BQ25750: what do I have to consider, when I have a system which can draw 75A Max current?

Hello Silvan,

The BQ25750 has power path switchover limit of 8A so the BQ25750's default power path will not work for this situation. For a system current of 75A, I recommend using a dedicated hot-swap controller or E-Fuse like the TPS4800-Q1. You can ask the hot swap controller experts for more questions about this.

Do you have an MCU in your application? If you have an MCU, you can use the BQ25756 to charge the batteries and the MCU can control the power path.

Here's the FAQ on the BQ25750's power path switchover by the way. Just for reference, here's the BQ2575X family FAQ page.

Let me know if you have any questions about this or if you have any questions about the set up.

Best Regards,
Ethan Galloway

Hello Ethan

Do you have any schematic or idea on how I need to design this TPS4800-Q1 chip into my system? (how to design it with my BQ25750 so it will work right)

EDIT: I just read this on the FAQ on the BQ25750's power path switchover: 

1. To disable the protection on the BATFETs, you can connect the BATFETs from the system to the SRN side of the sense resistor instead of from the system to the SRP side of the sense resistor. Keep in mind, the IC will no longer be able to monitor the current into the system because the system current no longer flows through the battery current sense resistor.
   
   
2. To disable the protection on the ACFETs, you can short across the AC sense resistor. With this setup, the IC will no longer be able to monitor the input current and the IAC_DPM will no longer work.

     If the protection on the ACFETs/BATFETs is disabled, damage can occur to the ACFETs/BATFETs from the in-rush current spike. You will need to make sure the FETs are sized appropriately and have a high SOA to handle the current of your application 

-> does this mean I can use the BQ25750 but just without any AC and BAT side current monitoring? Either way, I would have set the current limits to MAX. or as high as possible (because I knew I have high current system) so would this work? 

I think all the other features with voltage monitoring etc. would still work in correct way right?

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What would happen, if I would take the BQ25756 IC chip, which has no power path, would it then working? I think when I design all the MOSFETS, traces etc. for 75A shouldn't it work then? -> So it will only be a battery charger. Because I don't think i really need a power path control, it was said to me, that you can have a load attached on the battery pack and still being able to charge the battery up. Or what do you think?

Thanks

Silvan 

Hello Silvan,

Silvan Sommer said:

Do you have any schematic or idea on how I need to design this TPS4800-Q1 chip into my system? (how to design it with my BQ25750 so it will work right)

I made a typo here. The TPS4800-Q1 only has 1 FET and is unidirectional. For bidirectional blocking, you can use the TPS4811-Q1 or the TPS4810-Q1. For the BATFETs, you'll need to tie BATSRC to GND and BATDRV to EN/UVLO pin. For the ACDRV, you'll need to tie this pin to EN/ULVO through a voltage divider.

Silvan Sommer said:

-> does this mean I can use the BQ25750 but just without any AC and BAT side current monitoring? Either way, I would have set the current limits to MAX. or as high as possible (because I knew I have high current system) so would this work? 

You'll still want to have the bat sense resistor to control the charging current. The bat sense resistor just shouldn't have the system load current going through it.

Silvan Sommer said:

I think all the other features with voltage monitoring etc. would still work in correct way right?

Yes, the voltage ADC will work here. Keep in mind, the ADC is intended to provide a general indicator for the voltage and current levels.

Silvan Sommer said:

What would happen, if I would take the BQ25756 IC chip, which has no power path, would it then working? I think when I design all the MOSFETS, traces etc. for 75A shouldn't it work then? -> So it will only be a battery charger. Because I don't think i really need a power path control, it was said to me, that you can have a load attached on the battery pack and still being able to charge the battery up. Or what do you think?

Yes, if the system load is in parallel with the battery, the BQ25756 will work here and you won't need a power path. Keep in mind that the BQ25756's charge current is only 20A. To get more charge current, you can use multiple BQ25756 ICs in parallel.

Let me know if you have any questions about this.

Also, if the power path isn't critical, I'd recommend using the BQ25756 and keeping the load in parallel with the battery. This will be the easiest setup.

Best Regards,
Ethan Galloway

Hello Ethan

Thanks for the answer you are helping very much! :) 

I think I will take the BQ25756 in parallel to increase the charging current. 

Do I need to make a second IC circuit of this BQ25756 (so that I have 2 BQ25756 circuits in parallel) and just connect them in parallel to my battery pack right? or are there also things to consider? 

Should I programm these 2 circuits so each of them has 1/2 of the full current? (when I want to charge with 30A, each of them load with 15A?)

Thanks and have a nice weekend.

Silvan