Datasheet

 2008-2013 Microchip Technology Inc. DS20002090C-page 17
MCP73871
3.0 PIN DESCRIPTION
The descriptions of the pins are listed in Table 3-1.
3.1 Power Supply Input (IN)
A supply voltage of V
REG
+ 0.3V to 6V is
recommended. Bypass to V
SS
with a minimum of
4.7 μF.
3.2 System Output Terminal (OUT)
The MCP73871 device powers the system via output
terminals while independently charging the battery.
This feature reduces the charge and discharge cycles
on the battery, allowing proper charge termination and
the system to run with an absent or defective battery
pack. It also gives the system priority on input power,
allowing the system to power up with deeply depleted
battery packs. Bypass to V
SS
with a minimum of 4.7 μF
is recommended.
3.3 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. If possible, further demand from the system is
supported by the battery. To enable this feature, simply
supply 1.23V or greater to the VPCC pin. This feature
can be disabled by connecting the VPCC pin to IN.
For example, a system is designed with a 5.5V rated
DC power supply with ±0.5V tolerance. The worst
condition of 5V is selected, which is used to calculate
the VPCC supply voltage with divider.
TABLE 3-1: PIN FUNCTION TABLE
Pin
Number
Symbol I/O Function
1, 20 OUT O System Output Terminal
2 VPCC I Voltage proportional charge control
3 SEL I Input type selection (Low for USB port, High for AC-DC adapter)
4 PROG2 I USB port input current limit selection when SEL = Low
(Low = 100 mA, High = 500 mA)
5 THERM I/O Thermistor monitoring input and bias current
6
PG O Power-Good Status Output (Open-Drain)
7 STAT2 O Charge Status Output 2 (Open-Drain)
8 STAT1/
LBO O Charge Status Output 1 (Open-Drain). Low battery output indicator when
V
BAT
> V
IN
9 TE I Timer Enable; Enables Safety Timer when active Low
10, 11, EP V
SS
— Battery Management 0V Reference. EP (Exposed Thermal Pad).
There is an internal electrical connection between the exposed thermal pad and
V
SS
. The EP must be connected to the same potential as the V
SS
pin on the
Printed Circuit Board (PCB)
12 PROG3 I/O Termination set point for both AC-DC adapter and USB port
13 PROG1 I/O Fast charge current regulation setting with SEL = High. Preconditioning set point
for both USB port and AC-DC adapter
14, 15 V
BAT
I/O Battery Positive Input and Output connection
16 V
BAT_SENSE
I/O Battery Voltage Sense
17 CE I Device Charge Enable; Enabled when CE = High
18, 19 IN I Power Supply Input
Legend: I = Input, O = Output, I/O = Input/Output
Note: To ensure proper operation, the input pins must not allow floating and should always tie to either High or
Low.