APL5910_09 Datasheet, PDF (11/17 Pages) Anpec Electronics Coropration – 1A, Ultra Low Dropout (0.12V Typical) Linear Regulator

APL5910
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 does 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 APL5910 requires a proper output capacitor to main-
tain stability and improve transient response. The output
capacitor selection is dependent upon ESR (equivalent
series resistance) and capacitance of the output capacitor
over the operating temperature.
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 output capacitors.
During load transients, the output capacitors which is de-
pending on the stepping amplitude and slew rate of load
current, are used to reduce the slew rate of the current
seen by the APL5910 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 imped-
ance of the layout must be minimized.
More capacitance reduces the variations of the supply
voltage on VIN pin.
Setting The Output Voltage
The output voltage is programmed by the resistor divider
connected to FB pin. The preset output voltage is calcu-
lated by the following equation :
VOUT
=
0.8
⋅
^{1 +}
R1
R2

........... (V)
where R1 is the resistor connected from VOUT to FB with
Kelvin sensing connection and R2 is the resistor con-
nected from FB to GND. A bypass capacitor (C1) may be
connected with R1 in parallel to improve load transient
response and stability.
Input Capacitor
The APL5910 requires proper input capacitors to supply
current surge during stepping load transients to prevent
the input voltage rail from dropping. Because the para-
sitic inductor from the voltage sources or other bulk ca-
pacitors to the VIN pin limits 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. However, if the drop of the input voltage
is not cared, the input capacitance can be less than 10µF.
Copyright © ANPEC Electronics Corp.
11
Rev. A.3 - Jun., 2009
www.anpec.com.tw