. I'd like to use a mosfet for efficiency sake. Even the integrated buck controllers (power device and control circuitry in one package) use a bootstrap cap if the controller contains a mosfet switch.
     
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