Page 1
DESIGN IDEAS L
RT
SHARE
V
IN
FIN
1µF
22µF
78.7k48.7k
V
OUT
3.3V
1A
RUN/SS
V
IN
4.75V TO 36V*
PGOOD
BIAS
LTM8031
AUX
OUT
SYNC GND ADJ
*RUNNING VOLTAGE RANGE
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 10V
I
LOAD
= 1A
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 5V
I
LOAD
= 1A
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 2.5V
I
LOAD
= 1A
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
EMI Certified Step-Down Converter
in 15mm × 9mm µModule Package
Produces 1A, 0.8V
3.6V
IN –
Introduction
The LTM8031 is a low noise DC/DC
step-down µModule regulator that
operates from input voltages from 3.6V
to 36V and is independently certified
to be compliant with the stringent
requirements of EN55022 class B.
Its output can be programmed to
provide voltages from 0.8V to 10V at
up to 1A. A nearly complete converter
solution is contained in the 15mm ×
9mm × 2.82mm package. As seen in
Figure 1, the LTM8031 just requires
one resistor to set the output voltage,
another resistor to set the operating
frequency, and some input and output
capacitance.
LTM8031 Features
The LTM8031 comes with many of
the features often required in modern
power supplies. It can be sequenced
via its RUN/SS pin, which also serves
to allow the user to control the output
behavior at turn on. A PGOOD pin
indicates when the output is within
10% of the target regulation voltage.
The SYNC pin is used to synchronize
the LTM8031 to a desired system
frequency.
36V
IN
Figure 1. The LTM8031 needs just two resistors and some capacitance to get it running.
Product VIN Range V
LTM8020 4V to 36V 1.25V to 5V 200mA
LTM8021 3.6V to 36V 0.8V to 5V 500mA
LTM8031 3.6V to 36V 0.8V to 10V 1A
LTM8032 3.6V to 36V 0.8V to 10V 2A
Through the incorporation of a high
Q pi filter and electromagnetic inter ference reduction design techniques,
the LTM8031 is purpose built with low
radiated emissions in mind. It has been
independently verified to be compliant with EN55022:2006 (Information
OUT
–10V
OUT
from
by David Ng
Table 1. Low noise µModule DC/DC step down converters
Range I
OUT
Technology Equipment – Radio Disturbance Characteristics – Limits and
Methods of Measurement). EN55022
has two classes, A and B. The LTM8031
is certified compliant with class B,
the more stringent of the two. More
than that, the LTM8031 beats the
LOAD(MAX)
continued on page 38
Figure 2. The LTM8031 meets EN55022 Class
B while producing 10V
Linear Technology Magazine • December 2009
at 1A from 36VIN.
OUT
Figure 3. The LTM8031 is EN55022 Class B
compliant with 5V
at 1A from 36VIN.
OUT
Figure 4. The LTM8031 beats the EN55022
Class B limits by a wide margin with 2.5V
at 1A from 36VIN.
OUT
3131
Page 2
L NEW DEVICE CAMEOS
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 5V
I
LOAD
= 500mA
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 10V
I
LOAD
= 2A
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
EMISSIONS LEVEL (dBµV/m)
FREQUENCY (MHz)
10000
90
–10
200 400 600 800
0
10
20
30
40
50
60
70
80
VIN = 36V
V
OUT
= 5V
I
LOAD
= 200mA
CISPR22 CLASS B STANDARD
TWO EMISSIONS TRACES:
HORIZONTAL AND VERTICAL
ANTENNA ORIENTATIONS
MEASURED EMISSIONS
New Device Cameos
Low Voltage Hot Swap
Controllers Provide
Extended Fault Timers
The LTC4215-2 and LTC4215-3 are
low voltage Hot Swap™ controllers with
onboard ADCs and I2C compatible interfaces. Functionally, the LTC4215-2
and LTC4215-3 are similar to the
LTC4215 and LTC4215-1, respectively, with the overcurrent fault timers
extended from 20µs to 420µs.
Some Hot Swap applications require
more than the 20µs overcurrent fault
filter time provided by the LTC4215
and LTC4215-1. For example, some
loads draw brief surge currents and
fast input voltage steps cause high
transient charging currents into bulk
output capacitance. Increasing the
overcurrent fault filter time from 20µs
to 420µs allows applications to ride out
such current surges, while still turning
off before MOSFET safe operating area
limits have been reached.
The LTC4215-2 also defaults
to auto-retry after experiencing
an overcurrent fault, making the
LTC4215-2 the only part in the
LTC4215 family that will auto-retry by
default after an overcurrent fault.
The LTC4215-2 and LTC4215-3
work in applications from 12V (with
transients to 24V) down to 3.3V and
are available in 4mm × 5mm QFN
packages.
Isolated RS485 µModule
Transceiver Integrates
Isolated Power
The LTM2881 is an isolated RS485
µModule transceiver that guards
against large ground-to-ground differentials and common mode transients.
In practical RS485 systems, ground
potentials vary widely from node to
node, often exceeding the tolerable
range, which can result in an interruption of communications or destruction
of a transceiver. The LTM2881 breaks
ground loops by isolating the logic level
interface and line transceiver using
internal inductive signal isolation that
allows for a much larger common mode
voltage range plus superior common
mode rejection of >30kV/µs. A low
EMI DC/DC converter powers the
transceiver and provides an isolated
5V supply output for powering any
supporting external components.
With 2,500V
of galvanic isola-
RMS
tion, onboard secondary power and
a fully compliant RS485 transmitter
and receiver, the LTM2881 requires
no external components, ensuring a
complete, compact µModule solution
for isolated serial data communications.
Two versions of the LTM2881 are
available for 3.3V and 5V input supplies, in low profile 11.25 × 15mm ×
2.8mm surface mount LGA and BGA
packages.
L
LTM8031, continued from page 31
EN55022B limits by a wide margin,
better than 20dB in some bands. This
is shown in Figures 2, 3 and 4, where
the LTM8031 is operated from 36V
produce 10V
at 1A, respectively. The 36VIN, 10V
at 1A configuration is a worst case
radiated emissions scenario, because
the LTM8031 is operating with both
maximum rated switching voltage and
output power.
Figure 5. The LTM8020 is our quietest EMC
µModule converter, providing 5V at 200mA
from 36V
38
38
IN.
OUT
, 5V
OUT
and 2.5V
The LTM8031 is rated to provide
1A, but what about other load currents? Linear Technology offers three
to
other EN55022 class B compliant
IN
µModule DC/DC converters, as
OUT
well: the LTM8020 for 200mA loads,
OUT
the LTM8021 for 500mA, and the
LTM8032 for 2A loads. These are
summarized in Table 1, and the worst
case emissions for each are given in
Figures 5, 6, and 7, respectively
Figure 6. The LTM8021 is another EN55022B
compliant device, capable of outputting 5V at
500mA from 36VIN.
Conclusion
It is not uncommon to have to design a
power system that requires numerous
power rails at different load currents,
low radiated emissions, and small
size. For ease of design, take a look
at the LTM8031 and its family of low
noise µModule DC/DC step-down
converters.
Figure 7. The LTM8032, weighing in at 10V
at 2A from 36VIN, meets EN55022 class B.
Linear Technology Magazine • December 2009
L
OUT
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