MCP73828 datasheet(9/24 Pages) MICROCHIP

9 / 24 page

 2002 Microchip Technology Inc.

DS21706A-page 9

MCP73828

4.0

DEVICE OVERVIEW

The MCP73828 is a linear charge management con-

troller. Refer to the functional block diagram on page 2

and the typical application circuit, Figure 6-1.

4.1

Charge Qualification and

Preconditioning

Upon insertion of a battery or application of an external

supply, the MCP73828 automatically performs a series

of safety checks to qualify the charge. The SHDN pin

must be above the logic high level, and the cell temper-

ature monitor must be within the upper and lower

threshold limits. The qualification parameters are con-

tinuously monitored. Deviation beyond the limits, auto-

matically suspends the charge cycle.

After the qualification parameters have been met, the

MCP73828 initiates a charge cycle. The charge com-

plete output, CD10, is pulled low throughout the pre-

conditioning and controlled current phases (see

Table 5-1 for charge complete outputs). If the cell volt-

age is below the preconditioning threshold, 2.4V typi-

cally, the MCP73828 preconditions the cell with a

scaled back current. The preconditioning current is set

to approximately 43% of the fast charge peak current.

The

preconditioning

safely

replenishes

deeply

depleted cells and minimizes heat dissipation in the

external pass transistor during the initial charge cycle.

4.2

Controlled Current Regulation - Fast

Charge

Preconditioning ends and fast charging begins when

the cell voltage exceeds the preconditioning threshold.

Fast charge utilizes a foldback current scheme based

on the voltage at the VSNS input developed by the drop

across an external sense resistor, RSENSE, and the out-

put voltage, VBAT. Fast charge continues until the cell

voltage reaches the regulation voltage, VREG.

4.3

Constant Voltage Regulation

When the cell voltage reaches the regulation voltage,

VREG, constant voltage regulation begins. The

MCP73828 monitors the cell voltage at the VOUT pin.

This input is tied directly to the positive terminal of the

battery. The MCP73828 is offered in two fixed-voltage

versions for battery packs with either coke or graphite

anodes:

4.1V

(MCP73828-4.1)

and

4.2V

(MCP73828-4.2).

4.4

Charge Cycle Completion

The charge cycle can be terminated by a host micro-

controller when the charge current has diminished

below approximately 10% of the peak output voltage

level. The charge complete output will go to a high

impedance state signaling when the charge can be ter-

minated. The charge is terminated by pulling the shut-

down pin, SHDN, to a logic Low level.

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