MCP73861/2/3/4
4.0
DEVICE OVERVIEW
The MCP7386X family of devices are highly advanced
linear charge management controllers. Refer to the
functional block diagram. Figure 4-2 depicts the
operational flow algorithm from charge initiation to
completion and automatic recharge.
MCP73862/4 regulate to 4.1V and 8.2V, respectively.
With VSET tied to VDD
, the MCP73861/3 and
MCP73862/4 regulate to 4.2V and 8.4V, respectively.
4.4
Charge Cycle Completion and
Automatic Re-Charge
4.1
Charge Qualification and
Preconditioning
The MCP7386X monitors the charging current during
the Constant-voltage regulation mode. The charge
cycle is considered complete when the charge current
has diminished below approximately 8% of the
regulation current (IREG), or the elapsed timer has
expired.
Upon insertion of a battery, or application of an external
supply, the MCP7386X family of devices automatically
performs a series of safety checks to qualify the
charge. The input source voltage must be above the
Undervoltage Lockout (UVLO) threshold, the enable
pin must be above the logic-high level and the cell
temperature must be within the upper and lower
thresholds. The qualification parameters are
continuously monitored. Deviation beyond the limits
automatically suspends or terminates the charge cycle.
The input voltage must deviate below the UVLO stop
threshold for at least one clock period to be considered
valid.
The MCP7386X automatically begins a new charge
cycle when the battery voltage falls below the recharge
threshold (VRTH), assuming all the qualification
parameters are met.
4.5
Thermal Regulation
The MCP7386X family limits the charge current based
on the die temperature. Thermal regulation optimizes
the charge cycle time while maintaining device reliabil-
ity. If thermal regulation is entered, the timer is automat-
ically slowed down to ensure that a charge cycle will
not terminate prematurely. Figure 4-1 depicts the
thermal regulation profile.
Once the qualification parameters have been met, the
MCP7386X 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 (VPTH),
the MCP7386X preconditions the battery with a trickle-
charge. The preconditioning current is set to approxi-
mately 10% of the fast charge regulation current. The
preconditioning trickle-charge safely replenishes
deeply depleted cells and minimizes heat dissipation
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.
1400
1200
1000
800
Maximum
Minimum
600
400
200
0
4.2
Constant Current Regulation –
Fast Charge
0
20
40
60
80
100
120
140
Die Temperature (° C)
Preconditioning ends, and fast charging begins, when
the battery voltage exceeds the preconditioning thresh-
old. Fast charge regulates to a constant current (IREG),
which is set via an external resistor connected to the
PROG pin. Fast charge continues until the battery
voltage reaches the regulation voltage (VREG), or the
fast charge timer expires; in which case, a fault is
indicated and the charge cycle is terminated.
FIGURE 4-1:
Current vs. Die Temperature.
Typical Maximum Charge
4.6
Thermal Shutdown
The MCP7386X family suspends charge if the die
temperature exceeds 155°C. Charging will resume
when the die temperature has cooled by approximately
10°C. The thermal shutdown is a secondary safety
feature in the event that there is a failure within the
thermal regulation circuitry.
4.3
Constant Voltage Regulation
When the battery voltage reaches the regulation
voltage (VREG), constant voltage regulation begins.
The MCP7386X monitors the battery voltage at the
VBAT pin. This input is tied directly to the positive
terminal of the battery. The MCP7386X selects the
voltage regulation value based on the state of VSET
.
With VSET tied to VSS the MCP73861/3 and
,
© 2005 Microchip Technology Inc.
DS21893C-page 13
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