MCP73871-1AAISLASHML datasheet(20/36 Pages) MICROCHIP

20 / 36 page

MCP73871

DS20002090F-page 20

 2008-2022 Microchip Technology Inc. and its subsidiaries

4.9

Thermal Regulation

The MCP73871 device limits the charge current based

on the die temperature. The thermal regulation

optimizes the charge cycle time while maintaining

device reliability. Figure 4-3 depicts the thermal

regulation for the MCP73871 device. Refer to

Section 1.0 “Electrical Characteristics” for thermal

package resistances and Section 6.1.1.2 “Thermal

Considerations” for calculating power dissipation.

FIGURE 4-3:

Thermal Regulation.

4.10

Thermal Shutdown

The MCP73871 device suspends charge if the die

temperature exceeds 150°C. Charging resumes 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.

4.11

Temperature Qualification

The MCP73871 device continuously monitors battery

temperature during a charge cycle by measuring the

voltage between the THERM and VSS pins. An internal

50 µA current source provides the bias for most

common 10 k

 NTC thermistors. The MCP73871

device compares the voltage at the THERM pin to

factory set thresholds of 1.24V and 0.25V, typically.

Once a voltage outside the thresholds is detected

during a charge cycle, the MCP73871 device

immediately

suspends

the

charge

cycle. The

MCP73871 device suspends charging by turning off

the charge pass transistor and holding the timer value.

The charge cycle resumes when the voltage at the

THERM pin returns to the normal range.

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, the battery charging current is

reduced. The VPCC control tries to reach a 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 becomes

forward-biased and the battery may 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 ICLC is

reached, the ideal diode becomes forward biased and

the battery may 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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