2003-2013 Microchip Technology Inc. DS21823D-page 11
MCP73841/2/3/4
4.0 DEVICE OVERVIEW
The MCP7384X family of devices are highly advanced,
linear charge management controllers. Figure 4-1
depicts the operational flow algorithm from charge
initiation to completion and automatic recharge.
4.1 Charge Qualification and
Preconditioning
Upon insertion of a battery or application of an external
supply, the MCP7384X family of devices automatically
perform a series of safety checks to qualify the charge.
The input source voltage must be above the
undervoltage lockout threshold, the enable pin must be
above the logic-high level and the cell temperature
monitor must be within the upper and lower thresholds.
The cell temperature monitor applies to both the
MCP73841 and MCP73842, with the qualification
parameters being continuously monitored. Deviation
beyond the limits automatically suspends or terminates
the charge cycle.
Once the qualification parameters have been met, the
MCP7384X initiates a charge cycle. The charge status
output is pulled low throughout the charge cycle (see
Table 5-1 for charge status outputs). If the battery
voltage is below the preconditioning threshold (V
PTH
),
the MCP7384X preconditions the battery with a trickle-
charge. The preconditioning current is set to
approximately 10% of the fast charge regulation
current. The preconditioning trickle-charge safely
replenishes deeply depleted cells and minimizes heat
dissipation in the external pass transistor during the
initial charge cycle. If the battery voltage has not
exceeded the preconditioning threshold before the
preconditioning timer has expired, a fault is indicated
and the charge cycle is terminated.
4.2 Constant-Current Regulation –
Fast Charge
Preconditioning ends and fast charging begins, when
the battery voltage exceeds the preconditioning
threshold. Fast charge regulates to a constant-current,
I
REG
, based on the supply voltage minus the voltage at
the SENSE input (V
FCS
) developed by the drop across
an external sense resistor (R
SENSE
). Fast charge
continues until the battery voltage reaches the
regulation voltage (V
REG
); or until the fast charge timer
expires. In this case, a fault is indicated and the charge
cycle is terminated.
4.3 Constant-Voltage Regulation
When the battery voltage reaches the regulation
voltage (V
REG
), constant-voltage regulation begins.
The MCP7384X monitors the battery voltage at the
V
BAT
pin. This input is tied directly to the positive
terminal of the battery. The MCP7384X is offered in
four fixed-voltage versions for single or dual series cell
battery packs with either coke or graphite anodes:
- 4.1V (MCP73841-4.1, MCP73843-4.1)
- 4.2V (MCP73841-4.2, MCP73843-4.2)
- 8.2V (MCP73842-8.2, MCP73844-8.2)
- 8.4V (MCP73842-8.4, MCP73844-8.4)
4.4 Charge Cycle Completion and
Automatic Re-Charge
The MCP7384X monitors the charging current during
the constant-voltage regulation phase. The charge
cycle is considered complete when the charge current
has diminished below approximately 7% of the
regulation current (I
REG
) or the elapsed timer has
expired.
The MCP7384X automatically begins a new charge
cycle when the battery voltage falls below the recharge
threshold (V
RTH
), assuming all the qualification
parameters are met.
