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Linear Technology Magazine • January 2009
L DESIGN FEATURES
Introduction
Power supply designers face many
tradeoffs. Need high efficiency, large
conversion ratios, high power and
good thermal performance? Choose a
switching regulator. Need low noise?
Choose a linear regulator. Need it
all? Compromise. One compromise
is to follow a switcher with a linear
regulator (or regulators). Although this
cleans up the output noise relative to
a switcher-only solution, a good por-
tion of the conducted and radiated
EMI remains—even if ferrite beads,
π filters, and LC filters are used. The
problem can always be traced back to
the switcher, where fast dI/dt transi-
tions and high switching frequencies
Ultralow Noise 15mm ×15mm × 2.8mm
µModule Step-Down Regulators Meet
the Class B of CISPR 22 and Yield
High Efficiency at up to 36V
IN
by Judy Sun, Jian Yin, Sam Young and Henry Zhang
lead to high frequency EMI, but
some applications, especially those
with large conversion ratios, require
a switcher.
Fortunately, the LTM4606 and
LTM4612 µModule regulators offer the
advantages of a switching regulator
while maintaining ultralow conducted
and radiated noise. These µModule
step-down regulators are designed to
achieve both high power density and
meet EMC (electromagnetic compat-
ibility) standards. The integrated
ultralow noise feature allows both
devices to pass the Class B of CISPR
22 radiated emission limit, thus
eliminating expensive EMI design and
These µModule step-down
regulators are designed
to achieve both high
power density and meet
EMC (electromagnetic
compatibility) standards.
The integrated ultralow
noise feature allows both
devices to pass the Class
B of CISPR 22 radiated
emission limit, thus
eliminating expensive EMI
design and lab testing.
Table 1. Feature comparison of ultralow noise µModule regulators
Feature LTM4606 LTM4612
V
IN
4.5V to 28V 5V to 36V
V
OUT
0.6V to 5V 3.3V to 15V
I
OUT
6A DC Typical, 8A Peak 5A DC Typical, 7A Peak
CISPR 22 Class B Compliant
L L
Output Voltage Tracking and Margining
L L
PLL Frequency Synchronization
L L
±1.5% Total DC Error
L L
Power Good Output
L L
Current Foldback Protection
L L
Parallel/Current Sharing
L L
Low Input and Output Referred Noise
L L
Ultrafast Transient Response
L L
Current Mode Control
L L
Programmable Soft-Start
L L
Output Overvoltage Protection
L L
Package 15mm × 15mm × 2.8mm 15mm × 15mm × 2.8mm
