6 2004 Semtech Corp. www.semtech.com
SC806
POWER MANAGEMENT
General Operation
The SC806 is configured based on the application for
Fast Charge and Termination current. A typical charging
cycle is described below. Details on alternate applica-
tions and output programmability are covered in the indi-
vidual sections.
The charging cycle begins when the adapter is plugged
in. The SC806 performs glitch filtering on the VCC input
and initiates a charge cycle when VCC > UVLO. At this
time, the CHRGB and CPB signals are active low turning
on the LEDs. If the battery voltage is less than 2.8V, the
SC806 will charge the output with the pre-charge cur-
rent. When the battery voltage exceeds 2.8V, the SC806
enters fast-charge or constant current (CC) mode. When
the battery voltage reaches its final value, the charger
enters the constant voltage (CV) mode. In this mode the
output voltage is held constant and the current de-
creases until the termination current level is reached.
At this point the charger enters monitor mode and the
CHRGB output is high impedance. The charger output
remains off in monitor mode until Vout drops by 100mV
and a new charge cycle is initiated.
Pre-Charge Mode
Pre-charge mode is automatically enabled whenever the
battery voltage is below 2.8V. It is used to limit the power
dissipation and precondition the battery for fast charg-
ing. The pre-charge current value is selected by the re-
sistor on the ITERM pin. The pre-charge current is pro-
grammable from 10mA to 125mA. The equation to se-
lect the pre-charge current is given by:
100
R
1.5
PCI
TERM
•
=
Fast-Charge Mode (CC)
The fast-charge or CC mode is active when the battery
voltage is above 2.8V and less than the 4.2V CV voltage
of the battery. The fast-charge current can be set to a
maximum of 1.0A and is selected by the program resis-
tor on the IPRGM pin. The voltage on this pin will repre-
sent the current through the battery enabling a micro-
processor to monitor battery current by sensing the volt-
age on the IPRGM pin.
The equation to set the fast-
charge current is given by:
1000
PRGM
R
1.5
FCI
•
=
Note that for a given program resistor the current through
the battery in CV mode can be determined by replacing
1.5 with the actual voltage on the IPRGM pin in the above
equation.
Termination Current
Once the battery reaches the program voltage of 4.2V
the device will transition from a constant current source
to a constant voltage source and the current through
the battery begins to decrease while the voltage remains
constant. When the current falls below the programmed
termination current set by the termination resistor on
the ITERM pin, the SC806 will transition the CHRGB pin
from low to high. The equation to set the termination
current is given by:
100
R
1.5
ITERM
TERM
•
=
Monitor Mode
When a charge cycle is completed, the SC806 output
turns off and the device enters monitor mode. If the
voltage of the battery falls below the recharge threshold
of 4.1V the charger will re-initiate a charge cycle. The
maximum current drain of the battery during monitor
mode will be no more than 1µA over temperature
NTC Input/NOBAT output
The SC806 detects the absence of the battery by moni-
toring the voltage on the NTC pin. When the NTC pin
voltage exceeds 90% of VCC the NOBAT output is driven
high. This function utilizes the standard NTC configura-
tion with the NTC component residing in the battery pack.
When the battery is removed the NTC element in the
resistor divider is missing and the NTC voltage is pulled
up to VCC.
The NOBAT output can be used to signal the system that
the battery has been removed or drive an external LED.
DIS Device Disable Interface
The DIS pin on the SC806 is used to shutdown the SC806
charger. This pin must be pulled low to enable the charger,
high will disable the charger (do not leave floating). The
CPB output indicating the adapter input status is active
regardless of the state of DIS.
