MCP73861T-ISLASHML datasheet(13/28 Pages) MICROCHIP

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DS21893C-page 13

MCP73861/2/3/4

4.0

DEVICE OVERVIEW

The MCP7386X family of devices are highly advanced

linear charge management controllers. Refer to the

functional block diagram. Figure 4-2 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 MCP7386X family of devices automatically

performs a series of safety checks to qualify the

charge. The input source voltage must be above the

Undervoltage Lockout (UVLO) threshold, the enable

pin must be above the logic-high level and the cell

temperature must be within the upper and lower

thresholds.

The

qualification

parameters

are

continuously monitored. Deviation beyond the limits

automatically suspends or terminates the charge cycle.

The input voltage must deviate below the UVLO stop

threshold for at least one clock period to be considered

valid.

Once the qualification parameters have been met, the

MCP7386X 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 MCP7386X preconditions the battery with a trickle-

charge. The preconditioning current is set to approxi-

mately 10% of the fast charge regulation current. The

preconditioning

trickle-charge

safely

replenishes

deeply depleted cells and minimizes heat dissipation

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 thresh-

old. Fast charge regulates to a constant current (IREG),

which is set via an external resistor connected to the

PROG pin. Fast charge continues until the battery

voltage reaches the regulation voltage (VREG), or the

fast charge timer expires; in which 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 MCP7386X monitors the battery voltage at the

VBAT pin. This input is tied directly to the positive

terminal of the battery. The MCP7386X selects the

voltage regulation value based on the state of VSET.

With VSET tied to VSS, the MCP73861/3 and

MCP73862/4 regulate to 4.1V and 8.2V, respectively.

With VSET tied to VDD, the MCP73861/3 and

MCP73862/4 regulate to 4.2V and 8.4V, respectively.

4.4

Charge Cycle Completion and

Automatic Re-Charge

The MCP7386X monitors the charging current during

the Constant-voltage regulation mode. The charge

cycle is considered complete when the charge current

has diminished below approximately 8% of the

regulation current (IREG), or the elapsed timer has

expired.

The MCP7386X automatically begins a new charge

cycle when the battery voltage falls below the recharge

threshold

(VRTH), assuming all the qualification

parameters are met.

4.5

Thermal Regulation

The MCP7386X family limits the charge current based

on the die temperature. Thermal regulation optimizes

the charge cycle time while maintaining device reliabil-

ity. If thermal regulation is entered, the timer is automat-

ically slowed down to ensure that a charge cycle will

not terminate prematurely. Figure 4-1 depicts the

thermal regulation profile.

FIGURE 4-1:

Typical Maximum Charge

Current vs. Die Temperature.

4.6

Thermal Shutdown

The MCP7386X family suspends charge if the die

temperature exceeds 155°C. Charging will resume

when the die temperature has cooled by approximately

10°C. The thermal shutdown is a secondary safety

feature in the event that there is a failure within the

thermal regulation circuitry.

200

400

600

800

1000

1200

1400

100

120

140

Die Temperature (° C)

Minimum

Maximum

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