ACT5880
Rev 2, 03-Sep-13
this change asserts interrupt to alert the system for
out of regulation.
Component Selection
Each step-down DC/DC regulator utilizes current-
mode control and
a
proprietary internal
compensation scheme to simultaneously simplify
external component selection and optimize
transient performance over its full operating range.
No compensation design is required; simply follow a
few simple guidelines described below when
choosing external components.
Inductor Selection
The inductors with inductance 1.5µH to 2.2µH for
REG1 and 1.5µH to 3.3µH for REG2 are
recommended.
Input and Output Capacitor Selection
REG1 and REG2 are designed to operate with
small 22µF~27µF and 10µF~22µF output
capacitors respectively, over their output voltage
ranges. The input bypass capacitors sink the quick
component in current, help in suppressing of EMI
and improving the efficiency. Capacitance in range
2μF to 10μF is commonly sufficient. X5R and X7R
dielectrics are recommended for those capacitors
for their suitable and stable characteristics to better
performance.
PCB Layout Considerations
The high frequency element in the inductor current
alternates between the switch ground path and the
input bypass capacitor ground path. Place and
route the two paths close, then place the ground
end of output capacitor close to them, then place
the inductor close is the better order in layout
design. Though the practice is difficult to place all
components close to the ACT5880, it is necessary
to give the step-down DC/DCs the priority for closer
placement.
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