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PS200-I/SO

PowerSmart® Configurable Battery Charger

Microchip Technology 

2.0 LITHIUM CHEMISTRY

ALGORITHM

The PS200 provides an unprecedented level of

configurability for charging Lithium Ion/Lithium Polymer

battery packs. It’s precision, 10-bit Analog-to-Digital

converter and high-frequency Pulse-Width Modulator

enable the PS200 to provide optimum control of

charging algorithms for lithium battery chemistries.

Special features include an internal voltage regulator

and an internal clock oscillator that reduce external

component count.

2.1 Lithium Overview

2.1.1 MULTI-STEP CHARGING

To ensure the proper treatment of lithium chemistries

during extreme temperature and voltage conditions,

multi-step charging is required. The PS200 starts the

charging cycle upon sensing the presence of a battery

pack and a valid charging supply. During charge

qualification, the battery’s temperature and voltage are

measured to determine the appropriate initial state.

The initial states include Charge Suspend, Precharge

and Current Regulation. Charge Suspend halts

charging when the user defined preset conditions for

charging are not met. Precharge allows for the

recovery of deeply discharged batteries by applying a

low-charge current. Current Regulation provides

constant current, voltage limited charge. Upon

reaching the target voltage during Current Regulation,

the Voltage Regulation state is entered. Charging

continues at a constant voltage until the current

decreases to the user specified minimum current

threshold (VRIMin). At this threshold, charging is

terminated and the End-Of-Charge state is reached.

The state diagram illustrates the charging cycle (see

Figure 2-1).

PS200

2.1.2

USER CONFIGURABLE

PARAMETERS

The PS200 supports user configurable parameters that

allow for customizing the charging profile. This feature

allows for the maximum reuse of hardware, thus

reducing time-to-market. These parameters include:

• Battery Temperature:

- Minimum/maximum temperature for charge

initiation

- Maximum temperature allowed during charge

• Battery Voltage:

- Minimum/maximum voltage for charge

initiation

- Target voltage during Voltage Regulation

- Voltage at which the charger will restart

charging after completion of a valid charge

cycle

• Charge Current:

- Target current during Current Regulation

- Taper current threshold for End-Of-Charge

during Voltage Regulation

- Target current during Precharge

• Time:

- Precharge time limit

- Current Regulation time limit

- Voltage Regulation time limit

• Status Display:

- Two LEDs denote the charge states. Their

flash rates can be modified.

© 2005 Microchip Technology Inc.

DS21891B-page 5

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