EUP8092X
Current-Limited Adapter
EN Input (Charge Enable)
Figure 25 shows the ideal current-voltage characteristics
of a current-limited adapter. VNL is the no-load adapter
output voltage and VFL is the full load voltage at the
current limit ILIM. Before its output current reaches the
limit ILIM, the adapter presents the characteristics of a
voltage source. The slope rO represents the output
resistance of the voltage supply. For a well regulated
supply, the output resistance can be very small, but some
adapters naturally have a certain amount of output
resistance.
The adapter is equivalent to a current source when
running in the constant-current region. Being a current
source, its output voltage is dependent on the load, which,
in this case, is the charger and the battery.
The EN digital input is used to disable or enable the
charge process. A high-level signal on this pin enables the
charge and a low-level signal disables the charge and
places the device in a low-power mode. A low-to-high
transition on this pin also resets all timers and timer fault
conditions.
Input and Output Capacitor Selection
Typically any type of capacitors can be used for the input
and the output. Use of a 0.47µF or higher value ceramic
capacitor for the input is recommended. When the battery
is attached to the charger, the output capacitor can be any
ceramic type with the value higher than 0.1µF. However,
if there is a chance the charger will be used as an LDO
linear regulator,
recommended.
a
10µF tantalum capacitor is
Figure 25. The Equivalent Circuit of the Charging System Working with Current Limited Adapter
DS8092X Ver 0.1 May 2008
14
EUTECH [ EUTECH MICROELECTRONICS INC ]
