LINEAR TECHNOLOGY LTM8025 Technical data
L DESIGN IDEAS
V
IN
RUN/SS
SHARE
RT ADJ
V
OUT
GND
LTM8025
VIN*
22V TO 36V
*RUNNING VOLTAGE RANGE. PLEASE REFER TO
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS
V
OUT
12V AT 3A
47.5k
34.8k
4.7µF
22µF
PGOOD
SYNC
AUX
BIAS
OUTPUT CURRENT (mA)
40
80
60
70
100
90
50
EFFICIENCY(%)
0 500 1000 1500 2000 2500 3000
VIN = 24V
V
IN
RUN/SS
SHARE
RT ADJ
V
OUT
GND
LTM8025
V
IN
3.6V TO 24V
V
OUT
1.8V AT 3A
147k
383k
10µF 300µF
PGOOD
SYNC
AUX
BIAS
BIAS
AUX
V
OUT
V
IN
GND GND
GND
THERMAL VIAS TO GND
R
T
R
ADJ
PGOOD
C
IN
C
OUT
SYNC
SHDN
Self-Contained 3A µModule Buck
Regulator Produces 0.8V–24V Output
from 3.6V–36V Input
Introduction
Ask any group of engineers, “What
would you do with a 3A DC/DC converter?” and you will probably get a
wide range of answers—from powering
a DSP rail at 1.8V to running a bank
of 24V switching I/O. Typically, these
two particular applications would
require completely different DC/DC
controller ICs and topologies. However, the LTM8025 µModule DC/DC
converter can satisfy the requirements
of these and just about any other 3A
applications.
The LTM8025 3A µModule DC/DC
buck converter operates from 3.6V to
36V inputs to produce output voltages
as low as 0.8V and as high as 24V.
Furthermore, the LTM8025 features
single cycle Burst Mode® operation,
so it is able to handle a wide range
of load currents, from no load to 3A,
with minimum ripple.
Figure 1. Layout is easy with the LTM8025.
The LTM8025 integrates the controller, control circuitry, inductor,
power switch and rectifier all into a
single IC form factor 15mm × 9mm ×
4.32mm package. This LGA package is
RoHS (e3) compliant, and features gold
pads for easy assembly in both leaded
and unleaded solder processes.
by David Ng
Easy Layout
The LTM8025’s high level of integration
simplifies the design of just about any
3A power supply. Just add two resistors, input and output capacitance to
make a complete power supply. Layout
is easy, as shown in Figure 1. Figures
2 and 3 show the schematic and efficiency of the LTM8025 producing
12V bus power from a 24V source,
while Figure 4 shows the LTM8025
producing 1.8V from an input range
of 3.6V to 36V.
Versatile Feature Set
The LTM8025 may be operated over
a wide frequency, from 200kHz to
2.4MHz, and may be synchronized to
an external clock source through the
SYNC pin. The LTM8025 start-up is
controlled through its RUN/SS pin,
which also serves to put the part into
continued on page 42
Figure 2. A complete 12V at 3A power supply requires
only the LTM8025, two capacitors and two resistors.
40
40
Figure 3. The LTM8025 boasts high efficiency.
Figure 4. The LTM8025 can produce low voltages from a wide input range.
Linear Technology Magazine • September 2009
L NEW DEVICE CAMEOS
V
IN
RUN/SS
SHARE
RT ADJ
V
OUT
GND
LTM8025
VIN*
4.1V TO 36V
V
OUT
2.5V AT 5.6A
3V
137k
113k
PGOOD
SYNC
AUX
BIAS
V
IN
RUN/SS
SHARE
RT ADJ
V
OUT
GND
LTM8025
OPTIONAL
SYNC
137k
2.2µF
2.2µF
300µF
PGOOD
SYNC
AUX
BIAS
*RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION
SECTION FOR START-UP DETAILS
NOTE: SYNCHRONIZE THE TWO MODULES TO AVOID BEAT FREQUENCIES,
IF NECESSARY. OTHERWISE, TIE EACH SYNC TO GND
The LT4356-2 is offered in 12-pin
DFN and 16-pin SO packages, while
the LT4356-3 is available in 12-pin
DFN, 16-pin SO, and 10-pin MSOP
packages.
