SC801
POWER MANAGEMENT
Applications Information
Monitor Mode
Pre-Charge Mode
In the monitor mode the voltage of the battery will be
monitored against the programmed voltage. This will oc-
cur after a battery has been fully charged and the device
has shut off. If the voltage of the battery falls below the
recharge threshold (specified at 200mV) the charger will
activate and charge the battery to its programmed volt-
age. This means that it will enter the full charging se-
quence from fast-charge to terminating the charging cycle
when the programmed termination current is reached.
The maximum current drain of the battery during moni-
tor mode will be no more than 1uA over temperature.
Pre-charge mode is automatically enabled whenever the
battery voltage is below 2.8V. It is primarily used to limit
the power dissipation of the battery and the SC801 de-
vice whenever the battery is undercharged. As the bat-
tery begins to charge in this mode, the voltage of the
battery will rise and when the 2.8V limit is reached, the
SC801 will switch to the fast charge mode. The pre-
charge current value is selected by the termination re-
sistor on the ITERM pin. The maximum range of the pre-
charge current is from 10mA to 125mA. Whenever the
charger is in pre-charge or fast-charge the status LED
will light indicating that the battery is being charged. The
equation to select the pre-charge current is given by:
LDO Mode
One of the nice features of the SC801 is its ability to
work with or without a battery. If the battery is not in
place the device can enter the LDO mode. In this mode
the SC801 will act like a low dropout regulator. The out-
put voltage is set to 4.1V, 4.2V or externally set by a
2.8
PCI=
• 88
R
TERM
Fast-Charge Mode
The fast-charge mode exists while the battery voltage is resistor divider. See the section titled Configuring the
above 2.8V and the battery is not fully charged. The fast- Output Voltage to the Battery for setting an output volt-
charge current can be set to a maximum of 1.5A and is age other than 4.1V or 4.2V. The input pin BIP (Battery
selected by the program resistor on the IPRGM pin. In In Place) is used to switch the SC801 from charger mode
fact, the voltage on this pin will represent the current to LDO mode. If this pin is logic high the device will be in
through the battery enabling a microprocessor or ana- charger mode, if it is logic low it will be in the LDO mode.
log-to-digital converter (ADC), to monitor battery current During LDO mode the device will regulate the output volt-
by sensing the voltage on the IPRGM pin. The equation age with a current limit set by the resistor tied to the
to set the fast-charge current is given by:
IPRGM pin. The BIP pin can be tied to the CP pin to place
the device in charge mode whenever the adaptor is in
place. The maximum voltage on the BIP input pin is 6V,
so do not tie it to the VCC input since this voltage can
exceed 6V in some conditions. The BIP pin should never
be left floating, but instead, should be tied through pull-
up/pull-down resistors when connected to a high imped-
ance control pin, otherwise it can be connected directly
to the CP pin or GND. The equation for setting the cur-
rent limit in the LDO mode will be:
1.5
FCI=
• 1000
R
PRGM
Note that for a given program resistor the current through
the battery 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 4.1V,
4.2V or externally set voltage, the device will transition
from a constant current source to a constant voltage
source, as the current through the battery begins to de-
crease while the voltage remains constant. During this
time when the current falls below the programmed ter- LED Flags
1.5
ILDO=
• 1000
R
PRGM
mination current set by the termination resistor on the There are three LED drivers on the SC801: OVP (Over
ITERM pin, the SC801 will turn off and the end of charge Voltage), STAT (Status) and CP (Charger Present). Each
will be indicated by the status LED turning off. The equa- output can drive an LED directly without a current limit
tion to set the termination current is given by:
resistor. In addition, each output can be monitored by a
microprocessor for change in their status. The table above
defines each LED output.
1.5
ITERM=
• 88
R
TERM
2002 Semtech Corp.
6
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
