BQ27421: AverageCurrent is always 0

Hank Chu

Expert 1340 points

We used the TI BQ27421 gauge in the project.

1) The value of AverageCurrent( ) Standard Command (0x10 and 0x11) is always 0.

1-1) So, the gauge enters the SLEEP mode because the AverageCurrent() < Sleep Current.

2) The test conditions

2-1) The gauge is on the I2C-bus.

2-2) Because the calibration of the battery is not completed, we downloaded the example of flash stream file into the gauge.

2-2-1) The example of flash stream file does not meet the requirement of the battery in the project.

2-2-1-1) For examples: Design Capacity is 1340 mAh in the flash stream file. But the battery is 9600 mAh.

2-3) The Sleep Current (Subclas 82, offset 31) are set to 10.

Q-3) Is the value of AverageCurrent() always 0 because the flash stream file (without battery calibration) is incorrect for the battery?

Thank you.

over 7 years ago

0 Hank Chu over 7 years ago

Expert 1340 points

We have 1 more question for the gauge.

Q-4) Is the value of AveragePower( ) Standard Command (0x18 and 0x19) always 0 because the flash stream file (without battery calibration) is incorrect for the battery?

Thank you.

0 Dominik Hartl11 over 7 years ago in reply to Hank Chu

TI__Guru 51466 points

The average current is zero when the scaled output from the coulomb counter is below the current dead band setting.

Check the CC Gain parameter (subclass CC Cal 105, offset 4, 4 bytes floating point) and the DeadBand parameter (subclass Current 107, offset 1, 1 byte unsigned integer). They need to match your sense resistor and system deadband.

If the CC Gain parameter is zero then the current will always be zero. If the DeadBand parameter is greater than the actual current then the reported current will also be zero.

0 Hank Chu over 7 years ago in reply to Dominik Hartl11

Expert 1340 points

Thank you very much.

1) About the following 2 parameters, they are not in the example of the flash stream file downloaded into the gauge.

1-1) The CC Gain parameter (subclass CC Cal 105, offset 4)

1-2) The DeadBand parameter (subclass Current 107, offset 1)

2) After we read the content of data memory of the gauge, the default values of the 2 parameters are set as follows:

2-1) CC Gain parameter: 0x7F3209A2

2-2) The Deadband parameter: 0x05

3) About the "system deadband"

3-1) In the Technical Reference, Chapter 6.4.4.3.1 Deadband, it said:

>> Only a few reasons may require changing the default value:
>> 1. If the PCB layout has issues that cause inconsistent board offsets from board to board.
>> 2. An extra noisy environment.

Q3-2) Could you send us the TI document(s) for the calculation of the "system deadband" in our product?

Q-4) About the sense resistor, do you mean the "Integrated Sense Resistor" in the picture below?

Q-4-1) If yes, how to get the value of the "Integrated Sense Resistor" in the bq27421 gauge?

4-1-1) In the datasheet of bq27421, page-1, it said:

>> Low-Value Integrated Sense Resistor
>> (7 mΩ, Typical)

4-1-2) The picture below are captured from the page-1 of the datasheet of bq27421.

###################################################################################

About the example of flash stream file downloaded into the gauge, please refer to the data below.

###################################################################################

;--------------------------------------------------------

;Verify Existing Firmware Version

;--------------------------------------------------------

W: AA 00 01 00

C: AA 00 21 04

W: AA 00 02 00

C: AA 00 08 01

;--------------------------------------------------------

;SET_CFGUPDATE

;--------------------------------------------------------

W: AA 00 13 00

X: 1100

W: AA 3E 02 00

W: AA 40 02 26 00 00 32 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 A5

X: 10

W: AA 3E 02 00

C: AA 60 A5

W: AA 3E 24 00

W: AA 40 00 19 28 63 5F FF 62 00 32 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 69

X: 10

W: AA 3E 24 00

C: AA 60 69

W: AA 3E 30 00

W: AA 40 0E 10 FD FF 38 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 AD

X: 10

W: AA 3E 30 00

C: AA 60 AD

W: AA 3E 31 00

W: AA 40 0A 0F 02 05 32 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 AD

X: 10

W: AA 3E 31 00

C: AA 60 AD

W: AA 3E 40 00

W: AA 40 25 F8 0F 00 00 14 04 00 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 B2

X: 10

W: AA 3E 40 00

C: AA 60 B2

W: AA 3E 44 00

W: AA 40 05 00 32 01 C2 14 14 00 03 08 98 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 39

