MP4558

– 1A, 2MHz, 55V STEP-DOWN CONVERTER

MP4558 Rev. 1.01

www.MonolithicPower.com

16

10/28/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2013 MPS. All Rights Reserved.

place the input decoupling capacitor and the

catch diode as close to the MP4558 (VIN pin, SW

pin and PGND) as close as possible with short

and wide traces. This can help to greatly reduce

the voltage spikes on the SW node, and lower

the EMI noise level.

Route the feedback trace as far from the inductor

and noisy power traces as possible. If possible,

run the feedback trace on the opposite side of

the PCB opposite from the inductor with a ground

plane

separating

the

two.

Placing

the

compensation components close to the MP4558.

Avoid placing the compensation components

close to or under the high-dv/dt SW node, or

inside the high-di/dt power loop. If this is not

possible, route a ground plane to isolate the

circuit. Switching loss is expected to increase at

high switching frequencies.

To help to improve the thermal conduction, add

grid of thermal vias under the exposed pad. use

small vias (15mil barrel diameter) so that the

plating process fills the holes, thus aiding

conduction to the other side. Excessively large

holes can cause solder wicking during the reflow

soldering process. The typical pitch (distance

between the centers) between thermal vias is

typically 40mil.

External Bootstrap Diode

An external bootstrap diode may enhance the

regulator efficiency. For the cases described

below, add an external BST diode from 5V to the

BST pin:



There is a 5V rail available in the system;





This diode is also recommended for high-duty

–

cycle

operation

(when

>

65%)

applications.

The bootstrap diode can be a low-cost one such

as IN4148 or BAT54.

Figure 2: External Bootstrap Diode

At no load or light load, the converter may

operate in pulse-skipping mode to maintain the

output voltage in regulation: there is less time to

refresh the BS voltage. For sufficient gate voltage

to be greater than 3.3V+3V=6.3V for sufficient

BST voltage at no load or light load. To meet this

requirement, the EN pin can program the input