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BQ27542EVM: Fuel Gauge Reporting Zero Average Current and Decreasing Remaining Capacity at Low Temperatures

Hoang Nguyen
Prodigy 10 points
Part Number: BQ27542EVM

Tool/software:

I am using the BQ27542 fuel gauge in my device to monitor a single-cell Li-ion battery. When my device is in a cold state (approximately 0°C) and I plug in a USB charger, I encounter the following issues:

  1. AverageCurrent() Reading 0: Despite the USB charger being plugged in and the device presumably charging, the AverageCurrent() consistently reports 0.
  2. Decreasing Remaining Capacity and Battery Percentage: Instead of increasing, the Remaining Capacity and battery percentage steadily decrease while the charger is connected.

Steps to Reproduce:

  1. Allow the device to reach a cold state (around 0°C).
  2. Plug in the USB charger.
  3. Observe the AverageCurrent(), Remaining Capacity, and battery percentage values.

Questions:

  1. What could be causing the AverageCurrent() to report 0 under these conditions?
  2. Why would the Remaining Capacity and battery percentage decrease when AverageCurrent() to report 0 at low temperatures?
  3. Are there specific configurations or calibrations for the BQ27542 that can mitigate these issues in cold environments?
  4. Could the battery's internal protection mechanisms or increased internal resistance at low temperatures be affecting the fuel gauge's readings?

Additional Information:

  • The fuel gauge configuration has been verified and works correctly at room temperature.
  • The temperature sensor appears to be accurate, reflecting the actual battery pack temperature.
  • The battery and fuel gauge are designed to support the operating temperature range, but these issues only occur at around 0°C.

Any insights or suggestions on how to resolve these issues would be greatly appreciated.

  • 0
    TI__Mastermind 27321 points

    Hello,
    Do you have a log file with more data to see what the gauge reads when you plug in the charger? 

    If remaining capacity is decreasing, the gauge is sensing negative current somehow. Please share your settings to check the Deadband setting. The gauge will not display currents less than Deadband. 

    On another thought, it would be good to check if temperature is affecting the charger or the BMS system in general. Do you have protections in your BMS? Do you have underTemperature protections? Something is blocking the current and it does not necessary have to be the gauge. 

