MCP73841 datasheet(11/24 Pages) MICROCHIP

11 / 24 page

 2004 Microchip Technology Inc.

DS21823B-page 11

MCP73841/2/3/4

4.0

DEVICE OVERVIEW

The MCP7384X family of devices are highly advanced,

linear charge management controllers. Figure 4-1

depicts the operational flow algorithm from charge

initiation to completion and automatic recharge.

4.1

Charge Qualification and

Preconditioning

Upon insertion of a battery or application of an external

supply, the MCP7384X family of devices automatically

perform a series of safety checks to qualify the charge.

The input source voltage must be above the

undervoltage lockout threshold, the enable pin must be

above the logic-high level and the cell temperature

monitor must be within the upper and lower thresholds.

The cell temperature monitor applies to both the

MCP73841 and MCP73842, with the qualification

parameters being continuously monitored. Deviation

beyond the limits automatically suspends or terminates

the charge cycle.

Once the qualification parameters have been met, the

MCP7384X initiates a charge cycle. The charge status

output is pulled low throughout the charge cycle (see

Table 5-1 for charge status outputs). If the battery

voltage is below the preconditioning threshold (VPTH),

the MCP7384X preconditions the battery with a trickle-

charge. The preconditioning current is set to

approximately 10% of the fast charge regulation

current. The preconditioning trickle-charge safely

replenishes deeply depleted cells and minimizes heat

dissipation in the external pass transistor during the

initial charge cycle. If the battery voltage has not

exceeded the preconditioning threshold before the

preconditioning timer has expired, a fault is indicated

and the charge cycle is terminated.

4.2

Constant-Current Regulation –

Fast Charge

Preconditioning ends and fast charging begins, when

the battery voltage exceeds the preconditioning

threshold. Fast charge regulates to a constant-current,

IREG, based on the supply voltage minus the voltage at

the SENSE input (VFCS) developed by the drop across

an external sense resistor (RSENSE). Fast charge

continues until the battery voltage reaches the

regulation voltage (VREG); or until the fast charge timer

expires. In this case, a fault is indicated and the charge

cycle is terminated.

4.3

Constant-Voltage Regulation

When the battery voltage reaches the regulation

voltage (VREG), constant-voltage regulation begins.

The MCP7384X monitors the battery voltage at the

VBAT pin. This input is tied directly to the positive

terminal of the battery. The MCP7384X is offered in

four fixed-voltage versions for single or dual series cell

battery packs with either coke or graphite anodes:

- 4.1V (MCP73841-4.1, MCP73843-4.1)

- 4.2V (MCP73841-4.2, MCP73843-4.2)

- 8.2V (MCP73842-8.2, MCP73844-8.2)

- 8.4V (MCP73842-8.4, MCP73844-8.4)

4.4

Charge Cycle Completion and

Automatic Re-Charge

The MCP7384X monitors the charging current during

the constant-voltage regulation phase. The charge

cycle is considered complete when the charge current

has diminished below approximately 7% of the

regulation current (IREG) or the elapsed timer has

expired.

The MCP7384X automatically begins a new charge

cycle when the battery voltage falls below the recharge

threshold (VRTH), assuming all the qualification

parameters are met.

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