Data Sheet

MCP73831
DS21984A-page 12 © 2005 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 MCP73831.
The MCP73831 automatically enters a Power-Down
mode if the voltage on the V
DD
input falls below the
UVLO voltage (V
STOP
). This feature prevents draining
the battery pack when the V
DD
supply is not present.
5.1.2 CURRENT REGULATION SET
(PROG)
Fast 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:
The preconditioning trickle charge current and the
charge termination current are ratiometric to the fast
charge current based on the selected device options.
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 MCP73831
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 STATUS INDICATOR (STAT)
The charge status output has three different states:
High (H), Low (L), and High-Impedance (Hi-Z). The
charge status output can be used to illuminate 1, 2, or
tricolor LEDs. Optionally, the charge status output can
be used as an interface to a host microcontroller.
Table 5-1 summarize the state of the status output
during a charge cycle.
5.2.2 DEVICE DISABLE (PROG)
The current regulation set input pin (PROG) 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.
Placing a programming resistor from the PROG input to
V
SS
enables the device. Allowing the PROG input to
float or by applying a logic-high input signal, disables
the device and terminates a charge cycle. When
disabled, the device’s supply current is reduced to
25 μA, typically.
I
REG
1000V
R
PROG
-----------------
=
Where:
R
PROG
=kOhms
I
REG
= milliampere
TABLE 5-1: STATUS OUTPUT
Charge Cycle State STAT1
Shutdown Hi-Z
No Battery Present Hi-Z
Preconditioning L
Constant-Current Fast Charge L
Constant Voltage L
Charge Complete – Standby H