LINEAR TECHNOLOGY LTC4606 Technical data
L DESIGN FEATURES
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
by Judy Sun, Jian Yin, Sam Young and Henry Zhang
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 portion 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 transitions and high switching frequencies
Table 1. Feature comparison of ultralow noise µModule regulators
Feature LTM4606 LTM4612
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.
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 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
IN
V
IN
V
OUT
I
OUT
CISPR 22 Class B Compliant
Output Voltage Tracking and Margining
PLL Frequency Synchronization
±1.5% Total DC Error
Power Good Output
Current Foldback Protection
Parallel/Current Sharing
Low Input and Output Referred Noise
Ultrafast Transient Response
Current Mode Control
Programmable Soft-Start
Output Overvoltage Protection
Package 15mm × 15mm × 2.8mm 15mm × 15mm × 2.8mm
4.5V to 28V 5V to 36V
0.6V to 5V 3.3V to 15V
6A DC Typical, 8A Peak 5A DC Typical, 7A Peak
L L
L L
L L
L L
L L
L L
L L
L L
L L
L L
L L
L L
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Linear Technology Magazine • January 2009
DESIGN FEATURES L
+
INTERNAL
COMP
SGND
COMP
PGOOD
RUN
>1.9V = ON
<1V = OFF
MAX = 5V
MARG1
MARG0
MPGM
FCB
PLLIN
C
SS
INTV
CC
DRV
CC
TRACK/SS
V
FB
f
SET
50k
41.2k
R
FB
19.1k
50k
60.4k
V
OUT
5.1V
ZENER
POWER CONTROL
M1
V
IN
4.5V TO 28V
V
D
V
OUT
2.5V
AT 6A
M2
50k
22µF
1.5µF
C
IN
+
C
OUT
PGND
C
D
10k
4.7µF
INPUT
FILTER
NOISE
CANCEL-
LATION
LOAD CURRENT (A)
0
EFFICIENCY (%)
100
90
70
80
60
50
654321
1.2V
OUT
1.5V
OUT
2.5V
OUT
3.3V
OUT
5V
OUT
LOAD CURRENT (A)
0.0
EFFICIENCY (%)
75
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
65
90
70
95
60
55
85
80
24V
IN,
12V
OUT
DCM
CCM
P
GOOD
RUN
V
D
INTV
CC
DRV
CC
f
SET
TRACK/SS
COMP
FCB
MARG0
MARG1
MPGM
V
OUT
V
FB
V
IN
C4
0.01µF
C3
100pF
C
OUT1
22µF
25V
C
OUT2
180µF
16V
V
OUT
12V
4.5A
C1
10µF
50V
C
IN
10µF x 2
50V
V
IN
18V
TO 36V
PLLIN
CLOCK SYNC
ON/OFF
LTM4612
SGND PGND
MARGIN
CONTROL
R4
100k
R
SET
5.23k
R1
392k
5% MARGIN
Figure 1. Simplified block diagram of the LTM4606 (LTM4612 is similar). Only a few
capacitors and resistors are required to build a complete wide-input-range regulator.
lab testing. See Table 1 for a feature
comparison of these two parts.
Both µModule regulators are offered in space saving, low profile and
thermally enhanced 15mm × 15mm ×
2.8mm LGA packages, so they can be
placed on the otherwise unused space
at the bottom of PC boards for highaccuracy point-of-load regulation. This
is not possible with linear regulators
Figure 2. Efficiency of the
LTM4606 with a 12V input.
that require a bulky cooling system.
Almost all support components are
integrated into the µModule package,
so layout design is relatively simple,
Figure 3. A few capacitors and resistors complete an 18V–36V input, 12V/4.5A output design.
Linear Technology Magazine • January 2009
requiring only a few input and output
capacitors.
For more output power, both parts
can be easily paralleled, where output
currents are automatically shared
due to the current mode control
structure.
Easy Power Supply Design
with Ultralow Noise
µModule Regulators
With a few external input and output capacitors, the LTM4612 can
deliver 4.5A of DC output current
Figure 4. Efficiency for the circuit in Figure 3.
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