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BOOSTXL-DRV8323RH: Hardware design

Danny Chan
Intellectual 590 points
Part Number: BOOSTXL-DRV8323RH

Hi,

I know this isn't related to TI forum but I really need some help !

I would like to take flat-bed layout approach, however this approach couldn't hold the capacitor in parallel or near VIN, therefore I can only put it away from VIN via wire / thick trace ... 

Is there any problem ? 

Your help is this matter is greatly appreciated

Danny

  • 0
    TI__Mastermind 26416 points

    Hi Danny,

    Is this specifically for bulk capacitance? What capacitor value is being used?

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    Intellectual 590 points

    thank you Anthony,

    It's mainly for braking current handle and high current required by motor.

    If I can locate in that area, I can use 100V 2200uF big capacitor 

    My main question is, if this bulk capacitor is little far away will cause any inductance  ?

    and how about if the BIG CAPACITOR's negative connect to board's GROUND plate ? 

    Danny

  • 0 in reply to Danny Chan
    TI__Mastermind 26416 points

    Hi Danny,

    Having the bulk capacitor farther away will add inductance due to the wires/traces, so it is something to be mindful of. If you decide to connect it farther away, the thicker the traces/wire the less the inductance will be.  Having it as close as possible and connected with thick wires/traces will help reduce inductance. Connecting the negative of the capacitor to the board's ground plane will definitely help.

    Regards,

    Anthony Lodi

  • 0 in reply to Anthony Lodi
    Intellectual 590 points

    thank you Anthony,

    so if I use wire instead of traces, I don't need to worry both length are imbalance ? e.g. GROUND wire longer than VIN connect to capacitor's - and + ?

    Danny

  • 0 in reply to Danny Chan
    TI__Mastermind 26416 points

    Hi Danny,

    Whether you use wires or traces, both will have inductance that you will have to deal with. A trace is essentially a copper wire. The amount of inductance will depend on a few factors:

    1. A longer trace or wire will result in higher inductance

    2. A thinner trace or wire will result in higher inductance

    The thicker the wire, the lower the inductance will be. The wider a trace, the lower the inductance will be. The shorter the wire or trace, the lower the inductance will be. 

    If there is an imbalance of length, you can think of it as one having higher inductance than the other. The main consideration is to reduce the inductance in the current path between the capacitor's VIN and the capacitor's GND. 

    Regards,

    Anthony Lodi

  • 0
    Genius 5040 points
    Danny Chan said:

    I would like to take flat-bed layout approach, however this approach couldn't hold the capacitor in parallel or near VIN, therefore I can only put it away from VIN via wire / thick trace ... 

    Is there any problem ? 

    Hi Danny,

    Solder the cap + as close as possible to FET Drain, and (-) near the FET Source.

    If you use trace or wires, how long are they?

    Brian

  • 0 in reply to Brian Dang
    Intellectual 590 points

    Hi Brian,

    Herewith my PCB layout, if I use Wire instead of Trace 

    for Negative from Mosfet SOURCE to Capacitor which is 56mm + 49mm

    for Positive from Mosfet DRAIN to Capacitor which is 16mm + 27mm 

    If connect Ground plane to Capacitor's negative, the ground plane size is around 51mm x 28mm

    I am little concern if I use Ground Plane connect to Capacitor's negative, can it handle high current ? 

    Danny

  • 0 in reply to Danny Chan
    Intellectual 590 points

    Hi Brian,

    Thanks for you help, got your point it's very important.

    I will re-design my PCB mainly focus on CAPACITOR location.

    Danny