Datasheet

ADP1864-EVALZ
Rev. A | Page 8 of 12
WEB TOOL INTERFACE
05612-019
Figure 18. Web Tool Interface
ENTER PERFORMANCE SPECIFICATIONS
In this section, the user can provide the specifications on how
the power supply being designed needs to perform. The voltage
range for the first two pull-down menus (Vinmin and Vinmax)
is 3.15 V − 14 V. In the third pull-down menu, the user provides
the required regulated output voltage (Vout), which needs to be
less than Vinmin and Vinmax, because this tool is to be used
with the buck topology. The next pull-down menu is the
required output current (Ioutmax). It is wise to design for the
peak current the regulator needs to provide, even if the peak is
required for only a short period of time. Without taking this
into consideration, it is possible to hit current limit when peak
current is needed. The information provided in the ambient
temperature (Tmax ambient) pull-down menu allows the
estimated temperature to be computed for each component.
This is a required piece of information to ensure that the parts
selected are thermally capable of handling the rise in
temperature associated with internal losses of the parts. The
switching frequency is internally set in the
ADP1864 to
580 kHz. There is a tolerance on this specification, and the
minimum and maximum limits can be selected through the
pull-down menu (Fsw). When the switching frequency is at a
minimum, the current in the inductor rises to a slightly higher
amplitude than in the nominal switching frequency case.
Consequently, the voltage across the sense resistor will also be
higher, which needs to be accounted for when the tool calcu-
lates the current limit trip point. A robust design should always
consider this minimum switching frequency. Additionally, the
performance of the system can be viewed when selecting the
maximum switching frequency from the pull-down menu.
The inductor ripple selection (IripplemaxL) affects several
parameters. As a general guideline, it is recommended to set
this value between 30% to 50% of the output load. A small
inductor allows energy to be transferred from the input to the
output more quickly during a load step, resulting in a smaller
output voltage excursion during the load step. On the other
hand, a small inductor requires a higher current rating of the
inductor itself. In other words, the ripple current is inversely
proportional to the size of the inductor. Higher ripple current
also translates to higher output voltage ripple for a fixed
capacitance value. Selecting the maximum output voltage ripple
(Vripple ppk) allowed from the pull-down menu determines the
amount and type (MLCC, aluminum electrolytic, etc.) of output
capacitance needed and correspondingly how the compensation