MCP73871 datasheet(16/38 Pages) MICROCHIP

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MCP73871

DS22090B-page 16

The voltage divider equation is shown below:

The calculated R1 equals to 337.2 kΩ when 110 kΩ is

selected for R2. The 330 kΩ resistor is selected for R1

to build the voltage divider for VPCC.

FIGURE 3-1:

Voltage Divider Example.

3.4

Input Source Type Selection (SEL)

The input source type selection (SEL) pin is used to

select input power source for input current limit control

feature. With the SEL input High, the MCP73871

device is designed to provide a typical 1.65A to system

power and charge Li-Ion battery from a regular 5V wall

adapter. The MCP73871 device limits the input current

up to 1.8A. When SEL active Low, the input source is

designed to provide system power and Li-Ion battery

charging from a USB Port input while adhering to the

current limits governed by the USB specification.

3.5

Battery Management 0V Reference

(VSS)

Connect to negative terminal of battery, system load

and input supply.

3.6

Battery Charge Control Output

(VBAT)

Connect to positive terminal of Li-Ion / Li-Polymer

batteries. Bypass to VSS with a minimum of 4.7 µF to

ensure loop stability when the battery is disconnected.

3.7

Battery Voltage Sense

(VBAT_SENSE)

Connect to positive terminal of battery. A precision

internal voltage sense regulates the final voltage on

this pin to VREG.

3.8

Charge Current Regulation Set

(PROG1)

The maximum constant charge current is set by placing

a resistor from PROG1 to VSS. PROG1 sets the

maximum constant charge current for both ac-dc

adapter and USB port. However, the actual charge

current is based on input source type and system load

requirement.

3.9

USB-Port Current Regulation Set

(PROG2)

The MCP73871 device USB-Port current regulation set

input (PROG2) is a digital input selection. A logic Low

selects a 1 unit load input current from USB port

(100 mA); a logic High selects a 5 unit loads input

current from USB port (500 mA).

3.10

Charge Status Output 1 (STAT1)

STAT1 is an open-drain logic output for connection to

an LED for charge status indication. Alternatively, a

pull-up resistor can be applied for interfacing to a host

microcontroller. Refer to Table 5-1 for a summary of the

status output during a charge cycle.

3.11

Charge Status Output 2 (STAT2)

STAT2 is an open-drain logic output for connection to

an LED for charge status indication. Alternatively, a

pull-up resistor can be applied for interfacing to a host

microcontroller. Refer to Table 5-1 for a summary of the

status output during a charge cycle.

3.12

Power-Good (PG)

The power-good (PG) is an open-drain logic output for

input power supply indication. The PG output is low

whenever the input to the MCP73871 device is above

the UVLO threshold and greater than the battery

voltage. The PG output can be used as an indication to

the user via an illuminated LED or to the system via a

pull-up resistor for interfacing to a host microcontroller

that an input source other than the battery is supplying

power. Refer to Table 5-1 for a summary of the status

output during a charge cycle.

3.13

Low Battery Output (LBO)

STAT1 also serves as low battery output (LBO) if the

selected MCP73871 is equipped with this feature. It

reminds the system or end user when the Li-Ion battery

voltage level is low. The LBO feature enables when the

system is running from the Li-Ion batteries. The LBO

indicator can be used as an indication to the user via lit

up LED or to the system via a pull-up resistor for

interfacing to a host microcontroller that an input

source other than the battery is supplying power. Refer

to Table 5-1 for a summary of the status output during

a charge cycle.

VPCC

-------------------

⎝⎠

⎛⎞

1.23V

110k

Ω R

------------------------------

⎝⎠

⎛⎞

337.2k

330 k

110 k

VIN

VPCC

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