Copyright ANPEC Electronics Corp.
Rev. C.6 - Mar., 2008
APL1117
www.anpec.com.tw10
Input Capacitor
An input capacitor of 10µF or greater is recommended.
Tantalum, or aluminum electrolytic capacitors can be
used for bypassing. Larger Values will improve ripple
rejection by bypassing the input to the regulator.
Output Capacitor
The APL1117 requires an output capacitor to maintain
stability and improve transient response. Proper
capacitor selection is important to ensure proper
operation. The APL1117 output capacitor selection is
dependent upon the ESR (equivalent series resistance)
of the output capacitor to maintain stability. When the
output capacitor is 10uF or greater, the output capacitor
should have an ESR less than 1Ω.This will improve
transient response as well as promote stability. A
low-ESR solid tantalum capacitor works extremely well
and provides good transient response and stability over
temperature.
Aluminum electrolytics can also be used, as long as
the ESR of the capacitor is <1Ω. The value of the output
capacitor can be increased without limit. Higher
capacitance values help to improve transient response
and ripple rejection and reduce output noise.
Figure 2. Connections for Best Load Regulation
Application Information (Cont.)
Load Regulation (Cont.)
VIN
APL1117
OUTIN ADJ
R1
R2
Rp
PARASITIC
LINE RESISTANCE
CONNECT
R1 TO CASE
CONNECT
R2 TO LOAD
RL
Ripple Rejection
The curves for Ripple Rejection were generated using
an adjustable device with the adjust pin bypassed. With
a 22µF bypassing capacitor 75dB ripple rejection is
obtainable at any output level. The impedance of the
adjust pin capacitor, at the ripple frequency, should
be < R1. R1 is normally in the range of 100Ω-200Ω.
The size of the required adjust pin capacitor is a
function of the input ripple frequency. At 120Hz, with
R1=100Ω, the adjust pin capacitor should be 13µF.
For fixed voltage devices, and adjustable devices
without an adjust pin capacitor, the output ripple will
increase as the ratio of the output voltage to the
reference voltage (VOUT /VREF ).
Thermal Considerations
The APL1117 regulators have thermal protection to limit
junction temperature to 150ºC. However, device
functionality is only guaranteed to a maximum junction
temperature of +125ºC.
A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature
of the application. Figure 3&4 show for the TO-252
and SOT-223 the measured values θ(J-A) for different
copper area sizes using a 2 layers, 1.6mm, and 6Sq.
cm FR-4 PCB with 2oz. copper and a ground plane
layer on the backside area used for heatsinking. It
can be used as a rough guideline in estimating thermal
resistance. Both the TO-252 and SOT-223 packages
use a copper plane on the PCB and the PCB itself as
a heatsink. To optimize the heat sinking ability of the
plane and PCB, solder the tab of the package to the
plane.