APL5501/2/3
Application Information
end-of-lifebattery voltage. Because theAPL5501/2/3
use a p-channel MOSFET pass transistor, the drop-
out voltage is a function of drain-to-source on-resis-
tance (RDS(ON)) multiplied by the load current.
Capacitor Selection and Regulator
Stability
The APL5501/2/3 use at least a 1uF capacitor on the
input, and this capacitor can be Aluminum, Tantalum
or Ceramic capacitor. The input capacitor with larger
value and lower ESR provides better PSRR and line-
transient response. The output capacitor also can use
Aluminum, Tantalum or Ceramic capacitor, and a mini-
mum value of 1uF and ESR above 0.06W is
recommended. The curve of the stable region in typi-
cal characteristics shows the appropriate output ca-
pacitor ESR for different loadcurrent stable operation.
A larger output capacitor can reduce noise and im-
prove load-transient response, stability, and PSRR.
Note that some ceramic dielectrics exhibit large ca-
pacitanceand ESRvariation with temperature. When
using this capacitor, a minimum 10uF or more may
be required to ensure the stability at low temperature
operation. Use a bypass capacitor at BP pin for low
output nvise. Increasing the capacitance will slightly
decrease the output noise, but increase the start-up
time.
Reverse Current Protection
TheAPL5501/2/3 havean internal reverse protection,
it does not need an external schottky diode to con-
nect the regulator input and output. If the output volt-
age is forced above the input voltage by more than
11mV, the IC will be shutdown and the ground pin
current is below 0.1uA.
Shutdown/Enable
TheAPL5501/2/3haveanactive highenablefunction.
Force EN high (>1.6V) enables the regulator, EN low
(<0.4V) disablesthe regulator and enter the shutdown
mode. In shutdown mode, the quiescent current can
reduce below 1uA. The EN pin cannot be floating, a
floating EN pin may cause an indeterminate state on
the output. If it is no use, connect to VIN for normal
operation.
Load-Transient Considerations
The APL5501/2/3 load-transient response graphs in
typical characteristics show the transient response.
A step change in the load current from 0mA to 500mA
at 1us will cause a 100mV transient spike. Larger
output capacitor and lower ESR can reduce transient
spike.
Current Limit
The APL5501/2/3 have a current limit protection. The
ouptut voltage will drop close to zero volt, when load
current reaches the limit, and then the load current
will be limited at 150mA after output voltage is below
0.7V. When the load current back to the value where
limiting started, the output voltage and current will re-
turn to normal value. When output is shorted to
ground, the APL5501/2/3 will keep short circuit cur-
rent at 150mA .
Input-Output (Dropout)Voltage
Theminimum input-outputvoltagedifference(dropout)
determines the lowest usable supply voltage. In bat-
tery-powered systems, this will determine the useful
Copyright ã ANPEC Electronics Corp.
11
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Rev. B.2 - May., 2005
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