Electronics > Projects, Designs, and Technical Stuff
Problem with BQ29700 battery protection IC [SOLVED]
Unixon:
Daixiwen, thanks for such a detailed reply. I'll check for these particular issues.
I didn't get my hands around to do all required testing yet, just confirmed the problem with a lesser circuit.
--- Quote from: Daixiwen on August 02, 2019, 08:07:35 am ---I don't really know what the pull downs would be for.
--- End quote ---
The datasheet says they are for discharging MOSFET gates.
My suspicion is that they may have side effects on state transitions because they are referenced to different grounds.
--- Quote from: Daixiwen on August 02, 2019, 08:07:35 am ---By the way is it truly a BQ29700, or another one in the BQ297xx family with different thresholds?
--- End quote ---
No, I have only *00 parts. I might need *01-*03 if *00 OCD level will be too low for a particular load, but I don't have them at the moment.
--- Quote from: Daixiwen on August 02, 2019, 08:07:35 am ---If you are suspecting the BQ29700, contact your local FAE, they can be helpful in finding the causes and have access to information and contacts at TI.
--- End quote ---
Currently I suspect myself of not understanding something very basic about this IC.
However, I'm thinking of getting other ICs - another batch of 29700, mods 01-07 of it, alternative ICs like S8261 and DW01A.
I don't know... the circuit is so simple that there's just no place to be wrong. And yet something is wrong.
Daixiwen:
I tend to avoid TI battery management chips because there are often gotchas in the specs that make them hard to use. But I agree that for a one cell protection IC there isn't a lot that can go wrong.
The S8261 is a good choice. Very robust. About 15 years ago we had a battery with several of them and our customer wanted us to run a RS105 test on it (EMP pulse, 50 kV/m). The circuit was unshielded and I was sure the test would fry everything, but the Seiko chips worked fine during and after the test.... indestructible!
I'm more familiar with the S8261 than the BQ29700 but the principle should be the same.
Unixon:
Finally the problem has been solved after trying almost all available alternatives.
Some of boards for BQ29700 failed due to poorly soldered QFN MOSFETs and were fixed by resoldering them after manually tinning pins, some other were fixed by replacing the protection IC itself. These boards were a small upgrade and they were designed straight for production without additional test points which made it difficult to understand what's even happening.
So, although BQ29700 boards are now up and running, eventually we decided against TI's part for two main reasons:
1) Unique package and pinout, incompatible with alternative ICs, low availability of ICs with different overcurrent detection thresholds;
2) BQ29700 starts in locked state and requires manual resetting which makes bad first experience for customers;
Other protection ICs DW01A/S8261/AP9101 all share the same SOT23-6 package and pinout plus many more options available in terms of timings and thresholds.
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