MCP73871 Microchip Technology, MCP73871 Datasheet - Page 23

• Manufacturer Part Number: MCP73871
• Description: Stand-Alone System Load Sharing and Li-Ion / Li-Polymer Battery Charge Management Controller
• Manufacturer: Microchip Technology

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5.0
5.1
5.1.1
The V
device. The MCP73871 device can be supplied by
either AC Adapter (V
pin. The MCP73871 device automatically powers the
system with the Li-Ion battery when the V
present.
5.1.2
For the MCP73871 device, the charge current
regulation can be scaled by placing a programming
resistor (R
program resistor and the charge current are calculated
using the following equation:
EQUATION 5-1:
The fast charge current is set for maximum charge
current from ac-dc adapter and USB port. The
preconditioning current is 10% (0.1C) to the fast
charge current.
5.1.3
The battery charge control output is the drain terminal
of an internal P-channel MOSFET. The MCP73871
device
regulation to the battery pack by controlling this
MOSFET in the linear region. The battery charge
control output should be connected to the positive
terminal of the battery pack.
5.1.4
The MCP73871 device continuously monitors battery
temperature during a charge cycle by measuring the
voltage between the THERM and V
50 µA current source provides the bias for most
common
(NTC) or positive-temperature coefficient (PTC)
thermistors.The current source is controlled, avoiding
measurement sensitivity to fluctuations in the supply
voltage (V
voltage at the THERM pin to factory set thresholds of
© 2009 Microchip Technology Inc.
Where:
R
PROG
I
REG
IN
DETAILED DESCRIPTION
Analog Circuitry
provides
input is the input supply to the MCP73871
DD
PROG1
10 kΩ
LOAD SHARING AND LI-ION
BATTERY MANAGEMENT INPUT
SUPPLY (V
FAST CHARGE CURRENT
REGULATION SET (PROG1)
BATTERY CHARGE CONTROL
OUTPUT (V
TEMPERATURE QUALIFICATION
(THERM)
). The MCP73871 device compares the
=
=
) from the PROG1 pin to V
I
REG
kilo-ohms (kΩ)
milliampere (mA)
negative-temperature
constant
AC
) or USB Port (V
=
IN
BAT
)
------------------- -
R
1000V
PROG1
)
current
SS
pins. An internal
USB
and
IN
input is not
) with SEL
coefficient
SS
voltage
. The
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 charge by turning off
the pass transistor and holding the timer value. The
charge cycle resumes when the voltage at the THERM
pin returns to the normal range.
If temperature monitoring is not required, place a
standard 10 kΩ resistor from THERM to V
5.2
5.2.1
The charge status outputs have two different states:
Low (L), and High Impedance (Hi-Z). The charge status
outputs can be used to illuminate LEDs. Optionally, the
charge status outputs can be used as an interface to a
host microcontroller.
the status outputs during a charge cycle.
TABLE 5-1:
5.2.2
With the SEL input Low, the MCP73871 device is
designed to provide system power and Li-Ion battery
charging from a USB input while adhering to the current
limits governed by the USB specification. The host
microcontroller has the option selecting either a
100 mA (L) or a 500 mA (H) current limit based on the
PROG2 input. With the SEL input High, the MCP73871
device limits the input current to 1.8A. The
programmed charge current is established using a
single resistor from PROG1 to V
High.
Shutdown (V
Shutdown (V
Preconditioning
Constant Current
Constant Voltage
Charge Complete - Standby
Temperature Fault
Timer Fault
Low Battery Output
No Battery Present
No Input Power Present
CHARGE CYCLE STATE
Digital Circuitry
STATUS INDICATORS AND
POWER-GOOD (PG)
AC-DC ADAPTER AND USB PORT
POWER SOURCE REGULATION
SELECT (SEL)
DD
DD
= V
= IN)
STATUS OUTPUTS
BAT
Table 5-1
)
MCP73871
STAT1
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
summarizes the state of
L
L
L
L
L
L
SS
when driving SEL
DS22090B-page 23
STAT2
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
Hi-Z
L
L
L
SS
.
Hi-Z
Hi-Z
Hi-Z
PG
L
L
L
L
L
L
L
L