MCP73861 datasheet(13/26 Pages) MICROCHIP

13 / 26 page

 2004 Microchip Technology Inc.

DS21893A-page 13

MCP73861/2

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 opera-

tional

flow

algorithm

from

charge

initiation

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 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 undervoltage lockout stop threshold

for at least one clock period to be considered valid.

After 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 volt-

age 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 volt-

age 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 volt-

age (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 regula-

tion value based on the state of the VSET. With VSET

tied to VSS, the MCP73861 and MCP73862 regulate to

4.1V and 8.2V, respectively. With VSET tied to VDD, the

MCP73861 and MCP73862 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 phase. 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 tem-

perature 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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