Dual Output Synchronous
DC/DC Controller Draws Only
170µA in Battery-Powered
Systems
The LTC3868/-1 is a low quiescent
current, 2-phase dual output synchronous step-down DC/DC controller.
The LTC3868/-1 draws only 170µA
with one output active and only 300µA
when both outputs are active, making
it ideal for battery-powered applications. With both outputs shut down,
the LTC3868/-1 draws only 8µA. The
LTC3868/-1 has an input supply
range of 4V to 24V and each output can
be set from 0.8V to 14V at output currents up to 20A. With efficiency as high
as 95%, a LTC3868/-1 based DC/DC
converter is well suited for powering
industrial and medical devices, along
with portable instruments, notebook
and netbook computers.
The LTC3868/-1 operates with
a user -adjustable, fixed frequency
between 50kHz and 900kHz, and
can be synchronized to an external
clock from 75kHz to 850kHz using
its phase-locked-loop (PLL). The user
can select from continuous operation,
pulse-skipping and low ripple Burst
Mode operation during light loads.
These parts also safely start up with
a prebiased load by powering up and
down in pulse-skipping mode.
The LTC3868/-1’s 2-phase operation reduces input capacitance
requirements and its current mode
architecture provides easy loop compensation and fast transient response.
Both outputs have adjustable softstart to control the turn-on time, and
the output overload protection feature
latches off the converter until the input
voltage is recycled. The LTC3868/
LTC3868-1 also features a tight ±1.5%
reference voltage accuracy over a
–40°C to 85°C operating temperature
range. The LTC3868 is the fully featured part with additional functions
beyond the LTC3868-1 including a
clock out, phase modulation, two
power good outputs and adjustable
current limit.
The LTC3868 is offered in a 32-lead
5mm × 5mm QFN package and the
LTC3868-1 in a 28-pin SSOP or 4mm
× 5mm QFN-28 packages.
Boost & Inverting DC/DC
Converter for Active Matrix
OLED & CCD Bias
The LT3582, LT3582-5 and LT358212 dual channel DC/DC converters
that deliver both positive and negative
outputs required in many biasing applications such as active matrix OLED
(organic light-emitting diode) displays
as well as CCD (charge coupled device)
applications. The LT3582/-5/-12 offer
an I2C interface that can dynamically
program output voltages, power sequencing and output voltage ramps as
the application requires. Alternatively,
these parameters can be set in manufacturing and made permanent via
the built in nonvolatile OTP (one time
programmable) memory. The LT3582’s
positive output voltage can be set between 3.2V and 12.775 in 25mV steps,
whereas the negative output can be set
between –1.2V and –13.95V in 50mV
steps. The LT3582-5 and LT3582-12
are pre-configured with ±5V and ±12V
outputs respectively, useful in many
signal conditioning applications.
L
LTM8025, continued from page 40
a low power off state in which the part
draws less than 1µA. Furthermore,
the part comes with a PGOOD pin to
indicate that the output is within 90%
of its target voltage.
Parallel Multiple LTM8025s
for High Current Capability
The LTM8025 is equipped with a
SHARE pin to allow parallel operation
for applications requiring more than
3A load current. Figure 5 shows two
synchronized LTM8025’s providing
2.5V
at 5.6A.
OUT
Conclusion
The highly versatile LTM8025 3A
µModule DC/DC buck converter is
easy to use and fits just about any
step-down regulator need. Its wide
input and output ranges and high level
of integration reduce design effort and
associated costs.
L
Figure 5. Two LTM8025s can be operated in parallel for more than 3A load current.
42
42
Linear Technology Magazine • September 2009
Loading...