AME, Inc.
AME5138
CAPACITOR SELECTION
Choose low ESR capacitors for the output to minimize
output voltage ripple. Multilayer ceramic capacitors are the
best choice. For most applications, a 1µF ceramic capaci-
tor is sufficient. For some applications a reduction in output
voltage ripple can be achieved by increasing the output ca-
pacitor. Local bypassing for the input is needed on the
AME5138. Multilayer ceramic capacitors are a good choice
for this as well. A 4.7µF capacitor is sufficient for most appli-
cations. For additional bypassing, a 100nF ceramic capaci-
tor can be used to shunt high frequency ripple on the input.
Micropower Step-Up
DC/DC Converter
LAYOUT CONSIDERATIONS
The input bypass capacitor C
IN
, as shown in Figure 3,
must be placed close to the IC. This will reduce copper
trace resistance which effects input voltage ripple of the IC.
For additional input voltage filtering, a 100nF bypass ca-
pacitor can be placed in parallel with C
IN
to shunt any high
frequency noise to ground. The output capacitor, C
OUT
, should
also be placed close to the IC. Any copper trace connec-
tions for the C
OUT
capacitor can increase the series resis-
tance, which directly effects output voltage ripple. The feed-
back network, resistors R1 and R2, should be kept close to
the FB pin to minimize copper trace connections that can
inject noise into the system. The ground connection for the
feedback resistor network should connect directly to an
analog ground plane. The analog ground plane should tie
directly to the GND pin. If no analog ground plane is avail-
able, the ground connection for the feedback network should
tie directly to the GND pin. Trace connections made to the
inductor and schottky diode should be minimized to reduce
power dissipation and increase overall efficiency.
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AME [ ANALOG MICROELECTRONICS ]
