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LM5170EVM-BIDIR: how to calculate the maximum load current when HV = 48V, and LV = 20V

cheng zhang10
Prodigy 40 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170-Q1, LM5170

Hi, 

I am using a LM5170-Q1 EVM, to control the bidirectional power flow between two battery packs. The high voltage (HV) side is 48V, and the low voltage (LV) side 20V. 

I am not sure how to determine the maximum load current at the LV side? and what are the limiting factors for this maximum current? 

I learned from the use guide that the maximum power is around 700W when HV = 48V and LV = 12V. Does this power limit apply to different HV and LV combinations?  

Many thanks. 

  • 0
    TI__Guru 68725 points
    There is not a hard limit for the max current. It is a tradeoff between the efficiency (thermal related) and maximum, load. The driver is 4A/5A strong and it can drive parallel MOSFETs to share the current. However, too many FETs in parallel may have more switching losses.

    Another limiting factor is current capability of available inductor. See what you can use. The EVM is limited to 700W because of the selected inductor can only handle ~32A, not because of the LM5170 power capability. Just an reference for you: we have customers doing >600W per phase.
  • 0 in reply to Youhao Xi
    Prodigy 40 points

    Dear Youhao, 

    Many thanks for your reply. 

    I have another question. The LM5170-Q1 EVM provides that the maximum voltage for low voltage (LV) side can reach 60V. If the LV side maximum current is 30A imposed by the inductor, does this mean the board can deliver power up to 60V x 30A = 1800W, or just for transient peak power? 

    In my application, if I set the LV side = 30V, and LV side current = 30A, will this pose any danger to the board? 

    Many thanks. 

    Regards

    Cheng

     

  • 0 in reply to cheng zhang10
    TI__Guru 68725 points
    No danger but you need to adjust the OVPB on the EVM to allow 30V operation in Buck mode. I remember the EVM sets OVPB at about ~20V.