10

The high-side switch is then held off for a period sufficient

to allow inductor current to decay. When the output

voltage is close to the nominal regulation point, this will

look similar to constant current limiting. As the output

voltage falls, imposed off-time is such that the frequency

will drop so that the inductor will have appropriate time

to reset. This may cause the average current to reduce,

giving a mild ‘fold-back’ characteristic to the current limit,

where the average load current drops as the output

voltage collapses (although the peak current maintains its

nominal value). In a short-circuit condition, the system

runs continuously at this reduced frequency.

Load Transient Response

load transients. This is due to the nature of the proprietary

control method and the high di/dt allowed by the use of a

small inductor. This allows for best performance while

providing the benefit of using a small low cost output

output capacitor. (See the typical performance curves on

page 7).

X-EMI™ Inductor Technology

designers to draw their own inductors directly on the PC

board. This patented technology is called as X-EMI™

inductor technology and is different from conventional

PCB trace inductors. Conventional PCB trace inductors can

be used with high-frequency switchers, but they exhibit

significant EMI issues. X-EMI™ inductor technology solves

these EMI problems and can meet or exceed the EMI per-

formance of conventional chip inductors.

inductors adjacent to one another in anti-phase position,

where the magnetic fields of each inductor partially cancel

one another to reduce EMI. The net flux from the two

inductors, partially cancels the wide leakage paths caused

by the wide geometry, while still storing the energy of the

inductors in series. This approach uses multiple air core

inductors implemented using printed circuit traces.

Because these traces may be located on internal layers of

the PCB, inductors can be designed with almost no impact

on the available PCB area for components on the surface

of the board. (See the efficiency curves using X-EMI™

inductor technology on page 6).

External Components

The input and output capacitors used for the operation of

operate with the input and output capacitance of 1μF

typical. In practice, the self-resonant frequency of surface

mount capacitors of this type is well below 20MHz ripple

frequency, so efforts to minimize output ripple may best

be focused on minimizing the inductance of the output

capacitor and the length of the circuit path to ground

rather than on increasing the capacitance value of the

output capacitor.

The inductor should be a high current inductor rated for

currents at least up to 1A. Typical power inductors may be

too lossy at 20MHz unless specifically designed for high

frequency operation. For inductor value of 220nH, it may

be preferred to use wire-wound RF chokes, many of which

are rated for appropriate currents.

Some Recommended External Components

Value

Manufacturer

Part Number

Package

L

0.22μH

Coilcraft

XFL2005-221ME

2x2mm

0.24μH

Coilcraft

0603LS-241XJL

0603

0.22μH

Wurth

Elektronik

74479762122

0603

CIN

1μF

Murata

GRM155R61C105KA12

0402

COUT

1μF

Murata

GRM155R61C105KA12

0402

Applications Information (Cont.)

Figure 1. Top view of an evaluation board with X-EMI inductor