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Mosfet driver requires low esr, esl capacitor. Any suggestions on what to use? — Parallax Forums

Mosfet driver requires low esr, esl capacitor. Any suggestions on what to use?

ElectricAyeElectricAye Posts: 4,561
edited 2012-09-03 00:09 in General Discussion
I'm planning on using a mosfet driver and the data sheet says this on page 5:

There should be a low ESR, low ESL capacitor of 0.1 μF between VDD (pin 8) and PGND and a separate 0.1-μF capacitor between VDD (pin 1) and AGND.

http://www.ti.com/lit/ds/symlink/ucc27321.pdf

Any suggestions on exactly what (Digikey?) capacitor to use? How low is low enough when it comes to ESR and ESL? I plan on using this thing to make pulses with a width of about 10 usec but the pulses happen at only about 400 Hz.

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-08-31 21:33
    A surface-mount (for the low ESL) ceramic (for the low ESR) cap should work okay.

    -Phil
  • ElectricAyeElectricAye Posts: 4,561
    edited 2012-08-31 21:43
    Phil Pilgrim (PhiPi) wrote: »
    A surface-mount (for the low ESL) ceramic (for the low ESR) cap should work okay.

    -Phil

    Wow, Phil, thanks for the super fast reply! My impression is that I'm supposed to use only one 0.1 uF cap, not two, between each Vdd and ground. So is it okay to use just a single ceramic cap for each of those points?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-08-31 21:48
    See page 9 of the datasheet. In addition to the 0.1uF caps (one per each ground), they recommend an additional "relatively low ESR" 1uF cap between Vdd and ground. This can also be a surface-mount ceramic cap. So three caps total.

    -Phil
  • ElectricAyeElectricAye Posts: 4,561
    edited 2012-08-31 21:55
    Phil Pilgrim (PhiPi) wrote: »
    See page 9 of the datasheet. In addition to the 0.1uF caps (one per each ground), they recommend an additional "relatively low ESR" 1uF cap between Vdd and ground. This can also be a surface-mount ceramic cap. So three caps total.

    -Phil

    Amazing. Thank you! Now I just need to find a surface mount cap physically large enough I can actually solder. :-)
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2012-09-01 05:58
    Hi ElectricAye;

    Dito to Phil to keep the Driver happy.

    Just to add, keep the trace lengths short and fat.

    Make provision for a series resister to the MOSFET gate.
    This is commonly in the 5 to 50 Ohm range.
    Often used to reduce ringing and radiated noise to keep the other components in the micro happy.

    Also, take a look at the International Rectifier products.
    They were the pioneers in this class, and possibly cheaper too.

    Duane J
  • ElectricAyeElectricAye Posts: 4,561
    edited 2012-09-01 07:46
    Duane C. Johnson wrote: »
    ...

    Make provision for a series resister to the MOSFET gate.
    This is commonly in the 5 to 50 Ohm range....to reduce ringing...
    Also, take a look at the International Rectifier products....

    Will do, Duane, thanks for the tips!
  • max72max72 Posts: 1,155
    edited 2012-09-02 13:49
    I use 0805 smt caps and in my opinion they are a nice form factor, small but still easy to solder.
    If you want to test them and you can get some you could use a perfo board or a veroboard. The pads spacing fits well this size.
    After that you can decide if they are ok or too small.
    Massimo
  • ElectricAyeElectricAye Posts: 4,561
    edited 2012-09-02 19:01
    max72 wrote: »
    I use 0805 smt caps and in my opinion they are a nice form factor, small but still easy to solder....

    Thanks, Massimo.
  • max72max72 Posts: 1,155
    edited 2012-09-03 00:09
    A similar discussion in the past:
    http://forums.parallax.com/showthread.php?141701-SMD-Capacitor-Type
    Check post #6, Phil describes very well the soldering approach, and along the discussion a comparison between 0805 and 0603 is made.
    Massimo
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