ISL6293_06 Datasheet, PDF (7/8 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger Accepting Two Power Sources

ISL6293
Description
The ISL6293 is designed for a single-cell Li-ion or Li-polymer
battery charging circuit that accepts both a USB port and a
desktop cradle as its power source. The charge current from
each power source is independently programmable but only
one of the two sources charges the battery. The following
describes the operation of the charger.
Input Auto Selection
When both input sources are present, the charger selects
only one power source to charge the battery. When the
CRDL input is higher than both the POR threshold and the
battery voltage, CRDL is selected as the power source.
Otherwise the USB input is selected. If the CRDL input
voltage is below the battery voltage but the USB input
voltage is higher than the battery voltage, then the USB input
is used to charge the battery. The control circuit always
breaks both internal power devices before switching in one
power source to avoid any simultaneous conduction of both
power MOSFETs.
When the BAT pin voltage is below 1.7V, the charger selects
the CRDL input as the power source. Hence, if the USB
input is powered, the charger will not charge the battery.
USB Charge Current
When the USB port is selected as the power source, the
charge current is programmed by the logic input USBP pin.
With the R_IUSB selected at 80kΩ, when the USBP is driven
to logic LOW, the charge current is set to 90mA. When the
USBP is driven to logic HIGH, the charge current is set to
450mA. The USBP is equivalent to a logic LOW when left
floating. Typically the P-channel MOSFET for the USB input
has an r_DS(ON) of 700mΩ at room temperature, thus with a
500mA charge current, the typical head room is 350mV. If
the input voltage drops to a level that the voltage different
between the USB pin and the BAT pin is less than 350mV,
the r_DS(ON) becomes a limiting factor of the charge current
and the charge current drops out the constant current
regulation.
Cradle Charge Current
The cradle charge current is programmed with the external
resistor connected between the ICDL pin and the GND pin.
The current can be calculated with the equation given in the
ICDL pin description. The typical r_DS(ON) value of the P-
channel MOSFET for the CRDL input is 700mΩ at room
temperature, thus when the head room between the input
and output voltages is small, the actual charge current,
similar to the USB case, could be limited by the r_DS(ON). On
the other hand, if the head room between the input and
output voltages is large, the charge current maybe limited by
the thermal foldback threshold due to the increased power
dissipation.
Floating Charge Voltage
The floating voltage during the constant voltage phase is
4.2V. The floating voltage has an 1% accuracy over the
ambient temperature range of -40°C to 70°C.
Trickle Charge Current
When the battery voltage is below the minimum battery
voltage V_MIN given in the electrical specification, the charger
operates in a trickle/preconditioning mode. If power comes
from the cradle, the trickle mode current is
I_TRICKLE=
-¹----^.-²----⁰---^V----
R_ICDL
⋅
100
(A)
The trickle current is 45mA if the power comes from the USB
port with R_IUSB = 80kΩ.
End-of-Charge Indication
The CHG pin outputs a logic HIGH by turning off the internal
open-drain MOSFET when the charge current falls below
8% of the constant current mode current for the cradle input
or 10% for the USB input when R_IUSB is 80kΩ. The charger,
however, does not turn off as long as an input power source
is attached.
Power Presence Indication
When either the USB or the cradle input voltage is above the
POR level, the PPR pin outputs a logic LOW signal to
indicate the presence of input power.
7
FN9180.1
January 4, 2006