Datasheet

© 2007-2011 Microchip Technology Inc. DS22071B-page 17
MCP73837/8
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 ensues.
4.6 Constant Voltage Mode
When the voltage at the V
BAT
pin reaches the
regulation voltage, V
REG
, 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 Character-
istics” 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 V
BAT
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 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.
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 a
healthy level.
0
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)
Charge Current (mA)
R
PROG
= 1 kΩ