APL5912KAC-TRG Ver la hoja de datos (PDF) - Anpec Electronics
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APL5912KAC-TRG Datasheet PDF : 20 Pages
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APL5912
Application Information
Power Sequencing
The power sequencing of VIN and VCNTL is not neces-
sary to be concerned. However, do not apply a voltage to
VOUT for a long time when the main voltage applied at
VIN is not present. The reason is the internal parasitic
diode from VOUT to VIN conducts and dissipates power
without protections due to the forward-voltage
Output Capacitor
The APL5912 requires a proper output capacitor to main-
tain stability and improve transient response over tem-
perature and current. The output capacitor selection is to
select proper ESR (equivalent series resistance) and
capacitance of the output capacitor for good stability and
load transient response.
The APL5912 is designed with a programmable feed-
back compensation adjusted by an external feedback net-
work for the use of wide ranges of ESR and capacitance in
all applications. Ultra-low-ESR capacitors (such as ce-
ramic 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 APL5912 and help the device to minimize the varia-
tions 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 imped-
ance of the layout must be minimized.
Input Capacitor
The APL5912 requires proper input capacitors to supply
current surge during stepping load transients to prevent
the input rail from dropping. Because the parasitic induc-
tor 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
applications, the recommended input capacitance of VIN
is 10µF at least. If the drop of the input voltage is not
cared, the input capacitance can be less than 10µF. More
capacitance reduces the variations of the input voltage of
VIN pin.
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 COUT is ideal capacitance in the output
capacitor. The VOUT is the setting of the output voltage.
APL5912
V ERR
EAMP
VR E F
VOUT
R1
FB
VFB
R2
VOUT
ESR
C1
C OUT
Figure 1
The feedback network selection, depending on the val-
ues of the ESR and COUT, has been classified into three
conditions :
•Condition 1 : Large ESR ( ≥18mΩ)
- Select the R1 in the range of 400Ω ~ 2.4kΩ
- Calculate the R2 as the following:
R2(kΩ) = R1(kΩ) ⋅
0.8(V)
.......... (1)
VOUT(V) - 0.8(V)
- Calculate the C1 as the following:
10 ⋅ VOUT(V) ≤ C1(nF) ≤ 40 ⋅ VOUT(V) ...... (2)
R1(kΩ)
R1(kΩ)
•Condition 2 : Middle ESR
- Calculate the R1 as the following:
R1(kΩ) = 1500 − 37.5 ⋅ VOUT(V) + 30 ......... (3)
ESR(mΩ)
Copyright © ANPEC Electronics Corp.
13
Rev. A.10 - Oct., 2009
www.anpec.com.tw
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