Datasheet

MCP73811/2
DS22036B-page 12 © 2007 Microchip Technology Inc.
5.0 DETAILED DESCRIPTION
5.1 Analog Circuitry
5.1.1 BATTERY MANAGEMENT INPUT
SUPPLY (V
DD
)
The V
DD
input is the input supply to the MCP73811/2.
The MCP73811/2 automatically enters a Power-down
mode if the voltage on the V
DD
input falls to within
+50 mV of the battery voltage. This feature prevents
draining the battery pack when the V
DD
supply is not
present.
5.1.2 MCP73812 CURRENT REGULATION
SET (PROG)
For the MCP73812, the charge current regulation can
be scaled by placing a programming resistor (R
PROG
)
from the PROG input to V
SS
. The program resistor and
the charge current are calculated using the following
equation:
EQUATION 5-1:
5.1.3 BATTERY CHARGE CONTROL
OUTPUT (V
BAT
)
The battery charge control output is the drain terminal
of an internal P-channel MOSFET. The MCP73811/2
provides constant current and voltage regulation to the
battery pack by controlling this MOSFET in the linear
region. The battery charge control output should be
connected to the positive terminal of the battery pack.
5.2 Digital Circuitry
5.2.1 CHARGE ENABLE (CE)
The charge enable input pin (CE) can be used to
terminate a charge at any time during the charge cycle,
as well as to initiate a charge cycle or initiate a recharge
cycle.
Driving the input to a logic High enables the device.
Driving the input to a logic Low disables the device and
terminates a charge cycle. When disabled, the device’s
supply current is reduced to 50 µA, typically.
5.2.2 MCP73811 CURRENT REGULATION
SELECT (PROG)
For the MCP73811, driving the PROG input to a logic
Low selects the low charge current setting (85 mA).
Driving the PROG input to a logic High selects the high
charge current setting (450 mA).
I
REG
1000V
R
PROG
-----------------=
Where:
R
PROG
= kilo-ohms
I
REG
= milliamperes