MP4460 – 2.5A, 4MHz, 36V STEP-DOWN CONVERTER

MP4460 Rev. 1.02

www.MonolithicPower.com

14

12/24/2013

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High Frequency Operation

The switching frequency of MP4460 can be

programmed up to 4MHz by an external resistor.

Please pay attention to the following if the

switching frequency is above 2MHz.

The minimum on time of MP4460 is about 80ns

(typ). Pulse skipping operation can be seen

more easily at higher switching frequency due

to the minimum on time. Recommended

operating voltage is 12V or below, and 24V or

below at 2MHz. Refer to Figure 2 below for

detailed information.

vs Switching Frequency

30

25

20

15

10

5

1500 2000 2500 3000 3500 4000

Since the internal bootstrap circuitry has higher

impedance, which may not be adequate to

charge the bootstrap capacitor during each

(1-D)×Ts charging period, an external bootstrap

charging diode is strongly recommended if the

switching frequency is above 2MHz (see

External Bootstrap Diode section for detailed

implementation information).

With higher switching frequencies, the inductive

so that the ESL of input/output capacitor

determines the input/output ripple voltage at

higher switching frequency. As a result of that,

high frequency ceramic capacitor is strongly

recommended as input decoupling capacitor

and output filtering capacitor for such high

frequency operation.

Layout becomes more important when the

device switches at higher frequency. It is

essential

to

place

the

input

decoupling

capacitor, catch diode and the MP4460 (Vin pin,

SW pin and PGND) as close as possible, with

traces that are very short and fairly wide. This

can help to greatly reduce the voltage spike on

SW node, and lower the EMI noise level as well.

Try to run the feedback trace as far from the

inductor and noisy power traces as possible. It

is often a good idea to run the feedback trace

on the side of the PCB opposite of the inductor

with a ground plane separating the two. The

compensation components should be placed

closed to the MP4460. Do not place the

compensation components close to or under

high dv/dt SW node, or inside the high di/dt

power loop. If you have to do so, the proper

ground plane must be in place to isolate those.

Switching loss is expected to be increased at

high switching frequency. To help to improve

the thermal conduction, a grid of thermal vias

can be created right under the exposed pad. It

is

recommended

that

they

be

small

(15mil barrel diameter) so that the hole is

essentially filled up during the plating process,

thus aiding conduction to the other side. Too

large a hole can cause ‘solder wicking’

problems during the reflow soldering process.

The pitch (distance between the centers) of

several such thermal vias in an area is typically

40mil. Please refer to the layout example on

EV4460 datasheet.