Copyright ANPEC Electronics Corp.
Rev. B.8 - Jul., 2009
APL5151/2/3/4
www.anpec.com.tw9
Application Information
Capacitor Selection and Regulator Stability
The APL5151/2/3/4 use at least a 1µF 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 minimum value of
1µF and ESR above 0.06Ω is recommended. The curve
of the stable region in typical characteristics shows the
appropriate output capacitor ESR for different load cur-
rent stable operation. A larger output capacitor can re-
duce noise and improve load-transient response, stability,
and PSRR. Note that some ceramic dielectrics exhibit
large capacitance and ESR variation with temperature.
When using this capacitor, a minimum 2.2µF or more
may be required to ensure the stability at low tempera-
ture operation. Use a bypass capacitor at BP pin for low
output noise. Increasing the capacitance will slightly de-
crease the output noise but increase the start-up time
(See Shutdown Exit Delay and Output Noise vs. Bypass
Capacitor graph in the Typical Operating Characteristics).
Load-Transient Consideration
The APL5151/5152515/5153/5154 load-transient re-
sponse graphs in Typical Operating Characteristics show
the transient response. A step changes in the load cur-
rent from 1mA to 50mA at 1µs will cause a 60mV tran-
sient spike. Larger output capacitor and lower ESR can
reduce transient spike.
Input-Output (Dropout) Voltage
The minimum input-output voltage difference (dropout)
determines the lowest usable supply voltage. In battery-
powered systems, this will determine the useful end-of-
life battery voltage. Because the APL5151/5152/5153/
5154 use a p-channel MOSFET pass transistor, the drop-
out voltage is the function of drain-to-source on-resis-
tance (RDS(ON)) multiplied by the load current.
Reverse Current Protection
The APL5151/5152/5153/5154 have an internal reverse
protection, therefore, it is not necessary to use an exter-
nal Schottky diode to connect the regulator input and
output. If the output voltage is forced above the input volt-
Current Limit
The APL5151/5152/5153/5154 provide a current-limit
circuitry, which monitors and controls P-MOS’s gate
voltage, limiting the output current to 300mA. For reliable
operation, the device should not be operated in current
limit for extended period. When output is shortened to the
ground, the APL5151/5152/5153/5154 will keep short cir-
cuit current at 50mA
Thermal Protection
Thermal protection limits total power dissipation in the
device. When the junction temperature exceeds
TJ=+150°C, the thermal sensor generates a logic signal
to turn off the pass transistor and allows IC to cool. When
the IC’s junction temperature is down by 10°C, the ther-
mal sensor will turn the pass transistor on again, result-
ing in a pulsed output during continuous thermal
protection. Thermal protection is designed to protect the
APL5151/5152/5153/5154 in the event of fault conditions.
For continuous operation, the junction temperature can-
not exceed TJ=+125°C.
Operating Region and Power Dissipation
The thermal resistance of the case to circuit board, and
the rate of air flow all control the APL5151/5152/5153/
5154’s maximum power dissipation. The power dissi-
pation across the device is PD = IOUT (VIN-VOUT) and the
maximum power dissipation is:
PDMAX = (TJ-TA) / (θJC +θCA)
where TJ-TA is the temperature difference between the
junction and ambient air, θJC is the thermal resistance of
the package, and θCA is the thermal resistance through
the printed circuit board, copper traces, and other materi-
als to the ambient air.
The GND pin of the APL5151/5152/5153/5154 provide an
electrical connection to the ground and channeling heat
away. If power dissipation is large, connect the GND pin
to the ground using a large pad or ground plane, can
improve the problem of over heat of IC.
age by more than 11mV, the IC will be shutdown and the
ground pin current is below 0.1µA.