BL8022
switching currents do not pass through the input
source. The output capacitor keeps output ripple
small and ensures control-loop stability. The output
capacitor must also have low impedance at the
switching frequency. Ceramic, polymer, and
tantalum capacitors are suitable, with ceramic
exhibiting the lowest ESR and high-frequency
impedance. Output ripple with a ceramic output
capacitor is approximately as follows:
VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT)]
If the capacitor has significant ESR, the output
ripple component due to capacitor ESR is as follows:
VRIPPLE(ESR) = IL(PEAK) x ESR
particular attention. Follow these guidelines for
good PC board layout:
1) Place decoupling capacitors as close to the IC as
possible
2) Connect input and output capacitors to the
same power ground node with a star ground
configuration then to IC ground.
3) Keep the high-current paths as short and wide
as possible. Keep the path of switching current
(C1 to IN and C1 to GND) short. Avoid vias in
the switching paths.
4) If possible, connect IN, SW, and GND separately
to a large copper area to help cool the IC to
further improve efficiency and long-term
reliability.
5) Ensure all feedback connections are short and
direct. Place the feedback resistors as close to
the IC as possible.
6) Route high-speed switching nodes away from
sensitive analog areas
Application Information
Layout is critical to achieve clean and stable
operation. The switching power stage requires
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