2002-2013 Microchip Technology Inc. DS21705B-page 9
MCP73826
4.0 DEVICE OVERVIEW
The MCP73826 is a linear charge management con-
troller. Refer to the functional block diagram on page 2
and the typical application circuit, Figure 6-1.
4.1 Charge Qualification and
Preconditioning
Upon insertion of a battery or application of an external
supply, the MCP73826 verifies the state of the SHDN
pin. The SHDN pin must be above the logic high level.
If the SHDN
pin is above the logic high level, the
MCP73826 initiates a charge cycle. If the cell is below
the preconditioning threshold, 2.4V typically, the
MCP73826 preconditions the cell with a scaled back
current. The preconditioning current is set to approxi-
mately 43% of the fast charge peak current. The pre-
conditioning safely replenishes deeply depleted cells
and minimizes heat dissipation in the external pass
transistor during the initial charge cycle.
4.2 Controlled Current Regulation - Fast
Charge
Preconditioning ends and fast charging begins when
the cell voltage exceeds the preconditioning threshold.
Fast charge utilizes a foldback current scheme based
on the voltage at the V
SNS
input developed by the drop
across an external sense resistor, R
SENSE
, and the out-
put voltage,
V
BAT
. Fast charge continues until the cell
voltage reaches the regulation voltage, V
REG
.
4.3 Constant Voltage Regulation
When the cell voltage reaches the regulation voltage,
V
REG
, constant voltage regulation begins. The
MCP73826 monitors the cell voltage at the
V
BAT
pin.
This input is tied directly to the positive terminal of the
battery. The MCP73826 is offered in two fixed-voltage
versions for battery packs with either coke or graphite
anodes: 4.1V (MCP73826-4.1) and 4.2V
(MCP73826-4.2).
4.4 Charge Cycle Completion
The charge cycle can be terminated by a host micro-
controller after an elapsed time from the start of the
charge cycle. The charge is terminated by pulling the
shutdown pin, SHDN
, to a logic Low level.
