BQ28Z610: New to battery systems. Need help

Eduardo Barcellos

Part Number: BQ28Z610
Other Parts Discussed in Thread: BQ25883, BQ40Z60, , BQ34Z100-G1

Hello,

This is my 1st time designing a circuit that incorporates a Li-Ion battery, and I need some help.

The circuit I'm designing needs only 3.3V. And so, I thought of 2s 18650 Li-Ion batteries feeding a switching regulator. The circuit has an LCD display, and it should show the battery charge percentage (State of Charge / fuel gauge) on its top-right corner. And the circuit will have a 5V power input connector, from where it will get power to run if connected and also from where it'll get power to charge the battery. If there's no 5V on the power input connector, the circuit should then get its power from the battery.

So, after studying TI solutions, I thought of using the BQ28Z610 (Battery fuel gauge with integrated protector for 1-2 series packs) to get State of Charge of the battery, and the BQ25883 (2-Cell, 2-A Boost-Mode Battery Charger With Power Path, USB On-The-Go Boost (OTG) For USB Input) for charging the battery.

1st question: Are those good choices for my needs?

I tried to find a 1-chip solution, and found the BQ40Z60 (Programmable Battery Management Unit), but it costs $15 USD on Digikey, and require a large amount of external components.

over 4 years ago

0 Nick Brylski over 4 years ago

TI__Mastermind 19195 points

Hi Eduardo,

BQ28z610 is a good choice here, note that we have an updated version available: bq28z610-r1. One thing to consider is that this is a pack side gauge meaning it it meant to go inside the battery pack (vs a system side gauge that sits with the rest of PCB.)

If you don't have any more questions about gauge I can move this post to the charger team for their comment.

Best regards,

0 Eduardo Barcellos over 4 years ago in reply to Nick Brylski

Intellectual 420 points

Hi Nick,

Thanks for your reply. If the BQ28Z610 is a pack side gauge, what would be the ideal system side gauge for me to use on my system together with the BQ25883 charger?

Thanks,

Eduardo

0 Nick Brylski over 4 years ago in reply to Eduardo Barcellos

TI__Mastermind 19195 points

Hi Eduardo,

Bq34z100-g1 or bq40z60 would fit for system side. You can expect better gauging performance from the pack side as the gauge is always tied to the battery from the very beginning.

Best regards,

0 Eduardo Barcellos over 4 years ago in reply to Nick Brylski

Intellectual 420 points

Hi Nick,

Question 1: As you mentioned the better gauging performance from the pack side, should I then keep the BQ28Z610 IC for my system, but only upgrading to the newer BQ28Z610 -R1? I indeed would prefer to keep it, as I understand most of it already.

Question 2: Is this (on the circuit that follows) pretty much all I gotta do on the fuel gauge side? I'll have 2x 18650 Li-Ion cells, 3.7V or 4.3V each.

Question 3: I understand the function of all FETs on the circuit above except Q5 (bottom right) and the 15V zener diode on it. What are their functions?

Thanks again,

Eduardo

0 Ricardo over 4 years ago in reply to Eduardo Barcellos

TI__Genius 10385 points

Eduardo,

In addition to Nick's comments, please have a look at this reference design:

It is very similar to your application and may provide some clarity.

Best Regards,

Ricardo

0 Eduardo Barcellos over 4 years ago in reply to Ricardo

Intellectual 420 points

Thanks Ricardo,

That's actually where I took that circuit from. I just don't understand the reason for Q5 and D10 (the FET & zener diode on the bottom right). What are their functions? Are they really necessary?

Thanks again,

Eduardo

0 Ricardo over 4 years ago in reply to Eduardo Barcellos

TI__Genius 10385 points

Eduardo,

The NMOS and Zener diode serve as a reverse polarity protection circuit. If you plan on using discrete cells that can be removed and inserted in the wrong polarity, then this circuitry is essential.

Best Regards,

Ricardo

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BQ28Z610: New to battery systems. Need help