Copyright ANPEC Electronics Corp.
Rev. B.3 - Sep., 2008
APL5901/2
www.anpec.com.tw10
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 APL5901/2 use a p-chan-
nel MOSFET pass transistor, the dropout voltage is the
function of drain-to-source on-resistance (RDS(ON)) multi-
plied by the load current.
The APL5901/2 load-transient response graphs in typical
characteristics show the transient response. A step change
in the load current from 10mA to 900mA at 10µs will cause
a 20mV transient spike. Larger output capacitor and lower
ESR can reduce transient spike.
Application Information
The APL5901/2 use at least a 1µF capacitor on the input,
and this capacitor can be Aluminum, Tantalum, or Ce-
ramic capacitor. The input capacitor with larger value and
lower ESR provides better PSRR and line-transient
response.
Load-Transient Consideration
Input-Output (Dropout)Voltage
Reverse Current Protection
Current Limit
The APL5901/2 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 200mA after output voltage is below 0.7V. When the
load current back to the value where limiting started, the
output voltage and current will return to normal value.
When output is shortened to the ground, the APL5901/2
will keep short circuit current at 200mA .
Shutdown/Enable
The APL5901/2 have an active high enable function. Force
EN high (>1.6V) enables the regulator, EN low (<0.4V)
disables the regulator and enter the shutdown mode. In
Capacitor Selection and Regulator Stability
The output capacitor also can use Aluminum, Tantalum,
or Ceramic capacitor, and a minimum value of 4.7µF and
ESR above 0.02Ω is recommended. A larger output ca-
pacitor can reduce 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
10µF or more may be required to ensure that 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.
The APL5901/2 have an internal reverse protection, it does
not need an external schottky diode to connect the regu-
lator input and output. If the output voltage is forced above
the input voltage by more than 11mV, the IC will be shut-
down and the ground pin current is below 0.1µA.
Thermal Protection
Thermal protection limits total power dissipation in the
device. When the junction temperature exceeds TJ=+15oC,
the thermal sensor generates a logic signal to turn off the
pass transistor and allows IC to cool. When the IC’s junc-
tion temperature is down by 10oC, the thermal sensor
will turn the pass transistor on again, resulting in a pulsed
output during continuous thermal protection. Thermal
protection is designed to protect the APL5901/2 in the
event of fault conditions. For continuous operation, do
not exceed the absolute maximum junction temperature
of TJ=+150oC.
Operating Region and Power Dissipation
The thermal resistance of the case to circuit board, and
the rate of air flow all control the APL5901/2’s maximum
power dissipation. The power dissipation across the
device is PD = IOUT (VIN-VOUT) and the maximum power dis-
sipation is:
PDMAX = (TJ-TA) / (θJC +θCA)
shutdown mode, the quiescent current can reduce below
1µA. 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.
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 APL5901 provides an electrical con-
nection to the ground and channeling heat away. If power
dissipation is large, connect the GND pin to the ground
using a large pad or a ground plane can improve the
problem of over heat of IC.