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TPS54560: Current sharing with TPS54560

Ricky Thomson
Prodigy 30 points
Part Number: TPS54560
Other Parts Discussed in Thread: TPS5450, UCC39002, TPS54620,

Hi there,

I wanted to check if there is a possible way to parallel 2 TPS5450 to double the total current available to the load?

I've had a read of two similar post that says these devices aren't really designed for this purpose and recommends the UCC39002 http://www.ti.com/product/UCC39002, to regulate the feedback for each device.

However I also stumbled upon this which seems to show the parallel operation of two very similar devices (TPS54620) http://www.ti.com/lit/an/slva389/slva389.pdf , and just wanted to check whats the main difference between these two devices?

Kind Regards

Ricky

  • 0
    TI__Guru**** 191445 points
    Ricky,

    I do not directly support TPS54560, but I mentored the TPSs54620 parallel application project. That particular exercise was conceived as a project for an intern some years ago. While it is technically feasible, that deign was somewhat tricky to produce. The theory behind it is that the output current is directly proportional to the COMP pin voltage, so that if two devices are connected with the outputs combined and the COMP pins tied together, then the output current for each device would be equal. The prototypes we built and tested actually do perform well in this regard, however I think that performance may prove elusive in larger production volumes. Let me explain further. The relation ship between COMP pin voltage and peak switch current is governed by the specification Gmps (COMP to Iswitch gm = 16 A/V in the datasheet Electrical Characteristics table). Gmps governs the rate of change in peak switch current with respect to the change in COMP pin voltage. It does not necessarily determine the absolute value of peak switch current to COMP pin voltage, only the rate of change (or transconductance). So in fact the degree of absolute current sharing may vary by 30% or more due to variations in that parameter. also the COMP pin is extremely noise sensitive. The PCB layout for that application note was somewhat difficult. If I recall correctly (it was nearly 10 years ago), it took more than one attempt to get a working prototype. TPS54560 uses a similar peak current mode control topology, so I would expect the results to be similar.

    Generally I would suggest using a single converter with the appropriate current rating for your application. There are different converters that are specifically designed to be operated in parallel. They will typically be designated as "stackable", or wile have a pin designated as "ISHARE" or similar.

    I hope this may help.