LM2621

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SNVS033D – MAY 2004 – REVISED NOVEMBER 2015

9 Power Supply Recommendations

The power line feeding the LM2621 should have low impedance. The input capacitor of the system should be

placed as close to VIN as possible. If the power supply is very noisy, an additional bulk capacitor might be

necessary in the system to ensure that clean power is delivered to the IC.

10 Layout

10.1 Layout Guidelines

High switching frequencies and high peak currents make a proper layout of the PC board an important part of

design. Poor design can cause excessive EMI and ground-bounce, both of which can cause malfunction and loss

of regulation by corrupting voltage feedback signal and injecting noise into the control section.

Power components - such as the inductor, input and output filter capacitors, and output diode - should be placed

as close to the regulator IC as possible, and their traces should be kept short, direct and wide. The ground pins

of the input and output filter capacitors and the PGND and SGND pins of LM2621 should be connected using

short, direct and wide traces. The voltage feedback network (RF1, RF2, and CF1) should be kept very close to the

FB pin. Noisy traces, such as from the SW pin, should be kept away from the FB and VDD pins. The traces that

run between Vout and the FB pin of the IC should be kept away from the inductor flux. Always provide sufficient

copper area to dissipate the heat due to power loss in the circuitry and prevent the thermal protection circuitry in

the IC from shutting the IC down.

10.2 Layout Example

Figure 19. LM2621 PCB Layout

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