MCP73837-AMISLASHMF datasheet(17/36 Pages) MICROCHIP

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DS20002071C-page 17

MCP73837/8

4.5.1

TIMER EXPIRED DURING

CONSTANT CURRENT – FAST

CHARGE MODE

If the internal timer expires before the recharge voltage

threshold is reached, a timer fault is indicated and the

charge cycle terminates. The MCP73837/8 remains in

this condition until the battery is removed, the input

battery is removed or the PROG1/2 pin is opened. If the

battery is removed or the PROG1/2 pin is opened, the

MCP73837/8 enters the Stand-by mode where it

remains until a battery is reinserted or the PROG1/2 pin

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 begins.

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,

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 ter-

mination. The percentage or ratio of the current is fac-

tory set. The timer period is factory set and can be

disabled. Refer to Section 1.0 “Electrical Characteris-

tics” 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 6.1.1.3

“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

constantly

charging a Li-Ion battery in order to pro-

long its life, while keeping its capacity at a

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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