15A uModule Regulator Solves Thermal Problems by Converting 12V to 1V with High Efficiency

15A µModule Regulator Solves Thermal Problems by
Converting 12V to 1V with High Efficiency
Eddie Beville
Advances in silicon process technology continue
to reduce transistor geometries down to historical
levels in microprocessors, FPGAs and ASICs. The
power supply voltage levels necessary to power these
large, complex digital devices also continue to shrink,
creating unique power supply design challenges.
One major concern is the power regulator’s conversion efficiency at low output
voltages. For example a typical high
efficiency switching regulator that converts 12V to 3.3V at 15A has a conversion efficiency of ~93%. For practical
purposes, such a regulator incurs most
of its efficiency loss due to I2R losses.
Therefore 93% efficiency for processing
49.5W to the load equates to a 3.72W loss.
Likewise, a low output voltage requirement of 1V at 15A with an efficiency
of 76% incurs a power loss of 4.74W.
Typical high density power solutions
are challenged to achieve high efficiencies at low output voltages due to the
size constraints of the power stage. The
power stage must have high performance
system temperature, thus compromising system performance and reliability.
power MOSFETs and inductors to improve
low voltage conversion efficiency not
just an increase the solution size.
In reality, many feature-laden digital
devices have current requirements in the
>30A range for the low voltage supply. Thus a 76% efficiency 1V output
would incur a 9.48W loss for a 30A load,
which would certainly cause thermal
challenges. The thermal problems multiply with the number of 30A regulators required on a system board.
Unchecked regulator power losses,
when added to other system power
losses create serious thermal challenges. One issue is that small-geometry
ASIC or FPGA leakage currents rise with
Figure 1. A complete 1V at 15A converter requires only a few components around the LTM4627 µModule
regulator, which comes in a thermally enhanced 15mm × 15mm × 4.32mm package
One possible solution is to use a power
converter module that can deliver significantly higher output power than necessary
for the application, and run it at an output
current point that maximizes efficiency.
Of course, overly large solutions are not
feasible in space-constrained systems
and the current limit of this solution is
much higher than the required current.
Another solution is to use a discrete
power converter that is optimized for low
output voltage efficiency. But again space
constraints and component sourcing can
be challenging. Another challenge with a
discrete design is how to effectively cool it
and heat sink the various discrete power
components, which have different heights.
µMODULE SOLUTION
Figure 1 shows a complete 1.0V at 15A converter that uses the LTM4627 µModule
regulator housed in a 15mm × 15mm
× 4.32mm package. The LTM4627 integrates the high performance power path
Figure 2. Efficiency of the regulator in Figure 1
100
22µF
16V
×3
VOUT = 1V
fSW = 400kHz
95
10k
VIN
EXTVCC INTVCC PGOOD
RUN
VOUT
fSET
VOUT_LCL
COMP
150pF
100k
0.1µF
LTM4627
DIFF_OUT
TRACK/SS
VOSNS+
MODE_PLLIN
VOSNS–
SGND
38 | October 2011 : LT Journal of Analog Innovation
PGND
COUT1
470µF
6.3V
VFB
82pF
+
COUT2
100µF
6.3V
VOUT
1V
15A
90
EFFICIENCY (%)
VIN
4.5V TO 16V
85
80
75
70
RFB
90.9k
VIN = 5V
VIN = 8V
VIN = 12V
65
60
0
3
6
9
ILOAD (A)
12
15
design ideas
6% to 7% over typical (and larger)
solutions, or a power loss improvement of 1.68W in a small form factor.
16
OUTPUT CURRENT (A)
Figure 3 shows a LTM4627 thermal plot
for 12V to 1V at 15A with no airflow or
heat sinking. The temperature rise is ~40°C
above 25°C ambient at 65°C. The power
loss of ~3W multiplied by the data sheet
specified θJA thermal resistance of 13°C/W
matches the 40°C rise in the thermal plot.
Figure 3. Thermal plot of the LTM4627 converting
12V to 1V at 15A with no forced air or heat sink
The LTM4627 features include fully differential remote sensing, output voltage
tracking and soft-start, high efficiency
at light loads utilizing the Burst Mode
operation or pulse-skipping features,
voltage monitoring and frequency
synchronization. The LTM4627 uses
a current mode architecture, which
enables multiple µModule regulators
to run in parallel (Figure 5), sharing
the load for increased output current
with accurate current limit control.
10
VIN
The LTM4627 µModule regulator is a high
performance versatile DC/DC converter
that can be used in many applications
requiring high efficiency over a wide
output voltage range. The very small form
factor and ease of use make the LTM4627
ideal for space-constrained designs. n
VOUT
1V
30A
MODE_PLLIN
VOSNS–
SGND
GND
+
150pF
470µF
6.3V
DIFF_OUT
VOSNS+
100µF
6.3V
VFB
270pF
22µF
16V
×3
VIN
EXTVCC INTVCC PGOOD
COMP
VOUT
TRACK/SS
RUN
INTVCC
200k
LTM4627
VOUT_LCL
fSET
100k
MOD
60 70 80 90 100 110 120
AMBIENT TEMPERATURE (ºC)
VOUT
TRACK/SS
CLOCK SYNC
0˚ PHASE
SET
50
EXTVCC INTVCC PGOOD
RUN
OUT1
LTC6908-1
OUT2
GND
40
CONCLUSION
COMP
10k
1µF
0LFM, NO HEATSINK
200LFM, NO HEATSINK
400LFM, NO HEATSINK
INTVCC
22µF
16V
×3
V+
4
Current sharing is well balanced during
both steady state DC load and dynamic
transients. The accurate remote sense
amplifier yields outstanding voltage accuracy at the load point. For even higher output currents, simply add more LTM4627s.
VIN
7V TO 16V
Figure 5. A 2-phase, 30A design based on two parallel
LTM4627 µModule regulators clocked 180° out-of-phase.
For higher output currents, simply add more LTM4627s.
6
Figure 4. Derating curves for the
LTM4627 converting 12V to 1V
Figure 5 shows a 2-phase, 30A design utilizing two parallel LTM4627 µModule regulators that are clocked 180° out-of-phase
using clock signals from the LTC6908-1.
0.1µF
8
0
Figure 4 shows the LTM4627 12V to 1V derating curve. The LTM4627 can operate in
higher ambient temperatures with full load
capability in a very small form factor.
The LTM4627 µModule regulator is
optimized for high efficiency conversion
to low output voltages—with a complete
converter packaged in a small, thermally
enhanced form factor. The input voltage range is 4.5V to 20V with output
voltage programming from 0.8V to 5V.
Figure 2 shows efficiencies of 82% to 83%
for 1V at 15A from 5V, 8V and 12V inputs.
This is an efficiency improvement of
12
2
The LTM4627 package has a highly thermal
conductive substrate with a layout that
is thermally modeled and designed to
enhance thermal performance and uniform heat spreading. While the package
is small, it presents enough surface area
to a PCB (and heat sink) to minimize the
overall thermal resistance of the solution.
and control circuitry, thus simplifying the design to a few external bulk
capacitors and a few small resistors.
VIN = 12V
VOUT = 1V
14
CLOCK SYNC
180˚ PHASE
100k
LTM4627
VOUT_LCL
DIFF_OUT
fSET
VOSNS+
MODE_PLLIN
VOSNS–
SGND
GND
+
VFB
470µF
6.3V
100µF
6.3V
INTVCC
RFB1
45.3k
October 2011 : LT Journal of Analog Innovation | 39
Similar pages