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11
FN9252.0
March 20, 2007
Remote Battery Voltage Sensing
In the ISL9205A, ISL9205B and ISL9205C versions, a Kelvin
sense pin is provided for battery terminal voltage monitoring.
Thus, the IR drop due to the connection leads and PCB
traces can be eliminated, resulting a more accurate battery
voltage monitoring, especially when the battery is located at
a significant distance away from the ISL9205. If remote
sensing is not needed, the VSEN pin can be connected to
VBAT at the IC.
Applications Information
PCB Layout Guidance
The ISL9205 uses a thermally-enhanced DFN package that
has an exposed thermal pad at the bottom side of the
package. The layout should connect as much as possible to
copper on the exposed pad. Typically the component layer is
more effective in dissipating heat. The thermal impedance
can be further reduced by using other layers of copper
connecting to the exposed pad through a thermal via array. A
minimum of four (4) such thermal vias are recommended.
Each thermal via is recommended to have 0.3mm diameter
and 0.7mm distance from other thermal vias.
Stability Consideration
The ISL9205 should behave like a current and thermal
limited linear regulator. The charger operation is stable with
an output ceramic decoupling capacitor in the range of 1μF
to 200μF, with or without a battery connected.
Input Bypass Capacitor
Due to the inductance of the power leads of the wall adapter
or USB source, the input capacitor type must be properly
selected to prevent high voltage transient during a hot-plug
event. A tantalum capacitor is a good choice for its high
ESR, providing damping to the voltage transient. Multi-layer
ceramic capacitors, however, have a very low ESR and
hence when chosen as input capacitor, a 1
Ω
series resistor
must be used, as shown in the “Typical Applications” on
page 4, to provide adequate damping.
2.8V Bias Voltage
The ISL9205 provides a 2.8V voltage for biasing the internal
control and logic circuit. This voltage is also available for
external circuits such as the NTC thermistor circuit. The
maximum allowed external load is 2mA. A bypass capacitor
is needed at this pin for best performace. It is recommentded
to use a minimum 1.0
μ
F, X5R type of ceramic capacitor.
State Machine Diagram
The state machine diagram is shown in Figure 14. The
diagram starts with the Power-Off state. When the input
voltage rises above the POR threshold, the charger resets
itself. Then, if the charger is disabled, the charger stays in
the Charger Disabled state. If the charger is enabled, the
trickle charge starts. Anytime when entering the trickle
charge state, the internal TIMEOUT timer is reset. There are
two paths to exit the trickle charge, one is when the battery
voltage rises above the preconditioning charge threshold
within the 1/8 TIMEOUT interval and the other is when the
1/8 TIMEOUT interval has been elapsed before reaching the
preconditioning charge voltage threshold. When TIMEOUT
fault occurs, the charger enters the TIMEOUT fault state.
There are only two ways to exit the TIMEOUT fault state, by
toggling the EN input or re-cycling the input power. If the
charger finishes the trickle charger before the 1/8 TIMEOUT
limit, it moves to the fast charge state. When entering the
fast charge state, the TIMEOUT timer is reset as well. If the
charger hits EOC conditions before the TIMEOUT, the
charger enters Charge Compete state. The charger stays on
but the STATUS indicates EOC condition, until the TIMEOUT
(starting from entering the fast charge state) is reached then
the charger moves to the Inhibit state. In the Inhibit state, the
charger is off and the EOC condition continues to be
indicated.
ISL9205