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BQ25180: NTC connection when used with fuel gauge

Steve Fenwick1
Prodigy 250 points
Part Number: BQ25180
Other Parts Discussed in Thread: BQ27220

We're using a BQ25180 with a BQ27220 fuel gauge. The pack has one NTC and an internal PCM to manage out-of-spec conditions.

To which device should the NTC be connected? Normally I'd connect it to the charger to protect against charging the pack at over or undertemp. But since the pack has a PCM that (I believe) manages over and undertemp, should it connect to BIN on the BQ27220 to improve gauging accuracy?

So, two questions:

1) If the PCM protects the pack against over/undertemp, where should the NTC connect?

2) If the PCM doesn't protect (sufficiently) against over/undertemp, where should the NTC connect?

Thanks!
Steve

  • 0
    TI__Mastermind 23410 points

    Hi Steve,

    I don't see anything about regulating the charge current based on battery temperature on the BQ27220. If you're not looking for this (which the BQ25180 does) feature where the charge current / charge voltage adjusts based on the battery temperature, then you can connect it to the BQ27220.

    Otherwise, you cwant to connect it to the BQ25180 which will adjust charge current based on battery temperature.

    If the PCM can protect the pack in a similar way (such as JEITA or HOT/COLD disable) then we can connect it to the BQ27220.

    If in software, you're able to read the temeprature of the battery from the BQ27220 more accurately and reduce the charge current and charge voltage, then connecting to the BQ27220 is fine. 

  • 0
    TI__Mastermind 20570 points

    Hi Steve,

    Would you please clarify what PCM is? Do you mean the internal protection board? 

    The BQ27220 has internal temp sensor which can be use to sense battery temp. Therefore, you can connect the NTC to the BQ25180 for specific charging profile such as JEITA for battery temperature monitoring regardless of the PCM under/over temp protection.

  • 0 in reply to Jing Zou
    Prodigy 250 points

    PCM: Yes, the OVP/UVP/OC protection on the pack. The charger is at least a few inches from the pack so using the charger's temp sensor may be problematic. But better to have the NTC on the charger than on the fuel gauge; sager. Thanks!