MCP73864-I/SL 데이터 시트보기 (PDF) - Microchip Technology

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MCP73864-I/SL

Advanced Single or Dual Cell, Fully Integrated Li-Ion/Li-Polymer Charge Management Controllers

Microchip Technology 

MCP73861/2/3/4

Preconditioning

Mode

Regulation

Voltage

(VREG)

Regulation

Current

(IREG)

Constant-Current

Mode

Constant-Voltage

Mode

Transition

Threshold

(VPTH)

Charge

Voltage

Precondition

Current

(IPREG)

Termination

Current

(ITERM)

Precondition

Safety Timer

Charge

Current

Fast Charge

Safety Timer

Elapsed Time

Termination Timer

FIGURE 6-3:

Typical Charge Profile in Thermal Regulation.

6.1 Application Circuit Design

Due to the low efficiency of linear charging, the most

important factors are thermal design and cost, which

are a direct function of the input voltage, output current

and thermal impedance between the battery charger

and the ambient cooling air. The worst-case situation is

when the device has transitioned from the

Preconditioning mode to the Constant-current mode. In

this situation, the battery charger has to dissipate the

maximum power. A trade-off must be made between

the charge current, cost and thermal requirements of

the charger.

6.1.1 COMPONENT SELECTION

Selection of the external components in Figure 6-1 is

crucial to the integrity and reliability of the charging

system. The following discussion is intended as a guide

for the component selection process.

6.1.1.1 Current Programming Resistor

(RPROG)

The preferred fast charge current for Lithium-Ion cells

is at the 1C rate, with an absolute maximum current at

the 2C rate. For example, a 500 mAh battery pack has

a preferred fast charge current of 500 mA. Charging at

this rate provides the shortest charge cycle times

without degradation to the battery pack performance or

life.

1200 mA is the maximum charge current obtainable

from the MCP7386X. For this situation, the PROG input

should be connected directly to VSS.

6.1.1.2 Thermal Considerations

The worst-case power dissipation in the battery

charger occurs when the input voltage is at the

maximum and the device has transitioned from the Pre-

conditioning mode to the Constant-current mode. In

this case, the power dissipation is:

PowerDissipation = VDDMAX – VPTHMIN  IREGMAX

Where:

VDDMAX = the maximum input voltage

IREGMAX = the maximum fast charge current

VPTHMIN = the minimum transition threshold

voltage

DS21893F-page 20

 2004-2013 Microchip Technology Inc.

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