LINEAR TECHNOLOGY LTM4604-08 Technical data
L DESIGN FEATURES
V
IN
SV
IN
SW
RUN
PLLLPF
TRACK
V
OUT
FB
I
TH
I
THM
PGOOD
MGN
CLKOUT GND
CLKIN
4.87k
100μF
10μF
V
OUT
1.8V
8A
V
IN
3V TO 5.5V
LTM4608
SGND
V
IN
V
IN
V
IN
3.3V
PGOOD
COMP
LTM4604
RUN/SS
2.37k
22MF
6.3V
r2
V
OUT
2.5V
4A
10MF
6.3V
V
OUT
FB
TRACK
GND
LOAD CURRENT (A)
0
70
EFFICIENCY (%)
75
80
85
90
95
100
1.0 2.0 3.0 4.0
V
OUT
= 2.5V
VIN = 3.3V
Low Voltage, High Current Step-Down
µModule Regulators Put a (Nearly)
Complete Power Supply in a
15mm × 9mm × 2.8mm Package
by Judy Sun, Sam Young and Henry Zhang
Introduction
Endlessly increasing power density
requirements are a major driving force
behind the continuous need to find
new power supply solutions. Switching
regulators are the top choice for high
current applications because of their
high efficiency and high performance,
but high power density doesn’t come
for free with a switcher. Components
must be carefully chosen and laid
out to maximize efficiency, transient
response and thermal performance.
Making a high density switching power
supply requires significant design and
test time, or does it?
The LTM4604 and LTM4608 LTC
µModule switching regulators make
it possible to create high density
designs with minimal effort. Both
are high density power supplies for
≤5.5V input voltage, high output current, step-down applications. Each
µModule regulator comes in a 15mm
× 9mm LGA surface mount package
and is nearly self-contained—only a
few passive components are required
to complete a power supply design. The
switching controller, MOSFETs, inductor and all support components are
Figure 1. Only a few components are required
for a 2.5V/4A design with LTM4604.
already carefully chosen and laid out
in the package. Low profile packages
(2.3mm and 2.8mm, respectively) allow
them to be easily mounted in unused
space on the bottom of PC boards and
simplify thermal management.
The LTM4604 features a 2.375V
to 5.5V input range and a 0.8V to
5V output range, while the LTM4608
takes a 2.7V to 5.5V input to a 0.6V to
5V output. The LTM4604 can deliver
up to 4A continuous current with up
to 95% efficiency. The slightly higher
profile of the LTM4608 allows it to
deliver up to 8A continuous current
thanks to its high efficiency design and
low thermal impedance package.
Easy Design with
Few Components
Figure 1 shows a typical 2.5V/4A
design with LTM4604 and Figure 2
shows the resulting efficiency. Ceramic
input capacitors are integrated into
the µModule package—additional
input capacitors are only required if
a load step is expected up to the full
4A level. Additional required output
capacitance is typically in the range
of 22µF to 100µF. A single resistor on
the FB pin sets the output voltage.
For applications needing more
output current, the LTM4608 fits the
bill. Figure 3 shows a 1.8V/8A design
with LTM4608 and Figure 4 shows
its efficiency. As with the LTM4604,
the number of necessary external
components has been reduced to a
minimum, significantly simplifying
the design effort. Nevertheless, a very
fast transient response to the line and
load changes is guaranteed by the optimized design of the µModule’s high
switching frequency and current mode
control architecture. Furthermore, a
number of features can be enabled on
the LTM4604 and LTM460408 to suit
the needs of various applications.
Figure 2. High efficiency is achieved with the
LTM4604 in the application of Figure 1
28
Figure 3. Only a few components are required for a 1.8V/8A design with the LTM4608.
Linear Technology Magazine • September 2008
LOAD CURRENT (A)
0
70
EFFICIENCY (%)
75
80
85
90
95
100
2 4 6 8
10
V
OUT
= 1.8V
V
IN
= 5V
VIN = 3.3V
TOTAL LOAD CURRENT (A)
0 2 4 6 8 10 12 14 16 18
0
1
2
3
4
5
6
7
8
9
OUTPUT CURRENT OF EACH LTM4608 (A)
I
OUT1
I
OUT2
V
IN
SV
IN
SW
RUN
PLLLPF
TRACK
MODE
PHMODE
V
OUT
FB
I
TH
I
THM
PGOOD
BSEL
MGN
CLKOUT GND
CLKIN
100µF
6.3V
X5R
100pF
10µF
3.32k
V
OUT
1.5V
16A
V
IN
3V TO 5.5V
LTM4608
SGND
V
IN
SV
IN
SW
RUN
PLLLPF
TRACK
MODE
PHMODE
V
OUT
FB
I
TH
I
THM
PGOOD
BSEL
MGN
CLKOUT GND
CLKIN
10µF
100µF
6.3V
X5R
LTM4608
SGND
Figure 4. High efficiency is achieved with the
LTM4608 in the application of Figure 3.
Wealth of Features
Both LTM4604 and LTM4608 feature RUN pin control, output voltage
tracking selections and power good
indicators. For systems requiring
voltage sequencing between different
power supplies, the sequencing function can be implemented by controlling
the RUN pins and the PGOOD signals
with a few additional components.
Fault protection features include
overvoltage protection, over current
protection and thermal shutdown.
The LTM4608 offers some additional features. Burst Mode® operation,
pulse-skipping mode or continuous
current mode can be selected to improve light load efficiency. Burst Mode
operation provides the highest efficiency at very light load, while forced
continuous current mode leads to the
lowest output ripple. Pulse-skipping
mode offers a compromise between
Burst Mode operation and continuous
mode, offering good light load efficiency
while keeping output voltage ripple
Figure 5. Two LTM4608s are easily paralleled to provide
1.5V/16A output with interleaved switching operation.
down. Programmable output voltage
margining is supported for ±5%, ±10%
and ±15% levels. The LTM4608 also
allows frequency synchronization and
spread spectrum operation to further
reduce switching noise harmonics.
Parallel for More Power
With cycle-by-cycle current mode
control, the LTM4604 and LTM4608
can be easily paralleled to provide
more output power with excellent current sharing. The LTM4608 includes
CLKIN and CLKOUT pins to make it
DESIGN FEATURES L
possible to operate paralleled devices
out of phase of one another to reduce
input and output ripple. A total of 12
phases can be cascaded to run simultaneously with respect to each other
by programming the PHMODE pin of
each LTM4608 to different levels.
Figure 5 shows an example of two
LTM4608s in parallel to provide 16A
output current. Figure 6 shows the
measured current sharing perfor mance of the circuit, illustrating that
the DC current sharing error is less
continued on page 31
Figure 6. Bench test shows excellent current
sharing between two paralleled LTM4608s over
the entire load range.
Linear Technology Magazine • September 2008
Figure 7. Good thermal balance is maintained between two
paralleled LTM4608 boards supplying 16A output current.
29
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