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TPS5450: Circuit changes to support long output cable?

John M
Expert 2135 points
Other Parts Discussed in Thread: TPS5450

We're hoping to use a TPS5450 at 4A-5A (continuous) to supply power to various loads consisting primarily of small incandescent bulbs, switching battery chargers, and LED drivers (for task lighting).

The cable length from the TPS5450 to the load can be as long asy 4 feet (8ft. round trip). Are there any changes you'd recommend making to our SwitcherPro-generated designs to make sure the output remains stable? If necessary, I'll trade some transient response for stability as most of the loads don't change after the load is connected, or the load changes slowly. Unless the input ripple to something like a DC-DC battery charger located 4ft away requires good transient response.

  • 0
    TI__Guru**** 191445 points

    The TPS5450 is an internally compensated device.  Your input voltage, output voltage and current will constrain the output filter as selected by switcherpro.  So your performance will be predetermined.  You will of course have to deal with the losses on your cable, but in general, that should not cause issues.  If you need to change the output capacitor amount or type, use this procedure.

    http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slva237c&fileType=pdf

    Also be aware that the TPS5450 is operating at the thermal performance limit for that package type.  Pay close attention to the pcb layout and thermal relief.

  • 0 in reply to JohnTucker
    Expert 2135 points

    Thanks for the reply!

    The DC losses in the cable won't be a problem for us, just any possible bad effects of the added inductance. We'll stick with the SwitcherPro circuit then (along with 0.1uF MLCC's  added to the input and outputs). I reviewed SLVA237 earlier and while using standard elect. or ceramic caps was an attractive idea, the Nichicon PS and PA Series NPCAP polymers are affordable and SwitcherPro was able to give us a nice solution using them.

    The heating concerned us too so we've dedicated over 4 sq. of 4-layer, 2oz. Cu, PCB for the circuit along with a bit of fan cooling. We're using the EVM layout and will pay close attention to the thermal aspects, including thermal vias to the other layers, etc. Hopefully that's enough. Thanks for the tips!

    I was concerned about the possible downside of using an internally compensated chip (something I originally liked though) but if an externally-compensated chip won't offer any real advantage for an application with long cable lengths to the load, we'll stick with the TPS5450.