APL5915 Anpec Electronics Corporation, APL5915 Datasheet - Page 14

• Manufacturer Part Number: APL5915
• Description: 0.8v Reference Ultra Low Dropout 0.2v@1.5a Linear Regulator
• Manufacturer: Anpec Electronics Corporation

APL5915
Application Information (Cont.)
The APL5915 is designed with a programmable
feedback compensation adjusted by an external
feedback network for the use of wide ranges of ESR
and capacitance in all applications. Ultra-low-ESR
capacitors (such as ceramic chip capacitors) and low-
ESR bulk capacitors (such as solid Tantalum, POSCap,
and Aluminum electrolytic capacitors) can all be used
as an output capacitor. The value of the output
capacitors can be increased without limit.
During load transients, the output capacitors,
depending on the stepping amplitude and slew rate of
load current, are used to reduce the slew rate of the
current seen by the APL5915 and help the device to
minimize the variations of output voltage for good
transient response. For the applications with large
stepping load current, the low-ESR bulk capacitors
are normally recommended.
Decoupling ceramic capacitors must be placed at the
load and ground pins as close as possible and the
impedance of the layout must be minimized.
Input Capacitor
The APL5915 requires proper input capacitors to sup-
ply current surge during stepping load transients to
prevent the input rail from dropping. Because the
parasitic inductor from the voltage sources or other
bulk capacitors to the VIN pin limit the slew rate of the
surge currents, more parasitic inductance needs more
input capacitance.
Ultra-low-ESR capacitors (such as ceramic chip
capacitors) and low-ESR bulk capacitors (such as solid
tantalum, POSCap, and Aluminum electrolytic
capacitors) can all be used as an input capacitor of
VIN. For most of applications, the recommended input
capacitance of VIN is 10 F at least. If the drop of the
input voltage is not cared, the input capacitance can
be less than 10 F. More capacitance reduces the
variations of the input voltage of VIN pin.
Output Capacitor (Cont.)
Copyright
Rev. A.3 - Apr., 2008
ANPEC Electronics Corp.
14
Feedback Network
Figure 1 shows the feedback network among VOUT,
GND, and FB pins. It works with the internal error
amplifier to provide proper frequency response for the
linear regulator. The ESR is the equivalent series
resistance of the output capacitor. The C
capacitance in the output capacitor. The V
setting of the output voltage.
The feedback network selection depends on the values
of the ESR and C
three conditions:
V
APL5915
• Condition 1 : Large ESR ( 18m )
• Condition 2 : Middle ESR
ERR
- Select the R1 in the range of 400 ~ 2.4k
- Calculate the R2 as the following :
- Calculate the C1 as the following :
- Calculate the R1 as the following:
R1(k
R2(k
10
EAMP
V
R1(k
OUT
)
)
V
(V)
ESR(m
REF
R1(k
)
2157
C1(nF)
OUT
VOUT
FB
)
Figure 1
V
V
)
which has been classified into
FB
OUT
37.5
0.8(V)
(V)
R1
40
R2
-
V
V
R1(k
0.8(V)
OUT
OUT
(V)
(V)
www.anpec.com.tw
)
..........
C1
......
15
.........
(2)
OUT
(1)
OUT
ESR
is ideal
V
C
is the
OUT
OUT
(3)