SC220EVB Semtech, SC220EVB Datasheet - Page 10

• Manufacturer Part Number: SC220EVB
• Description: SC220 20 MHz Step-Down Regulator (SOIC-8) Evaluation Board
• Manufacturer: Semtech

Applications Information (Cont.)
dition. When the current fl owing through the high-side
PMOS switch exceeds the current limit, the PMOS switch
is turned off . The high-side switch is then held off for a
period suffi cient 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, the imposed off -time is such that
the frequency will drop, thus the inductor will have appro-
priate 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
The SC220 features excellent regulation during line and
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
capacitor.
voltage
1mA to 650mA within hundreds of nanoseconds, using
typical a 1μF output capacitor. (See the typical perfor-
mance curves on page 7).
X-EMI™ Inductor Technology
The SC220 is the industry’s fi rst buck regulator that enables
designers to draw their own inductors directly on the PC
board. This patented technology is called X-EMI™ inductor
technology and is diff erent from conventional PCB trace
inductors. Conventional PCB trace inductors can be used
with high-frequency switchers, but they exhibit signifi cant
EMI issues. X-EMI™ inductor technology solves these EMI
problems and can meet or exceed the EMI performance of
conventional chip inductors.
X-EMI
inductors adjacent to each other in anti-phase position,
where the magnetic fi elds of each air-core inductor par-
tially cancel one another to reduce EMI. The net fl ux from
the two inductors, partially cancels the wide leakage paths
caused by the wide geometry, but is still able to store the
TM
during a load current step change from less than
technology works by placing two small air-core
V
OUT
shows only tens of millivolts of ripple
energy of the inductors in series. This approach uses mul-
tiple 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 effi ciency curves using
X-EMI™ inductor technology on page 6).
External Components
The input and output capacitors used for the operation of
the SC220 should be multilayer ceramic capacitors, prefer-
ably with X7R or X5R dielectric. The SC220 is optimized to
operate with typical 1μF input and output capacitance. In
practice, the self-resonant frequency of surface mount
capacitors of this type is well below the 20MHz ripple fre-
quency, so eff orts 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 specifi cally 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
C
C
L
OUT
IN
Figure 1. Top view of an evaluation board with X-EMI inductor
0.22μH
0.24μH
Value
1μF
1μF
Manufacturer
Coilcraft
Coilcraft
Murata
Murata
GRM155R61C105KA12
GRM155R61C105KA12
XFL2005-221ME
0603LS-241XJL
Part Number
SC220
Package
2x2mm
0603
0402
0402
10