MCP73871 datasheet(22/38 Pages) MICROCHIP

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MCP73871

DS22090B-page 22

4.12

Voltage Proportional Charge

Control (VPCC)

If the voltage on the IN pin drops to a preset value,

determined by the threshold established at the VPCC

input, due to a limited amount of input current or input

source impedance, then the battery charging current is

reduced.

The

VPCC

control

tries

reach

steady-state condition where the system load has

priority and the battery is charged with the remaining

current. Therefore, if the system demands more

current than the input can provide, the ideal diode will

become forward biased and the battery is able to

supplement the input current to the system load.

The VPCC sustains the system load as its highest

priority. It does this by reducing the noncritical charge

current while maintaining the maximum power output of

the adapter. Further demand from the system is

supported by the battery, if possible.

The VPCC feature functions identically for USB port or

ac-dc adapter inputs. This feature can be disabled by

connecting the VPCC to IN pin.

4.13

Input Current Limit Control (ICLC)

If the input current threshold is reached, then the

battery charging current is reduced. The ICLC tries to

reach a steady-state condition where the system load

has priority and the battery is charged with the

remaining current. No active control limits the current

to the system. Therefore, if the system demands more

current than the input can provide or the input ICLC is

reached, the ideal diode will become forward biased

and the battery is able to supplement the input current

to the system load.

The ICLC sustains the system load as its highest

priority. This is done by reducing the non-critical charge

current while adhering to the current limits governed by

the USB specification or the maximum ac-dc adapter

current supported. Further demand from the system is

supported by the battery, if possible.

FIGURE 4-4:

Input Current Limit Control -

USB Port.

-200

-100

100

200

300

400

500

600

700

100 200 300 400 500 600 700

Load Current (mA)

Input Current

Battery Current

Load Current

Ideal

Diode

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