Using LTC4015 along with BMS ( Battery Management System)

Hello,

So you plan to use the LTC4015 for its coulomb counter alone? If the BMS is going to handle the charging, I do believe the LTC4015's own charging algorithm will interfere. It sounds like you may just want to use a standalone coulomb counter that is not integrated into a battery charger.

Perhaps you chose LTC4015 because most of our coulomb counters will not handle your voltage range, but we do have one that will:

https://www.analog.com/media/en/technical-documentation/data-sheets/2944fa.pdf

Regards,

Zack

Thank you . 

Lastly, is it convenient to test the complete designed circuit on perfboard before designing PCB .

The reason being that LTC2944 datasheet have PC Board Layout considerations so manual soldering might be unsafe on perfboard.

Thank you.   

Hello,

It would be very difficult to solder directly to a perfboard without the correct footprint. You could use a breakout board for this package instead:

https://www.icbreakout.com/collections/breakout-boards/products/dfn-8-breakout-board-3x3-mm-0-65-mm

And then mount that onto the perfboard.

Follow the PCB considerations as best you can on this prototyping board, but for this particular part I think you can get away with a little bit.

Generally you would use a heat gun to mount these DFN packages, but the exposed pad on the bottom does not connect to anything in this case, so you might be ok with a standard fine-tip soldering iron.

Regards,

Zack

thanks!

In datasheet, there is no information about choosing sense resistor. But in Dev. board they mentioned 1206 as per needs. Do you suggest any specific for current upto 30+ amps?

Hello,

Not really. Just make sure it is the right resistance value and has a power rating to handle the max current through it with some margin.

Regards,

Zack

Understood. In the Datasheet (LTC2944), Page 11 says that sense resistor is chosen bearing in mind the max. capacity of battery used and so the registers C,D for QBat storage.. Here my capacity is 30Ah. So as per equation @ Page11, I'm getting sense resistor value to be 37 uohm. Is my working fine or I overdid my calculation?

Thanks.

Hello,

I'm getting (0.340 * 65,536 / 30,000) * 50mOhms = 37mOhms instead. That's the equation you're looking at, right? Double-check that?

Regards,

Zack

Zack it is ( ( ( 0.340 * 10^-3) * 65536 ) / 30,000 )* 50mOhms = 37 uOhms. Using this small resistor might decrease the counter efficiency since Vsense will be very low. 

Hello,

The 0.340 is in mAh already and your capacity was 30Ah, so if you multiply the 0.340 by 10^-3 to convert mAh to Ah then you should just divide by 30 (Ah) instead of 30,000 (mAh). So either way that would yield 37mOhms.

Regards,

Zack

Yes Zack, you're correct. Thank you again.

Hence I conclude that using :

1.  RSENSE ≤ (50mV / Imax) , I get RSENSE ≤  1.56 mOhms  ( IMAX = 32 A)

2. RSENSE ≤ ( 0.340mAh• 2^16 •  50mΩ )/ QBAT ( For  IMAX = 32 A and Battery Capacity = 30 Ah )                      I get RSENSE ≤ 37.13 mOhms 

Thus, using both equations 1 and 2, RSENSE for my application is 1.5 mOhms 

Yes Zack, you're correct. Thank you again.

Hence I conclude that using :

1.  RSENSE ≤ (50mV / Imax) , I get RSENSE ≤  1.56 mOhms  ( IMAX = 32 A)

2. RSENSE ≤ ( 0.340mAh• 2^16 •  50mΩ )/ QBAT ( For  IMAX = 32 A and Battery Capacity = 30 Ah )                      I get RSENSE ≤ 37.13 mOhms 

Thus, using both equations 1 and 2, RSENSE for my application is 1.5 mOhms