BL8021 datasheet(6/7 Pages) BELLING

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BL8021

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

Application Information

Layout is critical to achieve clean and stable

operation. The switching power stage requires

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.

Route high-speed switching nodes away from

sensitive analog areas

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