BQ76952: Current limiter circuit

Hello Oussama,

Yes, you should be able to use the TIDA-010208 . You can share your final schematics with us if you want us to double check it.

For current limiter, do you mean a pre-discharge type of circuit To avoid inrush currents on initial start-up? The BQ76952 has an integrated high-side P-FET pre-discharge and pre-charge drivers, which are used to limit the current of initial charge/discharge currents.

Best Regards,

Luis Hernandez Salomon

Oussama_BMS.pdf

Hello Salomon,

Thank you for helping me; I appreciate your assistance.

I have attached my schematics and a similar BMS from the market. I understand that they use two coils and some chemical capacitors with 220 µF and 100 V. My goal is for my BMS to safely handle the high current from the 16 LFP batteries.

Could you please review my schematics and provide any recommendations to ensure safety and reliability with the high current?

Thank you for your support.

Hello Oussama,

To safely handle high currents, you would have to design your board to do so, you would need your sense resistors and MOSFETs to handle the current.

You seem to have already many FETs in parallel. I see you have two 2-mOhm sense resistors, will these be able to handle your current?

As for additional comments on the schematic:

• I'd suggest to add footprints for 0.1-uF capacitors on the SRP/SRN pins to Vss, just in case additional filtering is required.
• R21 should be 20-Ohms for best accuracy on cell 16 during cell balancing
• I'd suggest to make D38/D27 as do-not-place (DNP/DNI)
  • Only add if needed.

Besides that, I think all looks good!

Best Regards,

Luis Hernandez Salomon

Hello Salomon,

Thank you for your reply. Your assistance is very helpful, and I appreciate your time.

I wanted to confirm my calculation for the voltage drop of 50 mV (0.05 V) at 100 A:

R= 0.05V / 100 A = 0.0005 ohm

This means I would need a shunt resistor with a value of 0.5 milliohms (0.0005 ohms).

Power Rating of the Shunt Resistor:

P= 0.05 V*100² A = 5 W

• Shunt Resistor Value: 0.5 milliohms (0.0005 ohms)
• Power Rating: 5 W

Additionally, I have added a 0.1 µF capacitor to the ground on both SRN and SRP for filtering as shown in the capture bellow, which I believe is a good idea.

I have a question regarding the number of parallel FETs needed to handle the current accurately. How can I determine this?

Best regards, 

Oussama.D

Hello Salomon,

I hope you're doing well.

Could you please provide guidance on selecting an inrush current limiter or advise recommendation for a parallel battery pack setup (parallel BMS)?

Thank you and have a great day.

Best regards,
Oussama D.

Hello Oussama,

When paralleling BMS, you must ensure that the battery stack voltage is similar between the battery packs, otherwise there may be a high inrush current between the packs. Ideal diodes may be needed to control when the battery stacks are first connected.

For a current limiting circuit, we have the pre-charge/pre-discharge FETs, which are really meant to control inrush currents due to capacitive loads, or to slowly charge the battery if needed.

Best Regards,

Luis Hernandez Salomon

Hello Salomon,

Thank you for your prompt response. I would appreciate it if you could review the precharge section of my schematics to ensure everything is in order.

Thank you for your assistance.

I wish you a great day.

Best regards,

Oussama DallaliFET CHARGE AND DISCHARGE.pdf

FET CHARGE AND DISCHARGE.pdf

Hello Salomon,

Thank you for your feedback. I've made all the changes you suggested, including adjusting the resistor values and marking the Zener diodes as DNI/DNP.

However, I’m a bit unclear about your last point regarding the PCHG/PDSG pins. Could you please clarify the exact connection you’re recommending for these pins in relation to Q51/Q20's gate node?

Thank you for your guidance.

Best Regards,

Oussama

2605.FET CHARGE AND DISCHARGE.pdf

Hello Salomon,

Thank you for your support and assistance. Your guidance has been extremely helpful to me. Please accept my sincere respect.

Best regards,
Oussama