Datasheet

MCP73123/223
DS22191E-page 12  2009-2013 Microchip Technology Inc.
5.0 DETAILED DESCRIPTION
5.1 Undervoltage Lockout (UVLO)
An internal undervoltage lockout (UVLO) circuit
monitors the input voltage and keeps the charger in
Shutdown mode until the input supply rises above the
UVLO threshold. In the event a battery is present when
the input power is applied, the input supply must rise
approximately 150
mV above the battery voltage
before the MCP73123/223 becomes operational.
The UVLO circuit places the device in Shutdown mode
if the input supply falls to approximately 150
mV above
the battery voltage.The UVLO circuit is always active.
At any time, the input supply is below the UVLO
threshold or approximately 150
mV of the voltage at the
V
BAT
pin, the MCP73123/223 device is placed in a
Shutdown mode.
5.2 Overvoltage Protection (OVP)
An internal OVP circuit monitors the input voltage and
keeps the charger in Shutdown mode when the input
supply rises above the OVP threshold. The hysteresis
of OVP is approximately 150
mV for the MCP73123/
223 device.
The MCP73123/223 device is operational between
UVLO and OVP threshold. The OVP circuit is also
recognized as an overvoltage lockout (OVLO).
5.3 Charge Qualification
When the input power is applied, the input supply must
rise 150
mV above the battery voltage before the
MCP73123/223 becomes operational.
The automatic power down circuit places the device in
Shutdown mode if the input supply falls to within
+50
mV of the battery voltage.
The automatic circuit is always active. At any time the
input supply is within +50
mV of the voltage at the
V
BAT
pin, the MCP73123/223 is placed in a Shutdown
mode.
For a charge cycle to begin, the automatic power
down conditions must be met and the charge enable
input must be above the input high threshold.
5.3.1 BATTERY MANAGEMENT INPUT
SUPPLY (V
DD
)
The V
DD
input is the input supply to the MCP73123/
223. The
MCP73123/223 automatically enters a
Power-down mode if the voltage on the V
DD
input falls
to within +50
mV of the battery voltage. This feature
prevents draining the battery pack when the V
DD
supply is not present.
5.3.2 BATTERY CHARGE CONTROL
OUTPUT (V
BAT
)
The battery charge control output is the drain terminal
of an internal P-channel MOSFET. The MCP73123/223
provides constant current and voltage 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.
5.3.3 BATTERY DETECTION
The MCP73123/223 detects the battery presence by
monitoring the voltage at V
BAT
. The charge flow will
initiate when the voltage on V
BAT
is below the
V
RECHARGE
threshold. Refer to the Section 1.0,
"Electrical Characteristics", for V
RECHARGE
values.
When V
BAT
> V
REG
+ Hysteresis, the charge will be
suspended or not started, depending on the current
charge status, to prevent overcharging.
5.4 Preconditioning
If the voltage at the V
BAT
pin is less than the
preconditioning threshold, the MCP73123/223 device
enters a Preconditioning mode. The preconditioning
threshold is factory set. Refer to
Section 1.0,
"Electrical Characteristics", for preconditioning
threshold options.
In this mode, the MCP73123/223 device supplies 10%
of the fast charge current (established with the value of
the resistor connected to the PROG pin) to the battery.
When the voltage at the V
BAT
pin rises above the
preconditioning threshold, the MCP73123/223 device
enters the Constant Current (Fast Charge) mode.
5.4.1 TIMER EXPIRED DURING
PRECONDITIONING MODE
If the internal timer expires before the voltage threshold
is reached for Fast Charge mode, a timer fault is
indicated and the charge cycle terminates. The
MCP73123/223 device remains in this condition until
the battery is removed or input power is cycled. If the
battery is removed, the MCP73123/223 device enters
Standby mode, where it remains until a battery is rein
-
serted.
5.5 Constant Current Mode – Fast
Charge
During the Constant Current mode, the programmed
charge current is supplied to the battery or load.
Note: In order to extend the battery cycle life, the
charge will initiate only when battery
voltage is below 3.4V per cell.
Note: The MCP73123/223 also offers options
with no preconditioning.
Note: The typical preconditioning timer for
MCP73123/223 is 32 minutes. The
MCP73123/223 also offers options with no
preconditioning timer.