TI Single-Cell Fuel Gauge Basic Introduction and FAQs

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TI Single-Cell Fuel Gauge Basic Introduction and FAQs [Copy link]

The gas gauge/fuel gauge is used to measure and display the battery power, usually including the remaining capacity (RM), full charge capacity (FCC), percentage capacity (SOC), voltage, current, temperature, etc. Some gas gauges also include empty and full time. TI impedance tracking gas gauges have two other important parameters, Qmax (maximum chemical capacity, which refers to the capacity from full charge to full discharge with a very small current) and impedance table (the important one is Ra table at 25 degrees (some very old models are 0 degrees)). Laptop gas gauges (2-4 strings) also have very complete protection functions.

Frequently Asked Questions:

Q: What are the benefits of using a fuel gauge and what applications require it?

Generally speaking, rechargeable batteries are the application scenarios of fuel gauges, which depends on many considerations such as cost and user experience.

Benefits: 1. Improve user experience (can accurately know the power level without large unreasonable jumps. The traditional simple voltage method is prone to abnormal jumps, and the simple coulomb meter will have cumulative errors and need to be updated and calibrated frequently)

2. Discharge the battery as much as possible to extend the usage time (obtaining accurate power information can ensure that a lower shutdown voltage is used without sudden crashes)

3. Cost-effectiveness. Under the premise of 2, the extra power that can be discharged from a large-capacity battery may be more expensive than the cost of a power meter. In addition, avoiding the use of high-energy-density batteries in situations where the volume is limited can also bring cost optimization.

Q: Why is it so difficult to improve the accuracy of the fuel gauge?

The battery model is very complex, there are many types of battery cells, there are many nonlinear parameters, the discharge curve is greatly affected by temperature, load, etc., and the internal resistance of the battery will change significantly with aging, discharge depth and temperature.
The load conditions of different systems are relatively complex. Some systems have very fast current changes, current spikes, and a wide current change range.
Q: The reason for the high accuracy of TI fuel gauges

Mature professional algorithm impedance tracking can track the changes in battery parameters very well, maintain good accuracy in low temperature and aging conditions, and also have good accuracy in the first cycle of power-on. You only need to download the mass production file, and there is no need to cycle and age each battery. The basic content of the algorithm is http://www.ti.com/litv/pdf/slua450.
We have a lot of experience in battery research and customer feedback, and have accumulated rich battery knowledge. We continuously improve the characteristics of the fuel gauge through customer feedback information.
Hardware advantages, using dual high-precision 15-16-bit ADC and low-power microcontroller

Q: What kind of battery material does TI power support?

Currently, TI impedance tracking algorithm power mainly supports lithium batteries, including cobalt, manganese lithium, iron lithium and ternary materials. Among them, BQ27425 BQ27421/441 with fixed battery cell information currently does not support iron lithium and needs to select different suffix models according to the material. Other models of fuel gauges need to download corresponding battery cell information for specific materials.

Q: TI single-cell fuel gauge product classification and how to select

The models currently promoted by TI are BQ27541 BQ27741 BQ27510 BQ27520 BQ27531/530 BQ27421/441 BQ27425

Consider packaging BQ27741 BQ27520 BQ27425BQ27530/BQ27531 are all CSP packages, which have relatively high process requirements for many applications. BQ27541 BQ27510 BQ27441/BQ27421 (421 is a 9-ball CSP, which does not require via layout) packaging is conducive to improving mass production yield and test
accuracy and cost requirements. BQ27541 BQ27741 BQ27510 BQ27520 BQ27531/530 has a design accuracy of 1%, is based on Flash, and has a relatively high cost. BQ27421/441 The design accuracy of BQ27425 is 5%. BQ27425 is medium cost. The storage device of BQ27421/441 is ROM, which is low cost.
System-side and battery-side, BQ27541/BQ27741 is a battery-side (packside) fuel gauge, which is usually placed in the battery pack. The entire production is completed by the battery manufacturer, and the accuracy is also higher. The system user only needs to complete the I2C read and write capacity information command. The development difficulty is very low, and it can be used for battery identification. The disadvantage is that the cost of the entire solution will be slightly higher. The remaining fuel gauges are system-side fuel gauges, which are placed on the motherboard. The system user needs to complete the debugging process such as parameter configuration, which will be slightly complicated.
Other factors, BQ27741 is a power gauge with protection function, which can set more flexible protection.
BQ27530/531 has a charger control function, which can achieve charging optimization

BQ27425/BQ27421 is a fuel gauge with integrated current sampling resistor, and the maximum long-term discharge current only supports 2A

BQ27421/BQ27441 is a simple and easy-to-use electricity meter with a simple configuration parameter process, suitable for single-chip control occasions

BQ27620 is a voltage-only electricity meter and is relatively complex to use. It is recommended to contact FAE before selecting the model.

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Q: What tools are needed to develop a fuel gauge?

Evaluation board EVM and downloader EV2400/EV2300
host computer software, currently mainly EVSW, BqCONFIG and Gauge studio, usually can be downloaded from the software link below the specific part number on the official website. BqCONFIG is mainly used to configure the power meter parameters step by step to generate mass production files, EVSW is used to record debugging data, update configuration files, etc. Gauge studio is an upgraded version of EVSW, and new models will gradually use this software to replace EVSW and BqCONFIG
Gaugestudio http://www.ti.com/litv/zip/sluc424c

BQ275XX EVSW http://www.ti.com/litv/zip/sluc367c

bqCONFIG http://www.ti.com/litv/zip/sluc378d

Battery cells or battery packs, electronic loads, power supplies, precision multimeters, and if low-temperature testing is required, a temperature chamber is also required.
Q: Can the entire development process be completed using only a single-chip microcomputer without using EV2400/2300?

