APL5913 Anpec Electronics, APL5913 Datasheet - Page 13

• Manufacturer Part Number: APL5913
• Description: 0.8V Reference Ultra Low Dropout Linear Regulator
• Manufacturer: Anpec Electronics

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Application Information (Cont.)
APL5913
Output Capacitor (Cont.)
The APL5913 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), low-ESR
bulk capacitors (such as solid Tantalum, POSCap, and
Aluminum electrolytic capacitors) all can 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 APL5913 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 APL5913 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, are very good for the input capacitors An
aluminum electrolytic capacitor (>100mF, ESR
<300mW) is recommended as the input capacitor. It
is not necessary to use low-ESR capacitors. More
capacitance reduce the variations of the input voltage
of VIN pin.
Copyright
Rev. A.4 - May., 2005
ANPEC Electronics Corp.
13
Feedback Network
Figure 1 shows the feedback network between 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:
• Condition 1 : Large ESR ( 18m )
• Condition 2 : Middle ESR
V
APL5913
- 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:
10
R1
R2
ERR
(k
(k
V
R1
EAMP
)
)
OUT(V)
(k
R1
ESR
2157
)
V
(k
REF
C1
(m
)
V
)
(nF)
OUT
OUT(V)
VOUT
FB
37.5
Figure 1
, which has been classified into
0.8
V
40
FB
(V)
-
0.8
V
R1
V
R1
R2
OUT(V)
(V)
OUT(V)
(k
..........
)
15
......
www.anpec.com.tw
.........
(1)
C1
(2)
OUT
OUT
(3)
is ideal
ESR
is the
V
C
OUT
OUT