  • 0 in reply to Jose Couso
    Prodigy 10 points

    Fullscreen batteryLog_14_05_2024.txt Download 
    08:18:57 2024/05/14,DISCHG (GOOD),NONE,84,318,4046000,-309000,2349000
08:19:57 2024/05/14,DISCHG (GOOD),NONE,84,318,4075000,-220000,2344000
08:20:57 2024/05/14,CHG (GOOD),WLC,84,319,4160000,475000,2341000
08:21:57 2024/05/14,CHG (GOOD),WLC,84,318,4164000,408000,2344000
08:22:57 2024/05/14,CHG (GOOD),WLC,84,317,4166000,380000,2351000
08:23:57 2024/05/14,CHG (GOOD),WLC,85,315,4167000,361000,2358000
08:24:57 2024/05/14,CHG (GOOD),WLC,85,313,4168000,345000,2364000
08:25:57 2024/05/14,CHG (GOOD),WLC,85,311,4168000,331000,2370000
08:26:57 2024/05/14,CHG (GOOD),WLC,85,309,4169000,318000,2375000
08:27:57 2024/05/14,CHG (GOOD),WLC,85,307,4170000,307000,2381000
08:28:57 2024/05/14,CHG (GOOD),WLC,85,306,4170000,294000,2386000
08:29:57 2024/05/14,CHG (GOOD),WLC,86,304,4171000,284000,2391000
08:30:57 2024/05/14,CHG (GOOD),WLC,86,303,4171000,274000,2396000
08:31:57 2024/05/14,CHG (GOOD),WLC,86,302,4172000,264000,2400000
08:32:57 2024/05/14,DISCHG (GOOD),NONE,86,301,4090000,-364000,2405000
08:33:57 2024/05/14,DISCHG (GOOD),NONE,86,301,4082000,-238000,2405000
08:35:00 2024/05/14,DISCHG (GOOD),NONE,86,301,4124000,-7000,2400000
08:36:02 2024/05/14,DISCHG (GOOD),NONE,86,301,4107000,-157000,2400000
08:37:03 2024/05/14,DISCHG (GOOD),NONE,86,303,4117000,-63000,2401000
08:38:05 2024/05/14,DISCHG (GOOD),NONE,86,297,4122000,-26000,2402000
08:39:08 2024/05/14,DISCHG (GOOD),NONE,86,270,4126000,-7000,2401000
08:40:09 2024/05/14,DISCHG (GOOD),NONE,86,270,4126000,-228000,2401000
08:41:11 2024/05/14,DISCHG (GOOD),NONE,86,251,4105000,-249000,2401000
08:42:13 2024/05/14,DISCHG (GOOD),NONE,86,226,4095000,-59000,2401000
08:43:13 2024/05/14,DISCHG (GOOD),NONE,86,218,4107000,-133000,2400000
08:44:14 2024/05/14,DISCHG (GOOD),NONE,86,206,4096000,-213000,2399000
08:45:15 2024/05/14,DISCHG (GOOD),NONE,86,201,4112000,-58000,2399000
08:46:18 2024/05/14,DISCHG (GOOD),NONE,86,181,4125000,-6000,2396000
08:47:19 2024/05/14,DISCHG (GOOD),NONE,86,180,4106000,-140000,2396000
08:48:21 2024/05/14,DISCHG (GOOD),NONE,86,166,4117000,-52000,2393000
08:49:23 2024/05/14,DISCHG (GOOD),NONE,86,162,4100000,-114000,2392000
08:50:26 2024/05/14,DISCHG (GOOD),NONE,86,145,4126000,-6000,2384000
08:51:27 2024/05/14,DISCHG (GOOD),NONE,86,145,4098000,-6000,2384000
08:52:29 2024/05/14,DISCHG (GOOD),NONE,86,138,4094000,-147000,2380000
08:53:31 2024/05/14,DISCHG (GOOD),NONE,86,126,4118000,-26000,2372000
08:54:34 2024/05/14,DISCHG (GOOD),NONE,86,119,4124000,-6000,2365000
08:55:35 2024/05/14,DISCHG (GOOD),NONE,86,117,4094000,-183000,2365000
08:56:37 2024/05/14,DISCHG (GOOD),NONE,86,111,4093000,-161000,2360000
08:57:40 2024/05/14,DISCHG (GOOD),NONE,85,105,4098000,-161000,2355000
08:58:41 2024/05/14,DISCHG (GOOD),NONE,85,95,4094000,-147000,2344000
08:59:43 2024/05/14,DISCHG (GOOD),NONE,85,94,4089000,-158000,2343000
09:00:45 2024/05/14,DISCHG (GOOD),NONE,85,89,4088000,-164000,2337000
09:01:47 2024/05/14,DISCHG (GOOD),NONE,85,84,4116000,-24000,2331000
09:02:50 2024/05/14,DISCHG (GOOD),NONE,85,76,4120000,-14000,2320000
09:03:51 2024/05/14,DISCHG (GOOD),NONE,85,76,4084000,-199000,2320000
09:04:53 2024/05/14,DISCHG (GOOD),NONE,85,69,4114000,-24000,2310000
09:05:56 2024/05/14,DISCHG (GOOD),NONE,85,66,4123000,-6000,2308000
09:06:57 2024/05/14,DISCHG (GOOD),NONE,85,62,4105000,-66000,2305000
09:07:59 2024/05/14,DISCHG (GOOD),NONE,85,61,4082000,-153000,2304000
09:09:02 2024/05/14,DISCHG (GOOD),NONE,85,61,4082000,-6000,2299000
09:10:04 2024/05/14,DISCHG (GOOD),NONE,85,53,4123000,-6000,2291000
09:11:06 2024/05/14,DISCHG (GOOD),NONE,85,51,4075000,-128000,2289000
09:12:08 2024/05/14,DISCHG (GOOD),NONE,85,49,4075000,-126000,2286000
09:13:10 2024/05/14,DISCHG (GOOD),NONE,85,46,4090000,-98000,2279000
09:14:13 2024/05/14,DISCHG (GOOD),NONE,85,43,4123000,-6000,2277000
09:15:14 2024/05/14,DISCHG (GOOD),NONE,85,41,4083000,-100000,2273000
09:16:14 2024/05/14,DISCHG (GOOD),NONE,85,39,4067000,-112000,2269000
09:17:16 2024/05/14,DISCHG (GOOD),NONE,85,37,4114000,-172000,2265000
