Android4.4 battery management

Android4.4 battery management

I. Overview

The battery management function of Android4.4 is used to manage the battery charging and discharging functions. The entire battery management includes four parts: Linux battery drive, Android battery service, battery attributes and parameters, and battery curve optimization.

The Linux battery driver is used to interact with PMIC and listen for events related to the battery, such as low-power alarms, power changes, high-temperature alarms, and USB plugging.

The Android battery service monitors the battery events reported by the kernel and reports the latest battery data to the system. After receiving the new data, the system updates the battery display status, remaining power, and other information. If you receive temperature and low-power alarms, the system will automatically trigger the shutdown process to protect the battery and machine from harm.

The Study of battery attributes and parameters is also very important to improve the performance of the battery subsystem. The better the battery performance, the more accurate the reported data. Therefore, developers also need to have a deep understanding of this. Battery curve optimization is very important. The better the battery curve, the more accurate the displayed power ratio, the better the linearity of the discharge curve. Therefore, the optimization of the discharge curve is the most important.

Ii. Android battery service

1. Start and run the Android battery service

2. source code structure of the Android battery service <喎?http: www.bkjia.com kf ware vc " target="_blank" class="keylink"> VcD4KPHA + Environment + 8 + Environment + rHku6 + 1 xLnjsqXP + 8 + Environment + io6yyos2o1qrG5Mv7xKO/6TwvcD4KPHA + Environment + region + tszus + S9 + Milo6w8YnI + region + 1zbO3/s7x1tA8YnI + region + CjxwPiA8L3A + region + cjxwifsawdupq = "center">

Iii. Battery attributes and Parameters

1. Six Main Parameters of Lithium Battery

A. Battery Capacity

The battery capacity is determined by the number of active substances in the battery, which is usually expressed by mAh or Ah. For example, 1000mAh is able to discharge 1 h with 1A current.

The total charge is about 3600C.

B. Nominal voltage

The potential difference between the positive and negative batteries is called the nominal voltage. The nominal voltage is determined by the electrode potential of the plate material and the concentration of the internal electrolyte. Lithium Battery release

The electrical diagram is parabolic, with 4.3V dropping to 3.7V and 3.7V dropping to 3.0V quickly changing. Only about 3.7V has the longest discharge time, accounting for almost

Therefore, the nominal voltage of the lithium battery is the voltage that maintains the longest discharge time. The nominal voltages of lithium battery are 3.7V and 3.8 V, such

If it is 3.7 V, the charging termination voltage is 4.2 V. If it is 3.8 V, the charging termination voltage is 4.35 V.

C. Charge termination Voltage

When the rechargeable battery is fully powered, the active substance on the plate has reached the saturation state, and then continue charging, the battery voltage will not rise, the voltage at this time

It is called the charging termination voltage. The charging termination voltage of the lithium-ion battery is 4.2V or 4.35 V.

D. Discharge termination Voltage

Discharge voltage refers to the minimum voltage allowed when the battery is discharged. The discharge termination voltage is related to the discharge rate. The discharge termination voltage of the lithium-ion battery is 2.7 V.

E. Internal Resistance of the battery

The internal resistance of the battery depends on the resistance of the plate and the impedance of the ion stream. In the process of charge and discharge, the resistance of the plate remains unchanged, but the impedance of the ion stream

Changes with the increase or decrease of electrolyte concentration and charged ions. When the OCV voltage of the lithium battery is reduced, the impedance increases. Therefore, when the power is low

First pre-charge, to prevent high current caused by excessive heat of the battery.

F. Self-Discharge Rate

It refers to the percentage of automatically lost power in a period of time when the battery is not used. Lithium Battery self-discharge rate at normal temperature

In 5% ~ 8%.

2. Working Principle of Lithium Battery

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3. Lithium Battery Charging Method

Lithium battery charging is completed in three steps: Pre-charging, cross-flow charging, and constant voltage charging.

Step 1: when the voltage is less than 3 V, you must first perform pre-Charging. The pre-charging current is generally 10% of the charging current, and the pre-charging end condition is Vbat.

The pressure reaches 3 V;
Step 2: when the voltage is greater than 3 V and less than V, constant current charging is usually 0.2C ~ 1C;

Step 3: When the Vbat voltage reaches 4.2V, the constant voltage is charged, and the charging current is gradually reduced.

The charge ends at 15% or 20% of the current. If the Kulun meter is used, the condition of charge end must be added to whether the battery of the Kulun meter has been reached.

100%;

4. Discharge mode of Lithium Battery

Note the following:

A. the discharge current cannot be too large. Excessive Current leads to internal heat of the battery, which may cause permanent damage;

B. Never discharge too much. Lithium batteries are most afraid of discharge. Once the OCV voltage is lower than 2.7 V, the battery may be decommissioned;

C. The higher the discharge current of the battery, the smaller the discharge capacity and the faster the voltage drop. Therefore, when the battery is working at a high load, the voltage will rise when the load is reduced.

This is the so-called "back-to-power" phenomenon;

Iv. Battery Curve

The battery curve includes the Charging Curve and discharge curve. The user generally pays more attention to the linearity of the discharge curve.

1. Calculation of remaining power by PMU

PMU can calculate the remaining battery power in two ways: one is calculated by the OCV voltage, and the other is calculated by the electric meter. When using

When calculating the remaining power, the electric meter must work with the OCV to correct the remaining capacity. The remaining power calculated by the PMU register when the discharge starts from 100%

The amount is calculated based on the electric meter. when the power is reduced to 95%, PMU will refer to OCV and then correct the remaining power calculated by the power. When

When the remaining power is reduced to less than 95%, the remaining power is subject to the electric meter. When the power consumption is reduced to 7%, PMU will refer to OCV again to correct the power consumption.

The remaining power. When the power is reduced to less than 7%, the remaining power is charged by the electric meter.

2. Factors affecting the accuracy of battery Curves

The main influencing factors include the internal resistance (RDC) of the battery, the battery capacity, the activation status of the new battery, and the method for measuring the battery curve.

A. Internal Resistance of the battery

Theoretically, the smaller the internal resistance of the battery, the more accurate the tested curve. When the battery is in use, the internal resistance of the battery also changes, so the internal resistance of the battery is

The variation will affect the accuracy of the battery curve;

B. Battery Capacity

When the battery leaves the factory, the manufacturer will give the nominal capacity of the battery. In some cases, the nominal capacity of the battery is different from the actual capacity,

In this way, the linearity of the battery discharge curve is also affected. Therefore, it is best to use a measurement tool to measure the actual battery capacity.

C. activation status of new battery

The battery is not fully activated when the battery is released. In this case, the relationship between the OCV and the actual battery is unstable and inaccurate because

The new battery requires multiple full charge/discharge times before testing the battery curve.

D. Method for Measuring the battery Curve

If the method for measuring the battery curve is incorrect, the linearity of the measured battery curve will also be poor. For example, the connection line between the test board and the battery

Too long and too fine, this will make the RDC of the battery too large, the tested curve is not accurate. Therefore, when measuring, try to avoid increasing

RDC with battery.

In addition, the number of measurements should be as many as possible, because sometimes some environmental factors also affect the measurement results.