6
FN9212.1
January 3, 2006
USBON (Pin 7)
The USBON pin is a control input to turn off the USB charge
function if desired. Connect to LOW or leave floating to turn
off USB charge.
GND (Pin 8)
System ground.
ICDL (Pin 9)
The ICDL pin has two functions. The first function is to
program the cradle charge current during the constant-
current mode. The voltage of this pin is 1.22V during the
constant-current mode of the cradle charger. The constant-
current mode current is programmed by the following
equations:
where R
ICDL
is the resistor in connected to the ICDL pin
(see the Typical Application).
It is recommended that the charge current be programmed
in the range of 350mA to 650mA.
The second function of the ICDL pin is to monitor the actual
charge current. The voltage of this pin, V
ICDL
, is proportional
to the actual charge current, I
CHG
.
The cradle charge current should be programmed equal or
higher than the USB current; otherwise, the ICDL pin voltage
will be higher than 1.22V during the constant current mode
when the USB charger is working. The charger still works
properly but the accuracy of the current monitoring voltage
degrades and saturates at approximately 2.1V.
BAT (Pin 10)
Charger output pin. Connect this pin to the battery pack or
the battery cell. A 1µF or larger value ceramic capacitor is
recommended for decoupling. The charger relies on the
battery for stability so a battery should always be connected
to the BAT pin.
Description
The ISL6299A 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. While the charge
current from the USB input source is fixed at 380mA, the
charge current from the cradle input is programmable
between 0.1A and 1.0A by the resistor R
ICDL
. Similarly, the
end-of-charge current is fixed at typically 80mA for the USB
input and programmable for the cradle input by the resistor
R
IMIN
.
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 the POR threshold, 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 from one power source to the other
to avoid a cross conduction of both power MOSFETs.
USB Charge Current
When the USB port is selected as the power source, the
charge current enabled by the logic input at the USBON pin.
When the USBON is driven to logic LOW, the charger is
disabled. When the USBON is driven to logic HIGH, the
charge current is fixed at a typical value of 380mA. Thus for
the USB input, the USBON pin has a similar function as the
EN pin. The following table describes the USB charge
control by both the USBON pin and EN pin:
The USBON pin is equivalent to a logic LOW when left
floating. Typically the P-channel MOSFET for the USB input
has an r
DS(ON)
of 700m at room temperature. With a
380mA charge current, the typical head room is 260mV.
Thus, if the input voltage drops to a level that the voltage
difference between the USB pin and the BAT pin is less than
260mV, the r
DS(ON)
becomes a limiting factor of the charge
current; and the charger drops out the constant current
regulation.
Cradle Charge Current
The cradle charge current is enabled by the EN pin only, the
USBON pin has no control on the 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 one of the equations
given in the ICDL pin description. Two equations are used
for the cradle current calculation, each corresponds to a
different range of currents. The typical r
DS(ON)
of the
P-channel MOSFET for the CRDL input is 600m at room
temperature. 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 may be limited by the
thermal foldback threshold.
I
CLD
16685.5
R
ICDL
---------------------
0.026 0.1A I
CLD
0.7A–=
I
CDL
21242.1
R
ICDL
---------------------
0.188 0.7A I
CDL
1.1A–=
TABLE 1. USB CHARGE CONTROL
EN = LOW EN = HIGH
USBON = LOW Disabled Disabled
USBON = HIGH Enabled Disabled
ISL6299A
