BQ25756: BQ25756RRVR connections in parallel

Hello Narendra,

narendra singh1 said:

Can BQ25756RRVR be connected in parallel to increase current requirement? If yes, is there any synchronization required?

Yes, the BQ25756 can be connected in parallel to increase the current requirement. The BQ25756 acts as a current source. So, the currents will add in parallel. For synchronization, I recommend connecting an external clock source to the FSW pin of both BQ25756 ICs.

narendra singh1 said:

Will MPPT work in this case when i connect solar panels in series or parallel?

If each BQ25756 is connected to it's own solar panel, MPPT will work in parallel. MPPT will not work when the BQ25756 ICs in parallel have the same input source.

narendra singh1 said:

Is there any part recommendation for Input power protection from Automotive surges/dump/crank etc for this high current and 11-32V wide input

The BQ25756 IC has a maximum rated voltage of 85V. The BQ25756 will be fine from voltage surges. I'm not familiar with input power protection, but maybe you could use the TPS4800-Q1 to protect from over-currents and short circuits? I can loop in the power protection experts to provide more recommendations if you want.

Best Regards,
Ethan Galloway

Hi Ethan,

Thanks for your confirmation on connecting in parallel.

Regarding Solar input, when we connect panels in series and supply this combined voltage as input to BQ2576 connected in parallel, will MPPT be effective?

Regards 

Narendra Singh 

Hi Ethan,

I am just wondering what limits MPPT not to follow while series/parallel combinations. It's very standard practice to connect solar panels in series/parallel connections depending on voltage/current requirement. There are multiple MPPT chargers end products available in market which support 12/24/36/60V solars and i am pretty sure they don't expect to connect in 1S configuration because 12V panels are standard available. They work fine with any combination.

For our application, do you have any other recommendations in which i can connect for example 2S or 2S2P configuration and MPPT should work? I have power requirement of 500 to 600W and hence i want to connect BQ25756  in parallel combination.

Regards

Narendra Singh

Hello Narendra,

Thanks for being patient with this. Let me clarify the BQ25756's MPPT functionality.

MPPT on the BQ25756 works by sweeping the VAC_DPM voltage and finding the maximum charge current from the sweep. This algorithm allows the BQ25756 to find the maximum power point of multiple series or parallel solar panels. The BQ25756's MPPT algorithm will also disregard local maximum points. The MPPT algorithm will also do a full sweep of the panel to relocate the maximum power point at a set time.

Because of the MPPT algorithm, 2 BQ25756 ICs can't work in parallel from the same solar input. Their MPPT algorithms would mess each other up. You might be able to work around this by forcing the BQ25756 ICs to do a full panel sweep at exactly the same time, but we haven't verified this functionality.

Let me know if that makes sense and let me know if you have any questions about this.

For your application, I would recommend using 2 BQ25756 ICs charging the battery in parallel. Each BQ25756s would fed by a separate group of solar panels. I made a quick block diagram of what this would look like:

Let me know if this would work for your application and let me know if you have any questions about this.

Best Regards,
Ethan Galloway

Hi Ethan,

Yes, i am understanding what you are saying. As our power requirement is quite high, does TI have any other recommendations which can accept high input current?

Regards

Narendra Singh

Hello Narendra,

For a higher input power requirement, you might have to go to a more complicated system.

I've attached a few reference designs below that may help:

• https://www.ti.com/tool/TIDA-010949
• https://www.ti.com/tool/TIDA-010042
• I got these links from here:https://www.ti.com/solution/solar-power-optimizer

Best Regards,
Ethan Galloway