Datasheet
MCP73871
DS20002090C-page 18 2008-2013 Microchip Technology Inc.
The voltage divider equation is shown below:
EQUATION 3-1:
The calculated R
1
equals 337.2 k when 110 k is
selected for R
2
. The 330 k resistor is selected for R
1
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 capable of providing 1.65 (typical) total
amperes to be shared by the system load and Li-Ion
battery charging. 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
(V
SS
)
Connect to negative terminal of the battery, system
load and input supply.
3.6 Battery Charge Control Output
(V
BAT
)
Connect to positive terminal of the Li-Ion/Li-Polymer
battery. Bypass to V
SS
with a minimum of 4.7 μF to
ensure loop stability when the battery is disconnected.
3.7 Battery Voltage Sense
(V
BAT_SENSE
)
Connect to positive terminal of battery. A precision
internal voltage sense regulates the final voltage on
this pin to V
REG
.
3.8 Charge Current Regulation Set
(PROG1)
The maximum constant charge current is set by placing
a resistor from PROG1 to V
SS
. PROG1 sets the
maximum constant charge current for both AC-DC
adapter and USB port. However, the actual charge
current is based on the input source type and the
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 one unit load input current from the USB port
(100 mA) while a logic High selects a five unit load input
current from the 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 may be used with an LED or as
an interface to a host microcontroller to signal when an
input power source is supplying power to the system
and the battery. Refer to Table 5-1 for a summary of the
status output during a charge cycle.
V
VPCC
R
2
R
1
R
2
+
-------------------
V
IN
1.23V==
1.23V
110k
110k R
1
+
------------------------------
5V=
R
1
337.2k=
330 k
110 k
V
IN
VPCC