Datasheet

MCP73811/2
DS22036B-page 10 © 2007 Microchip Technology Inc.
4.0 DEVICE OVERVIEW
The MCP73811/2 are simple, but fully integrated linear
charge management controllers. Figure 4-1 depicts the
operational flow algorithm.
FIGURE 4-1: Flow Chart.
4.1 Undervoltage Lockout (UVLO)
The MCP73811/2 does not have an internal under
voltage lockout (UVLO) circuit.
4.2 Charge Qualification
When the input power is applied, the input supply must
rise 150 mV above the battery voltage before the
MCP73811/2 becomes operational.
The automatic power down circuit places the device in
a shutdown mode if the input supply falls to within
+50 mV of the battery voltage.
The automatic circuit is always active. Whenever the
input supply is within +50 mV of the voltage at the V
BAT
pin, the MCP73811/2 is placed in a shutdown mode.
During power down condition, the battery reverse dis-
charge current is less than 2 µA.
For a charge cycle to begin, the automatic power down
conditions must be met and the charge enable input
must be above the input high threshold.
4.3 PRECONDITIONING
The MCP73811/2 does not support preconditioning of
deeply depleted cells.
4.4 Constant Current MODE - Fast
Charge
During the constant current mode, the selected
(MCP73811) or programmed (MCP73812) charge
current is supplied to the battery or load.
For the MCP73812, the charge current is established
using a single resistor from PROG to V
SS
. The program
resistor and the charge current are calculated using the
following equation:
EQUATION 4-1:
Constant current mode is maintained until the voltage
at the V
BAT
pin reaches the regulation voltage, V
REG
.
4.5 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
with a tolerance of ±1.0%.
4.6 Charge Termination
The charge cycle is terminated by removing the battery
from the charger, removing input power, or driving the
charge enable input (CE) to a logic Low. An automatic
charge termination method is not implemented.
4.7 Automatic Recharge
The MCP73811/2 does not support automatic recharge
cycles since automatic charge termination has not
been implemented. In essence, the MCP73811/2 is
always in a charge cycle whenever the qualification
parameters have been met.
SHUTDOWN MODE*
V
DD
< V
PD
CONSTANT CURRENT
MODE
Charge Current = I
REG
CONSTANT VOLTAGE
MODE
Charge Voltage = V
REG
* Continuously
Monitored
V
BAT
= V
REG
STANDBY MODE*
CE = Low
V
BAT
< V
REG
I
REG
1000V
R
PROG
-----------------=
Where:
R
PROG
= kilo-ohms
I
REG
= milliamperes