MCP73837AMIMF datasheet(17/30 Pages) MICROCHIP

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DS22071A-page 17

MCP73837/8

is reconnected. If the input power is removed, the

MCP73837/8 is in Shutdown. When the input power is

reapplied, a normal start-up sequence ensues.

4.6

Constant Voltage Mode

When the voltage at the VBAT pin reaches the

regulation voltage, VREG, constant voltage regulation

begins. The regulation voltage is factory set to 4.20V,

4.35V, 4.40V, or 4.5V with a tolerance of ± 0.5%.

4.7

Charge Termination

The charge cycle is terminated when, during constant

voltage mode, the average charge current diminishes

below a percentage of the programmed charge current

(established with the value of the resistor connected to

the PROG pin) or the internal timer has expired. A 1 ms

filter time on the termination comparator ensures that

transient load conditions do not result in premature

charge cycle termination. The percentage or ratio of the

current is factory set. The timer period is factory set and

can be disabled. Refer to Section 1.0 “Electrical

Characteristics” for charge termination current ratio

and timer period options.

The charge current is latched off and the MCP73837/8

enters a charge complete mode.

4.8

Automatic Recharge

The MCP73837/8 continuously monitors the voltage at

the VBAT pin in the charge complete mode. If the

voltage drops below the recharge threshold, another

charge cycle begins and current is once again supplied

to the battery or load. The recharge threshold is factory

set. Refer to Section 1.0 “Electrical Characteristics”

for recharge threshold options.

4.9

Thermal Regulation

The MCP73837/8 limits the charge current based on

the die temperature. The thermal regulation optimizes

the charge cycle time while maintaining device

reliability. Figure 4-2 depicts the thermal regulation for

the MCP73837/8. Refer to Section 1.0 “Electrical

Characteristics” for thermal package resistances and

Section 6.1.1.2

“Thermal

Considerations”

for

calculating power dissipation.

FIGURE 4-2:

Thermal Regulation.

4.10

Thermal Shutdown

The MCP73837/8 suspends charge if the die

temperature exceeds 150°C. Charging will resume

when

the

die

temperature

has

cooled

approximately 10°C. The thermal shutdown is a

secondary safety feature in the event that there is a

failure within the thermal regulation circuitry.

Note:

Charge

termination

and

automatic

recharge features avoid constant charging

Li-Ion batteries to prolong the life of Li-Ion

batteries while keeping their capacity at

healthy level.

100

200

300

400

500

600

700

800

900

1000

1100

1200

25 35 45 55 65 75 85 95 105 115 125 135 145 155

Junction Temperature (°C)

RPROG = 1 kΩ

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