09:18:19 2024/05/14,DISCHG (GOOD),NONE,85,35,4030000,-186000,2263000
09:19:20 2024/05/14,DISCHG (GOOD),NONE,85,35,4085000,-155000,2263000
09:20:21 2024/05/14,DISCHG (GOOD),NONE,85,31,4060000,-97000,2255000
09:21:23 2024/05/14,DISCHG (GOOD),NONE,85,30,4054000,-66000,2247000
09:22:23 2024/05/14,DISCHG (GOOD),NONE,85,29,4060000,-136000,2240000
09:23:24 2024/05/14,DISCHG (GOOD),NONE,85,27,4058000,-110000,2238000
09:24:25 2024/05/14,DISCHG (GOOD),NONE,85,26,4061000,-105000,2238000
09:25:27 2024/05/14,DISCHG (GOOD),NONE,85,25,4098000,-26000,2237000
09:26:27 2024/05/14,DISCHG (GOOD),NONE,85,24,4108000,-11000,2233000
09:27:27 2024/05/14,DISCHG (GOOD),NONE,85,23,4063000,-156000,2225000
09:28:27 2024/05/14,DISCHG (GOOD),NONE,85,22,4085000,-49000,2217000
09:29:28 2024/05/14,DISCHG (GOOD),NONE,85,21,4064000,-126000,2215000
09:30:28 2024/05/14,DISCHG (GOOD),NONE,85,20,4052000,-152000,2212000
09:31:29 2024/05/14,DISCHG (GOOD),NONE,84,20,4092000,-26000,2203000
09:32:30 2024/05/14,DISCHG (GOOD),NONE,84,19,4052000,-47000,2193000
09:33:32 2024/05/14,DISCHG (GOOD),NONE,84,18,4058000,-46000,2192000
09:34:32 2024/05/14,DISCHG (GOOD),NONE,84,18,4096000,-47000,2188000
09:35:34 2024/05/14,DISCHG (GOOD),NONE,84,17,4046000,-102000,2180000
09:36:36 2024/05/14,DISCHG (GOOD),NONE,84,16,4102000,-10000,2171000
09:37:38 2024/05/14,DISCHG (GOOD),NONE,84,16,4078000,-105000,2164000
09:38:38 2024/05/14,CHG (COLD),WLC,84,16,4113000,0,2163000
09:39:38 2024/05/14,CHG (COLD),WLC,84,17,4115000,0,2159000
09:40:38 2024/05/14,CHG (COLD),WLC,84,19,4116000,0,2153000
09:41:38 2024/05/14,CHG (COLD),WLC,84,19,4116000,0,2147000
09:42:38 2024/05/14,CHG (COLD),WLC,84,20,4117000,0,2141000
09:43:38 2024/05/14,CHG (COLD),WLC,84,21,4117000,0,2136000
09:44:38 2024/05/14,CHG (COLD),WLC,84,22,4117000,0,2130000
09:45:39 2024/05/14,CHG (COLD),WLC,84,22,4117000,0,2124000
09:46:39 2024/05/14,CHG (COLD),WLC,84,23,4117000,0,2118000
09:47:39 2024/05/14,CHG (COLD),WLC,84,24,4117000,0,2112000
09:48:39 2024/05/14,CHG (COLD),WLC,84,25,4117000,0,2106000
09:49:39 2024/05/14,CHG (COLD),WLC,84,25,4117000,0,2100000
09:50:39 2024/05/14,CHG (COLD),WLC,84,26,4117000,0,2094000
09:51:39 2024/05/14,CHG (COLD),WLC,84,27,4117000,0,2089000
09:52:39 2024/05/14,CHG (COLD),WLC,84,28,4117000,0,2083000
09:53:39 2024/05/14,CHG (COLD),WLC,83,28,4117000,0,2077000
09:54:39 2024/05/14,CHG (COLD),WLC,83,29,4118000,0,2071000
09:55:39 2024/05/14,CHG (COLD),WLC,83,31,4117000,0,2065000
09:56:39 2024/05/14,CHG (COLD),WLC,83,32,4117000,0,2065000
09:57:39 2024/05/14,CHG (COLD),WLC,83,32,4117000,0,2065000
09:58:39 2024/05/14,CHG (COLD),WLC,83,33,4118000,0,2065000
09:59:39 2024/05/14,CHG (COLD),WLC,83,34,4117000,0,2065000
10:00:39 2024/05/14,CHG (COLD),WLC,83,34,4117000,0,2065000
10:01:39 2024/05/14,CHG (COLD),WLC,83,35,4118000,0,2065000
10:02:39 2024/05/14,CHG (COLD),WLC,83,35,4117000,0,2065000
10:03:39 2024/05/14,CHG (GOOD),WLC,83,36,4181000,171000,2065000
10:04:39 2024/05/14,CHG (GOOD),WLC,83,37,4182000,151000,2068000
10:05:39 2024/05/14,EOCHG (GOOD),WLC,83,37,4128000,0,2069000
10:06:39 2024/05/14,EOCHG (GOOD),WLC,84,37,4124000,0,2072000
10:07:39 2024/05/14,EOCHG (GOOD),WLC,84,38,4123000,0,2081000
10:08:39 2024/05/14,EOCHG (GOOD),WLC,85,38,4122000,0,2090000
10:09:39 2024/05/14,DISCHG (GOOD),NONE,85,39,4047000,-189000,2096000
10:10:39 2024/05/14,DISCHG (GOOD),NONE,85,46,4046000,-160000,2092000
10:11:39 2024/05/14,CHG (GOOD),USB,85,57,4179000,224000,2088000

    Hello Jose,
    The last two columns indicate AverageCurrent() and RemainingCapacity(). As you can see from '09:37:38,' my device is in a cold state, which means it won't charge and will use power from the USB port to run. Even if my device still uses the battery for running, why doesn't the AverageCurrent report the accurate current?
    Now, from '10:05:39,' it states that my device is in End Of Charge based on my custom charging profile, and the AverageCurrent is once again 0 mA, which is fine. But why is the RemainingCapacity increasing?

  • +1 in reply to Hoang Nguyen
    Prodigy 10 points

    What is Deadband setting and how can I access to that?