Datasheet > AN-9721

AN-9721

更新时间： 2022-10-09 17:48:23

品牌	Logo	应用领域
飞兆/仙童 - FAIRCHILD		电池
页数	文件大小	规格书
4页	124K
描述
Li-Ion Battery Charging Basics

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AN-9721 数据手册

www.fairchildsemi.com

AN-9721

Li-Ion Battery Charging Basics, Featuring the

FAN5400 / FAN5420 Family of PWM Battery Chargers

Overview

Today’s cell phones and other handheld devices provide

ever increasing functionality and a richer user experience.

As their functionality increases, the demand for battery

power increases as well, which leads to adoption of higher-

capacity batteries. These higher-capacity batteries require

high-current charging solutions, which can best be served

with efficient PWM chargers.

PROTECTION

CIRCUIT

CELL

ESR

–

CONTROL

Lithium-Ion battery charging is simplified with modern IC

charging solutions. This application note provides a guide

for how to use the FAN5400 and FAN5420 family of PWM

chargers for high-current, fast-charging solutions to

minimize the charging time while providing full compliance

to modern battery safety specifications.

Figure 1.

Li-Ion Battery Pack

During charging, assuming the battery was not too deeply

discharged, a constant current I_CHARGEis provided until the

battery’s voltage has risen to V_FLOAT. The maximum float

voltage is typically specified by the battery manufacturer

and is programmed into the charger IC through the OREG

Lithium-Ion Battery Charging Basics

A Li-Ion battery charger must provide a constant current to

the battery until the battery voltage has reached its “float”

voltage. The battery can be thought of as a very large

capacitor in series with a small resistance that represents its

ESR (equivalent series resistance). Inside every battery pack

is a protection IC, which features two back-to-back

MOSFETs and an analog control circuit that prevents over-

charging and over-discharging by monitoring the cell

voltage and discharge current. The protection circuit is

referred to as “secondary protection” because the charging

system must also ensure that the battery is not overcharged.

The protection circuit provides a back-up safety circuit

where overcharging is concerned.

When V_BAT, the voltage at the battery terminals, reaches

_FLOAT, I_CHARGEis limited by the cell voltage, V_CELL:

V_BAT−V_CELL

(1)

I_CHARGE

R_ESR

As the internal cell voltage rises to approach V_BAT, the

charge current continues to decrease until it reaches a

termination current, which is commonly set for 10% of the

full charge current.

OREG

FLOAT

I_CHARGE

Note:

1C Current

OCHARGE

1. For functional clarity, Q1 and Q2 are shown as PMOS

MOSFETs in series with the positive leg in Figure 1.

Most protection circuits use NMOS MOSFETs in the

return leg instead for lower cost.

I_TERM

SHORT

The protection circuit’s resistance should be considered to

be part of the battery’s total ESR.

SHORT

PRECHARGE

PRE-

CHARGE

CURRENT REGULATION

VOLTAGE

REGULATION

Figure 2.

Li-Ion Charge Profile

Rev. 1.0.0 • 12/23/10

www.fairchildsemi.com

12 3 4

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