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LM5170EVM-BIDIR: LM5170EVM-BIDIR: Using as a buck-boost

Kasun Rathnapala
Prodigy 230 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170, LM5170-Q1, LM5176-Q1

Hi,

I recently bought LM5170EVM-BIDIR to check that if i can use it implement a battery to battery charger. Required charging currents are 30A and 45A. Is it possible to use this devkit as a buck-boost. Where I can get 14.5V as the output if the input voltage varies between 8V and 16V?

Additionally how can I control the output current? 

  • 0
    TI__Guru* 78070 points

    Hi Kasun,

    Thank you for reaching out.  The EVM can only operate buck in one direction and boost in the other direction.  Do your two batteries must share a common ground or they are two independent batteries?  I just want to see if an inverting buck-boost can be used, in which the two batteries do not share the same ground.  

    If they are have to share the same ground, then you may consider to use cascade LM5170, as shown in the attached drawing.  In this way, you just need a create an intermediate rail, say 24V.   The drawing works for bi-directional.  If you  just want unidirectional, simple set DIR to boost for the left converter, and the buck fo th eright converter.  Control ISETA to control the output current.

    Thanks,

    Youhao Xi, Applications EngineeringLM5170 for Buck-and-Boost bidir.pdf

  • 0 in reply to Youhao Xi
    Prodigy 230 points

    Hi Youhao,

    Thanks for your quick response. My application is charging a led acid battery. Source can be the main battery or the alternator. So both batteries share the same ground and 12v (14.5) rail. According to the info I found I this forum, I might need to use two chips, first will boost and other will buck to 14.5. Am I correct?

    Or do you have any other solutions for my application which supports higher charging currents?

    Thanks.

  • 0 in reply to Kasun Rathnapala
    TI__Guru* 78070 points

    Hi  Kasun,

    If you just need unidirectional, you can consider the Lm5176-Q1 four switch buck-boost to charge the battery.  For bidirectional, the previously mentioned topology (boost-up then buck-down, for both directions with the LM5170-Q1) is my recommendation.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 230 points

    HI Youhao,

    Thanks for your suggestions.