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TPS50601A-SP: Reverse Current Mode

Part Number: TPS50601A-SP
Other Parts Discussed in Thread: TPS7H4001-SP

Tool/software:

Hello E2E,

    These questions apply to a critical long duration space-flight mission:

  • As compared to running the TPS50601A-SP in continuous forward conduction mode are there any detrimental impacts to running it in reverse current/discontinuous mode on: Ripple/Noise voltage, Transient response, regulation, etc.
  • Does the PSPICE transient model include accurate behavior of the TPS50601A-SP when operating in reverse/discontinuous mode.
  • Is it advisable to keep TPS50601A-SP designs operating in continuous forward conduction mode or is the part designed for comparable performance in reverse-current/discontinuous mode as compared to continuous-forward-conduction mode?
  • Is there an efficiency versus switching frequency curve available, couldn’t find it in the datasheet? Typically more efficient to run at lower frequency but that can exacerbate reverse current.

 

For context:

We’ve analyzed our VRM’s for maximum current loads and are now double-checking designs at minimum current loads.   Not unexpectedly at very low load currents it’s possible the inductor ripple current can reverse, e.g. (Inductor Ripple Current)/2 > (Load Current).  Doing some extreme what-ifs to help understand how the part is behaving we see inductor current reverse, go to zero, and the PH Node go up to Vin+0.5V, indicating the reverse current might be flowing back thru the high-side FET.   Occurred to us we need to ask you folks if there’s any detrimental impacts of operating the part in reverse/discontinuous current mode, and if yes what those impacts are.

Thank you,

-John

  • Hi John,

    What you seem to be describing is the expected operation of synchronous buck converters (forced CCM). This is expected operation for the TPS50601A-SP and the device has been tested with this in mind.

    The PSPICE model should represent the device over its full output current range.

    Thanks,

    Andy

  • Thanks Andy,

      So the part has been designed to force ccm when current goes negative, and no detrimental impacts are expected during forced ccm including no degradation in reliability, correct ?

    Also, is there an efficiency versus switching frequency curve available ?

  • John,

    Yes, at low currents where one would normally expect DCM operation, the device is designed to let the inductor current go negative to force CCM operation.

    Unfortunately, this particular device seems to only have an available efficiency plot for one switching frequency. If you are just looking for an idea of how switching frequency generally effects efficiency, some of our newer synchronous buck converters, like the TPS7H4001-SP, have multiple efficiency plots across VIN, VOUT, IOUT, and switching frequency (TPS7H4001-SP Efficiency Plots). Of course, this is a different device, so the efficiency plots from the TPS7H4001-SP will not be directly applicable to the TPS50601A-SP.

    Thanks,

    Andy

  • Thanks Andy, we'll proceed accordingly -John