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Parallel TPS27081A

RMauser
Prodigy 30 points

Other Parts Discussed in Thread: TPS27081A, TPS27082L

Hello, I currently have one TPS27081A as a high-side switch and it tends to overheat at higher loads (2amps+). I was thinking about putting two of them in parallel to improve power handling and was curious what value gate resistors I should put on them when being driven from the same microcontroller's enable pin.

Also, can the two mosfets share the same 10k pull-up resistor? Thanks for any help!

  • 0
    TI__Guru**** 174616 points

    RMauser,

    To match the rise times, it would be good to parallel every pin of the two TPS27081A. There would be just one R1, R2, and C1 passive component. Good layout should ensure good current sharing.

  • 0 in reply to Ron Michallick
    TI__Prodigy 580 points

    Is this for an automotive application?

    David

  • 0 in reply to DavidT
    Prodigy 30 points

    Hello! Yes this is for an automotive application - it is switching 5V that has already been stepped down from the car battery by a separate DC buck converter. I have a microcontroller/GPIO logic controlling the TPS27081. Is there a better load switch available for 3amps 5V with logic-level control? Thanks for your input!

    If I do parallel two of the TPS27081 - in my existing single switch design I haven't been setting the slew rate so there is no R2 or capacitor. Would I need to consider adding those components when paralleling?

  • 0 in reply to RMauser
    TI__Guru**** 174616 points

    RMauser,

    No, you do not need to add the extra components.

  • 0 in reply to Ron Michallick
    Prodigy 30 points

    Thank you for your help! Just to verify- I shouldn't need individual series gate resistors on the on/off pins when paralleling them. Just add an additional TPS27081 and share the R1 pull-up resistor, and parallel all the other pins?

  • 0 in reply to RMauser
    TI__Guru**** 174616 points

    RM,

    Yes that is correct.

  • 0 in reply to Ron Michallick
    Expert 2180 points

    Ron,

    I cannot understand this: if we parallel the pins of two TPS27081A but share external resistors and capacitors, doesn't this change the effective R and C and consequently the rise/fall speed?

     

    Matt

  • 0 in reply to Matt Shira
    TI__Expert 5275 points

    Hi Matt,

     

    This should not change the rise/fall time for the TPS27081A version.  These passive components aren't used to 'program' the device.  The rise time is primarily determined by how quickly the input (VIN) charges the Output Capacitance (C1) - fairly straight forward. 

    The other rise time factor is how quickly the FET turns on and its ON resistance (as determined by VGS).  The VGS is a voltage divider between R1 and R2, so the VGS term is factored out of the final equation.  For the TPS27081A, using the same R1 and R2 in a parallel configuration would result in the same VGS as a stand-alone situation.  Since the VIN and C1 would also be the same, there will be no difference in timing.

    The TPS27082L version would see a difference in behavior since the R2 is integrated as Rs.  In this case, the Rs resistors would be in parallel, resulting in an R2 value equal to 1/2*Rs (12.5kohm).   You should be able to use the equations from the A version to find the expected timing since the L version equations assume 12.5kohm.

    Let me know if this makes more sense!

     

    Best Regards,

    Adam Hoover

    Load Switch Applications Engineer

  • 0 in reply to Adam Hoover
    Expert 2180 points

    Dear Adam,

    Thanks for help!

    I copied additional question to dv/dt for TPS27082L?, could you please answer them there?

     

    Matt