APL1581-15KA Anpec Electronics Corporation, APL1581-15KA Datasheet - Page 10

• Manufacturer Part Number: APL1581-15KA
• Description: Dual Input Low Dropout Regulator
• Manufacturer: Anpec Electronics Corporation

V
APL1581
Application Information (Cont.)
Grounding and Output Sensing (Cont.)
Stability and Output Capacitors
The circuit design of using the APL1581 series requires
an output capacitor as part of the device frequency
compensation. The following chart shows a stable re-
gion to select output capacitor for APL1581. This region
above the curve indicates minimum required ESR and
capacitance to maintain stability. However, the output ca-
pacitor should have an ESR less than 1 .
A low-ESR solid tantalum and aluminum electrolytic ca-
pacitor (ESR<1 ) works extremely well and provides good
transient response and stability over temperature. Ultra-
low-ESR capacitors, such as ceramic chip capacitors, may
promote unstable or under-damped transient response,
but proper ceramic chip capacitors placed near loads can
be used as decoupling capacitors.
Copyright
Rev. B.6 - Feb., 2009
CNTL
V
IN
100
80
60
40
20
0
1
Figure 2. Remote Voltage Sensing
ANPEC Electronics Corp.
VIN
VCNTL
Fixed Voltage
APL1581
Device
GND
VSENSE
10
VOUT
Capacitance( F)
Stable Region
100
RP
V
OUT
Load
1000
10
The output capacitors are also used to reduce the slew
rate of load current and help the APL1581 to minimize
variations of the output voltage, improving transient
response. For this purpose, the low-ESR capacitors are
recommended.
Input Capacitors
The input capacitors of VCNTL and VIN pins are not re-
quired for stability but for supplying surge currents during
large load transients, and this will prevent the input rail
from drooping and improve the performance of the
APL1581. Because parasitic inductors from voltage
sources or other bulk capacitors to the VCNTL and VIN
pins will limit the slew rate of the surge currents during
large load transients, resulting in voltage drop at VIN and
VCNTL pins.
A capacitor of 1 F (ceramic chip capacitor) or greater
(aluminum electrolytic capacitor) is recommended and
connected near VCNTL pin. For VIN pin, an aluminum
electrolytic capacitor (>33 F) is recommended. It is not
necessary to use low-ESR capacitors. More capacitance
reduces the variations of the input voltage at VIN pin.
Layout and Thermal Consideration
The APL1581 series have internal power and thermal
limiting (T
the device under overload conditions. However, maximum
junction temperature ratings should not be exceeded
under continuous normal load conditions. Careful con-
sideration must be given to all sources of thermal resis-
tance from junction to ambient, including junction-to-case,
case-to-heat sink interface, and heat sink resistance itself.
See Figure 3 The SOP-8P is a cost-effective package
featuring a small size as a standard SOP-8 and a bottom
thermal pad to minimize the thermal resistance of the
package, being applicable to high current applications.
The thermal pad is soldered to the top VOUT plane which
may be connected to internal or bottom VOUT plane by
vias to reduce the heat sink thermal resistance. Therefore,
the printed circuit board (PCB) forms a heat sink and
dissipates heat into ambient air.
J
=150
o
C typical) circuitry designed to protect
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