APL5101/2
Application Information
Capacitor Selection and Regulation Stability
resulting in a pulsed output during continuous thermal
protection. Thermal protection is designed to protect
the IC in the event of fault conditions. For continual
operation, donot exceedtheabsolutemaximum junction
temperature rating of TJ = +140°C.
The APL5101/2 use at least a 1mF capacitor on the
input. This capacitor can use Aluminum, Tantalum or
Ceramic capacitors. Input capacitor with large value
and low ESR provides better PSRR and line transient
response.Theoutput capacitoralsocanuseAluminum, Operating Region and Power Dissipation
Tantalum or Ceramic capacitor, and its proper values
The thermal resistance of the case and circuit board,
is recommended 1mF, ESR must be above 10mW
ambient and junction air temperature, and the rate of
Large output capacitor values can reduce noise and
air flow all control the APL5101/2’s maximum power
improve load-transient response, stability, and PSRR.
dissipation. The power dissipation across the device
With X5R and Y5V dielectrics, 1mF is sufficient at all
is P = IOUT(VIN-VOUT). The maximum power dissipation
operatingtemperatures.Theselection of output capacitor
is:
isimportant because it with COUT form azero toprovide
PMAX = (TJ-TA) / (qJC +qCA )
the sufficient phase margin.
where TJ-TA isthe temperature difference between the
Input-Output (Dropout) Voltage
junction and ambient air. qJC is the thermal resistance
of the package, qCA is the thermal resistance through
the printed circuit board, copper traces, and other
materialsto thesurroundingair. TheGNDpin provides
an electrical connectionto groundand channelingheat
away. The printed circuit board (PCB) forms a heat
sink and dissipates most of the heat into ambient air.
Theminimuminput-outputvoltagedifferential(dropout)
determines the lowest usable supply voltage. The
dropout voltage is a function of drain-to-source on
resistance multiplied by the load current.
Current Limit and Short Circuit
APL5101/2 include a current-limit circuitry for this
linear regulator. The current limit protection, which
sense the current flows the P-channel MOSFET, and
controls the output voltage. The point where limiting
occurs is IOUT=300mA. When output is shorted to
ground, the APL5101/2 will keep short circuit current
at 50mA .This design is a method for an indefinite
amount of time without damaging to the part.
Thermal Protection
Thermal protection limitstotal power dissipation inthe
APL5101/2. When the junction temperature exceeds
TJ = +135°C, the thermal sensor generate alogic signal
to turn off the pass transistor and let IC to cool.When
the IC’s junction temperature cools by 20°C, the
thermal sensor will turn the pass transistor on again,
Copyright ã ANPEC Electronics Corp.
9
www.anpec.com.tw
Rev. A.1 - Jun., 2005
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