Without using the evaluation kit from the official website, it is impossible to use the host computer to perform relevant configuration, debugging, and generate mass production files. Especially for the power meters such as BQ275XX and BQ27741 that need to burn the cell characteristic parameters (CHEM-ID), these parameters cannot be burned only by the microcontroller during the development stage. Even for the power meters such as bq27421/441 that can be configured by the microcontroller, the lack of good debugging tools will also lead to low development efficiency.

Q: EV2300 cannot be used after connecting to the computer

EV2300 does not work on some computers. To solve this problem, try installing the driver software (there are 32-bit and 64-bit versions of the driver). If that doesn't work, it is recommended to replace it with EV2400.

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Q: How to complete the development process and obtain mass production documents?

The development steps mainly include: 1. Configuration parameters 2. Calibration 3. Cell curve CHEM-ID selection 4. Golden learning 5. Export mass production files

1. Configuration parameters can be configured through bqCONFIG or bqEASY in EVSW. The most common way is to modify the parameters in dataMemory through EVSW or Gauge studio. The main parameters (some power meters may not display all parameters, so you can leave them blank) are

Parameters for judging full charge condition

->Charge Voltage Full charge voltage, charger constant voltage charging voltage

->Taper Current is the current when fully charged. It is generally set to be about 25mA higher than the current when the charger stops charging (note that the filling method for BQ27425, BQ27421/441 is slightly different. The conversion value is Taper current (value) = Design Capacity*10/Taper current (mA))

->Taper Voltage is used to determine whether the battery meets the full charge conditions. It is generally set to 100 or 150mV, which is 100-150mV lower than the charging voltage.

Battery capacity information

->Design Capacity is filled in according to the nominal capacity of the battery cell

->Design Energy is filled in according to the battery cell's nominal energy (4.2V cobalt lithium is nominal capacity*3.7, 4.35V fully charged voltage battery is nominal capacity*3.8)

System information (Note that the filling method for BQ27425, BQ27421/441 is slightly different, the conversion value is Threshold (value) = Design Capacity*10/Threshold (mA))

->Terminate Voltage The minimum operating voltage for normal system operation

->Dsg Current Threshold discharge threshold

->Chg Current Threshold charging threshold

->Quit Current

Other information, including interrupt pin function, temperature sensor selection, etc., can be filled in as needed

2. Calibration

First, make sure that the CC offset is calibrated without load and charging current, then calibrate the board offset, and then add a 1A discharge current and fill in the actual current value through the multimeter to calibrate the Pack current

There is no order for voltage and temperature calibration. You need to ensure that the battery or power supply voltage value is stable and then read the actual value through a multimeter for calibration.

For fuel gauges with integrated sampling resistors, there is no need to calibrate the pack current.

3.CHEM-ID selection

Battery A is first charged with a constant current of 0.5C and a constant voltage taper current of less than 0.01C.

B. Leave to stand for 2 hours

C connects to the EVM board and automatically logs the DataRAM data every 4 seconds

D starts discharging with a current of 0.1C until it reaches 2.8V

EStand for 5 hours

F Save the above log data and use MATHCAD program to calculate CHEM_ID. The software link is http://www.ti.com/litv/zip/sluc138bh

G Download CHEM_ID through the corresponding interface of bqCONFIG/EVSW/Gauge studio

Note that the board must be calibrated before doing CHEM_ID. The discharge process must be continuous. The recorded data includes the 5 hours of static time after discharge. BQ27425/BA27421/441 does not require this step. You only need to select the corresponding model.

4.Learn and export production files in a loop

A. Confirm that the relevant parameters have been set, calibration and CHEM_ID selection have been performed before this step can be performed. Send command 0x41 to reset and export DFI file or SENC file for backup

B. Prepare an empty battery cell (voltage between 3.0V-3.3V) and let it sit for 5 hours.

C. Connect the board and send the 0x0021 command to enable the IT algorithm. It is recommended to automatically record the Data RAM data (4s interval) and the Data FLash data (10 minutes interval)

D. Charge the battery fully according to the normal charging process, then let it stand for 2 hours, then discharge it to the cut-off voltage at 0.2C current, and let it stand for another 5 hours to ensure that the update status value is 0x06

E. Export the gg file of DataFlash, open it with Notepad and modify Update Status to 0x02 and Cycle Count to 0

F. Import the previously backed up DFI or senc file, and then write the modified gg file

G. Generate DFI, dffs files

Note: The test process is carried out at room temperature. The iron-lithium battery requires a longer standing time. A, E, and F are only for the pack side fuel gauge BQ27541 and BQ27741. For bq27421/441, step G is not required. You only need to get the gg file. The DFI file corresponding to BQ27425 is called DMI file. BQ27421/441 and BQ27425 do not need to send the 0x0021 command. For BQ275XX and BQ27741, it is necessary to confirm the sending of enable (0x0021) and seal command (0x0020) in actual mass production. BQ27421/441BQ27425 needs to send the seal command (0x0020)

martin0221

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华华@太阳花

Thanks for sharing, I learned a lot