TI E2E Community
Battery Management - Gas Gauge Forum
Selecting the correct BQ27xxx part
Hello, I'm looking for a fuel gauge for a new design. The battery is a LiPo type and I see that many parts in the BQ27xxx family say Li-Ion with no reference to supporting the polymer type. The BQ272xx parts say polymer. In fact there are several out there, but they are all pack side units. What I am searching for is a system side gauge for a removable battery system.
The BQ27500 looks like a perfect part, the BQ27510 specifically since it requires one less part in the system (built in 2.5V LDO). I have two questions about this part.
1. Are the 27500 and 27510 (and 27501 I guess) really unable to accurately monitor Lithium Polymer batteries?
2. Is the 27510 software compatible with the 27500? I have a 27500 EVM and can I transistion to a 27510 on my PCB with nothing more than a parts list change?
All the bq275xx devices will accurately gauge LiFePO4 cells. You need to choose the proper chemistry file from the bqEasy Wizard (located in EVSW software).
The bq27510 has a Low-Iq linear regulator integrated. if you were to do your golden-image cycling with a bq27500, it could seem reasonable to 'port' it over to the '510. However you would need to compare line-by-line the .GG files & update dataflash parameters accordingly. The bq27501 will not be compativel with the bq27500/10. as it has an additional feature of "resistor ID" to switch between profiles.
Best regards, Keith
Thank you for the information Keith. I went ahead and tried my LiPo battery on the 27500 EVM this weekend and seems to work quite well although it still needs a bit of tweaking in the flash settings.
I'd like to ask one more question that I should have included in my original post. I'm wondering if I can directly connect the I2C lines to a CPU limited to 1.8V logic without requiring the added expense of a buffer. I found this link:
It doesn't specifically refer to the BQ275xx family and I would like to be 100% sure that there are no ESD diodes internally or anything that might pull the lines up to 2.5V. Are they purely unprotected open drain pins?
Connecting the I2C lines directly to a CPU is not an issue. However, external ESD protection is required on connectors. There are a few suggestions on ESD in our Impedance Track 'Applications Books' regarding layout & ESD/EMI.
Please note that if you have a continuous pull-up on the I2C lines, then the part won't go to sleep.
Thank you again Keith. Are you sure your comments apply to a system side device as opposed to a pack side device?
For instance, do I still need the extra ESD components for a chip that is inside the device and never get's handled by the user? Does the discharge travel through the sense pins or VBAT to zap the electronics on the I2C side?
Also, since this is a system side device, the pullups will always be there until the system is fully powered down so it is my understanding the using the sleep command or setting the standby threshold current low is how to put this chip to sleep.
If the IC is on system side and I2C is not brought out, you don not need ESD protection. To get into sleep, there has to be no activity on I2C line.
Thank you Ming and Keith.
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