LINEAR TECHNOLOGY LTM4619 Technical data
Dual µModule DC/DC Regulator Produces High Effi ciency
4A Outputs from a 4.5V to 26.5V Input
Design Note 474
Alan Chern
Dual System-in-a-Package Regulator
Systems and PC boards that use FPGAs and ASICs are
often very densely populated with components and ICs.
This dense real estate (especially the supporting circuitry
for FPGAs, such as DC/DC regulators) puts a burden on
system designers who aim to simplify layout, improve
performance and reduce component count. A new family of DC/DC μModule
®
regulator systems with multiple
outputs is designed to dramatically reduce the number
of components and their associated costs. These regulators are designed to eliminate layout errors and to offer
a ready-made complete solution. Only a few external
components are needed since the switching controllers,
dn474 F01
Figure 1. The LTM4619 LGA Package Is Only
15mm × 15mm × 2.82mm and Houses Dual
DC/DC Switching Circuitry, Inductors, MOSFETs
and Support Components
power MOSFETs, inductors, compensation and o ther support components are all integrated within the compact
surface mount 15mm × 15mm × 2.82mm LGA package.
Such easy layout saves board space and design time by
implementing high density point-of-load regulators.
The LTM
®
4619 switching DC/DC μModule converter
regulates two 4A outputs from a single wide 4.5V to
26.5V input voltage range. Each output can be set between 0.8V and 5V with a single resistor. In fact, only a
few components are needed to build a complete circuit
(see Figure 2).
Figure 2 shows the LTM4619 μModule regulator in an
application with 3.3V and 1.2V outputs. The output voltages can be adjusted with a value change in R
R
. Thus, the fi nal design requires nothing more than
SET2
SET1
and
a few resistors and capacitors. Flexibility is achieved by
pairing outputs, allowing the regulator to form different
combinations such as single input/dual independent
outputs or single input/parallel single output for higher
maximum current output.
L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and μModule are
registered trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
01/10/474
4.5V TO
26.5V
V
OUT1
1.2V/4A
10μF
s2
100μF
R
121k
SET1
22pF 22pF
0.1μF
V
IN
V
FB1
COMP1
V
OUT1
TK/SS1
RUN1
PGOOD
MODE/
INTV
PLLIN
LTM4619
SGND PGND
CC
FREQ/
PLLFLTR
V
FB2
COMP2
V
OUT2
TK/SS2
RUN2
EXTV
R
SET2
19.1k
V
OUT2
3.3V/4A
100μF
0.1μF
CC
dn474 F02
Figure 2. 4.5V to 26.5V Input to Dual 3.3V and 1.2V Outputs with 4A Maximum Output Current Each
The effi ciency of the system design for Figure 2 is shown
in Figure 3 and power loss is shown in Figure 4, both at
various input voltages. Effi ciency at light load operation
can be improved with selective pulse-skipping mode or
Burst Mode
®
operation by tying the mode pin high or
leaving it fl oating.
Multiphase Operation for Four or More Outputs
For a 4-phase, 4-rail output voltage system, use two
LTM4619s and drive their MODE_PLLIN pins with a
®
LTC
6908-2 oscillator, such that the two μModule
devices are synchronized 90° out of phase. Reference
Figure 21 in the LTM4619 data sheet. Synchronization also lowers voltage ripple, reducing the need for
high voltage capacitors whose bulk size consumes
board space. The design delivers four different output voltage rails (5V, 3.3V, 2.5V and 1.8V) all with 4A
maximum load.
Thermal Performance
Exceptional thermal performance is shown in Figure 5
where the unit is operating in parallel output mode;
single 12V
to a single 1.5V
IN
at 8A. Both outputs
OUT
tied together create a combined output current of 8A
with both channels running at full load (4A each). Heat
dissipation is even and minimal, yielding good thermal
results. If additional cooling is needed, add a heat sink on
top of the part or use a metal chassis to draw heat away.
Conclusion
The LTM4619 dual output μModule regulator makes
it easy to convert a wide input voltage range (4.5V to
26.5V) to two or more 4A output voltage rails (0.8V to
5V) with high effi ciency and good thermal dissipation.
Simplicity and performance are achieved through dual
output voltage regulation from a single package, making
the LTM4619 an easy choice for system designs needing
multiple voltage rails.
95
90
85
80
75
EFFICIENCY (%)
70
65
60
0
1
2345
CURRENT (A)
6V
12V
24V
IN
IN
IN
dn474 F03
Figure 3. Effi ciency of the Circuit in Figure 2 at Different
Input Voltage Ranges for 3.3V and 1.2V Outputs
4.0
3.5
3.0
2.5
2.0
1.5
POWER LOSS (W)
1.0
0.5
0
0
1
2345
CURRENT (A)
24V
12V
6V
IN
IN
IN
dn474 F04
Figure 4. Power Loss of the Circuit in
Figure 2 at Different Input Voltages for
3.3V and 1.2V Outputs
dn474 F05
Figure 5. LTM4619: Exceptional Thermal Performance of a Paralleled Output
μModule Regulator (12VIN to Paralleled 1.5V
Data Sheet Download
www.linear.com
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
at 8A Load)
OUT
For applications help,
call (408) 432-1900, Ext. 2593
dn474 LT/TP 1110 116K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 2009
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