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BQ25858B-Q1: Hotswap and Current Limiting for parallel operations

Vraj Parikh
Prodigy 35 points
Part Number: BQ25858B-Q1
Other Parts Discussed in Thread: LM5066, BQ25856-Q1,

Tool/software:

Hello Ti Experts ,

I need a product recommendation for the following problem statement. 

Two or multiple batteries would be connected in parallel. Lets stick to 2 batteries for starters. Battery 1 and Battery 2 would be in parallel. Vbat min = 41 V and Vbat Max = 57.6V. If both the batteries are at different SoC Levels like Battery 1 is at 80% SoC and Battery 2 is at 20% SoC and if parallel operation is needed, there would be a huge inrush and circulating current since it is an LFP pack, assume per cell resistance of 0.7mOhm and 16 cells are in series which make effective resistance of almost 11.2 mOhm plus the busbar resistance which is still unknown.

For ease of calculation, let battery 1 = 48V and battery 2 = 42V. 

My goal is 
Battery 1 should charge battery 2 to an equilibrium level.
The charging current limit should be limited to 20Amps continuous .
The maximum charging current in worst can be 100 Amps for 500 milli-seconds.
 The charging limits can be configurable.

For majority of the hotswap controllers (Like LM5066) that I researched, the output was a load,but incase the input and output both will be batteries, hence I need some guidance on how to proceed on this.

I understand that there has to be a Firmware Control that checks voltage of 2 battery packs and allows paralleling operation if only the delta is less like 200 - 300 mV, but in this case that is not possible currently.



Thanks and Regards,
Vraj

  • 0
    TI__Expert 6545 points

    Hi Vraj,

    The BQ25856-Q1 might be what you are looking for. The device is a bidirectional battery charger. This only has trickle charge and pre-charge in one direction though. In the reverse direction, it only has CC and CV, so some additional battery protections will have to be added in the host MCU. This may also need to be paired with a hotswap controller.

    The BQ25858B-Q1 might also work. If you have to program the trickle charge and pre charge with the MCU anyway, this device might have more symmetry than the BQ25856-Q1. This is not a battery charger device though, so it only has CC and CV control and no battery protections (such as TS pin).

    Neither of these devices allows for 100 amps. 20 amps is the limit for input and output, and this is configurable with I2C.

    Let me know if this helps answer your question.

    Best,
    Michael