X: 10

W: AA 3E 44 00

C: AA 60 39

W: AA 3E 50 00

W: AA 40 02 BC 01 2C 00 1E 00 C8 C8 14 08 00 3C 0E 10 00 0A 46 05 14 05 0F 03 20 00 64 46 50 0A 01 90 00

W: AA 60 BB

X: 10

W: AA 3E 50 00

C: AA 60 BB

W: AA 3E 50 01

W: AA 40 64 19 DC 5C 60 00 7D 00 04 03 19 25 0F 14 0A 78 60 28 01 F4 00 00 00 00 00 00 43 80 04 01 14 00

W: AA 60 2A

X: 10

W: AA 3E 50 01

C: AA 60 2A

W: AA 3E 50 02

W: AA 40 0B 0B B8 01 2C 0A 01 0A 00 00 00 C8 00 64 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 C1

X: 10

W: AA 3E 50 02

C: AA 60 C1

W: AA 3E 51 00

W: AA 40 00 A7 00 64 00 FA 00 3C 3C 01 B3 B3 01 90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 8A

X: 10

W: AA 3E 51 00

C: AA 60 8A

W: AA 3E 52 00

W: AA 40 40 00 00 00 00 81 0E DB 0E A8 05 3C 13 60 05 3C 0C 80 00 C8 00 32 00 14 03 E8 01 00 64 10 04 00

W: AA 60 AC

X: 10

W: AA 3E 52 00

C: AA 60 AC

W: AA 3E 52 01

W: AA 40 0A 10 5E FF CE FF CE 00 01 02 BC 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 2E

X: 10

W: AA 3E 52 01

C: AA 60 2E

W: AA 3E 53 00

W: AA 40 01 28 10 63 E5 E5 E8 E7 EA EA EC EC EE EE F0 F1 F1 EF EB EC ED F0 F6 F7 F9 F9 FB FC FC FF FF FE

W: AA 60 FF

X: 10

W: AA 3E 53 00

C: AA 60 FF

W: AA 3E 53 01

W: AA 40 FB F6 F4 EE EB F6 FA E1 F6 DF 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 1B

X: 10

W: AA 3E 53 01

C: AA 60 1B

W: AA 3E 54 00

W: AA 40 FF 2B 05 01 01 00 00 FF FF 00 00 FE FE FE FF 01 03 09 05 FD FE FF FF FF FF FE FD FC F5 EE F2 F4

W: AA 60 0E

X: 10

W: AA 3E 54 00

C: AA 60 0E

W: AA 3E 54 01

W: AA 40 FE 04 02 02 06 08 FE FB 9C 81 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 D5

X: 10

W: AA 3E 54 01

C: AA 60 D5

W: AA 3E 55 00

W: AA 40 FF BA 00 00 F9 E5 28 17 D1 1F 07 08 01 09 13 E0 EA 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 43

X: 10

W: AA 3E 55 00

C: AA 60 43

W: AA 3E 6C 00

W: AA 40 FF 00 00 00 F2 08 CE DB E6 C2 D3 E5 12 FF 2E 65 1A 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 3F

X: 10

W: AA 3E 6C 00

C: AA 60 3F

W: AA 3E 59 00

W: AA 40 00 66 00 66 00 63 00 6B 00 48 00 3B 00 3E 00 3F 00 35 00 2F 00 3C 00 46 00 8C 01 71 02 4C 00 00

W: AA 60 33

X: 10

W: AA 3E 59 00

C: AA 60 33

W: AA 3E 70 00

W: AA 40 80 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

W: AA 60 FF

X: 10

W: AA 3E 70 00

C: AA 60 FF

;--------------------------------------------------------

;Exit CFGUPDATE

;--------------------------------------------------------

W: AA 00 00 00

W: AA 00 42 00

X: 2000

0 Dominik Hartl11 over 7 years ago in reply to Hank Chu

TI__Guru 51466 points

I'm sorry, I overlooked that the bq27421 has the sense resistor integrated.
The CC gain parameter is set during production at TI so it's not necessary to change this parameter by the customer.

The Deadband parameter is very simple. It is a threshold for the reported current. If the measured current is less than the Deadband setting then the gauge will set the reported current to zero.

0 Hank Chu over 7 years ago in reply to Dominik Hartl11

Expert 1340 points

Thank you very much.

Currently, the AverageCurrent() of the gauge on our product is always 0.
According to your information, we will focus on the Deadband parameter for this problem.

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BQ27421: AverageCurrent is always 0