Complete 20V, 20A High Performance µModule DC/DC Regulator in 15mm × 15mm × 4.32mm Package

Complete 20V, 20A High Performance µModule DC/DC
Regulator in 15mm × 15mm × 4.32mm Package
Sam Young
The LTM4637 is a complete 20A high efficiency switch mode power supply
in a compact 15mm × 15mm × 4.32mm LGA package. The controller, power
MOSFETs, inductor and compensation circuitry are all integrated within its low
profile package, allowing use on the bottom side of the PCB. The LTM4637 has
an input voltage range of 4.5V to 20V and supports an output voltage range of
0.6V to 1.8V. It has an operating frequency range of 440kHz–770kHz where it
can provide up to 20A with just a few additional external components.
VERSATILITY
The LTM4637 features a programmable
soft-start to limit inrush currents as well
as output voltage tracking for sequencing requirements. Also included are an
output voltage power good indicator, an
external VCC pin allowing for bypassing
of the internal LDO for an extra efficiency benefit, selectable pulse-skipping
mode and Burst Mode operation for
increased light load efficiency, as well
as internal temperature monitoring.
EASY COMPENSATION;
EASY PARALLEL OPERATION
The LTM4637’s constant-frequency current
mode control and internal feedback loop
compensation provide excellent stability and transient performance for a wide
range of output capacitors. The LTM4637
also includes an internal differential
remote sense amplifier, as well as a phase
locked loop and voltage controlled oscillator for synchronization to an external
clock. These features make the LTM4637
ideal for paralleling modules to satisfy
even higher load current demands. The
current mode control architecture of the
LTM4637 ensures balanced load current
sharing to maximize efficiency and thermal benefits. The differential remote sense
30 | January 2014 : LT Journal of Analog Innovation
amplifier allows for paralleled LTM4637s
to regulate a precise output voltage
±1.5% at the point-of-load, compensating for error caused by PCB IR voltage
drops. The internal phase locked loop
allows synchronization and interleaving
of paralleled phases, minimizing voltage and current ripple in the system.
the overvoltage condition is cleared. In
the event of an output short-circuit, if the
output voltage falls 50% below its nominal output level, the maximum output current is progressively lowered to one-third
of the original value, limiting the current
dumped into the short. The overtemperature protection shuts down the internal
controller at ~130°C–137°C, restarting the
controller again when the temperature
cools. These protection features help
ensure a low risk design. Furthermore, the
LTM4637’s dependability can be assured
by rigorous electrical and reliability
testing performed on each module.
PROTECTION
The LTM4637 features overvoltage protection, foldback current protection and
overtemperature protection. In the event
of an overvoltage condition where the
output voltage exceeds 10% of the programmed value, the top MOSFET is forced
off and bottom MOSFET is turned on until
Figure 1. Complete 1.8V, 20A regulator requires only a few components
12V
CIN
22µF
25V
×2
0.1µF
124k
VIN
EXTVCC INTVCC PGOOD
COMP
VOUT
TRACK/SS
VOUT_LCL
RUN
DIFF_OUT
LTM4637
fSET
VOSNS+
MODE_PLLIN
VOSNS–
TEMP
SGND
GND
VFB
+
82pF
RFB
30.1k
470µF
2.5V
100µF
6.3V
X5R
×2
VOUT
1.8V
20A
design ideas
The LTM4637 is a complete POL power supply solution for applications that
require top-notch performance in a small footprint with minimal design effort
and user-adjustable feature versatility. Its low power loss and thermal resistance
allow for up to 20A of load current per phase, while its current mode structure
allows the load current to be scaled up via parallel configurations.
Figure 2. Efficiency of the 1.8V regulator in Figure 1
Figure 3. Thermal scan of the LTM4637 under full
load for the solution in Figure 1.
95
EFFICIENCY (%)
90
85
80
75
70
65
0
2
4
6
8 10 12 14 16 18 20
ILOAD (A)
MINIMAL DESIGN EFFORT
Little effort is required to create a high
performance design because a complete power supply solution is integrated into the LTM4637. Just a few
external components are required to
conclude an application’s design, simplifying the schematic and PCB layout.
For example, set the output voltage and
switching frequency each with a single
resistor from their respective programming pins to ground, then select input
and output capacitors to satisfy voltage
and current ripple requirements and the
base design is complete. The LTM4637
minimizes total design effort, an important
factor when time to market is important
or limited power design resources are
available. Figures 1 and 2 show a typical
12V input to 1.8V, 20A output application circuit and its efficiency, exemplifying the simplicity and high performance
benefits of designing with the LTM4637.
TA = 25°C, NO AIR, NO HEAT SINK
ILOAD = 20A, VIN = 12V, VOUT = 1.8V
EXCEPTIONAL THERMAL
PERFORMANCE
Exceptional thermal performance allows
for increased current capability, which
translates to a reduced total solution cost
and increased reliability in high current density applications. The LTM4637
can provide up to 20A while remaining
cool due to low power dissipation and
thermal resistances. Figure 3 shows the
µModule regulator’s outstanding thermal
performance for the setup in Figure 1.
Even while providing a hefty 20A of load
current, with no forced air cooling, the
LTM4637 easily provides 36W of high current output power all from a footprint of
less than 0.35in2 without risking thermal overload. Attach a heat sink to the
exposed metal on the top of the package
and add forced airflow conditions for
further reduction of internal temperatures.
CONCLUSION
The LTM4637 is a complete POL power
supply solution for applications that
require top-notch performance in a small
footprint with minimal design effort and
user-adjustable feature versatility. Its low
power loss and thermal resistance allow
for up to 20A of load current per phase,
while its current mode structure allows the
load current to be scaled up via parallel
configurations. Its built-in protection features and rigorous factory electrical testing
ensure a reliable, low risk solution. n
January 2014 : LT Journal of Analog Innovation | 31
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