+INPUT
(2)
COMMON
(3)
PWM
CONTROLLER
CURRENT
SENSE
REFERENCE &
ERROR AMP
V
CC
ON/OFF
CONTROL
(1)
V
OUT
TRIM
(5)
+OUTPUT
(4)
+SENSE
(6)
COMMON
(3)
Figure 1. Simplifi ed Schematic
SIMPLIFIED SCHEMATIC
LSM Series W3 SMT’s (surface-mount
packages) are ideal building blocks for
emerging, on-board power-distribution
schemes in which isolated 3 to 5.5V buses
deliver power to any number of non-iso-
lated, step-down buck regulators. LSM W3
DC/DC’s accept 3 to 5.5 Volts and convert
it, with the highest effi ciency in the smallest
space, to a 0.75, 1, 1.2, 1.5, 1.8, 2, 2.5, or
3.3 Volt output fully rated at 16 Amps.
LSM W3’s are ideal point-of-use/load
power processors. They typically require
no external components. Their surface-
mount packages occupy a mere 1.3" x 0.53"
(33.0 x 13.5mm), and are only 0.34 inches
(8.6mm) high.
The LSM’s best-in-class power density is
achieved with a fully synchronous, fi xed-
frequency, buck topology that also delivers:
high effi ciency (97%, 3.3VOUT, 8A), low noise
(30mVp-p typ.), tight line/load regulation
(±0.1%/±0.25% max.), quick step response
(30μsec), stable no-load operation, and no
output reverse conduction.
The fully functional LSM’s feature output
overcurrent detection, continuous short-
circuit protection, over-temperature protec-
tion, a remote on/off control pin (pull low to
disable), an output-voltage trim function,
and a sense pin. High effi ciency enables the
LSM W3’s to deliver rated output currents of
16 Amps at ambient temperatures to +65°C
with natural convection.
If your new system boards call for mul-
tiple supply voltages, check out the econom-
ics of on-board 3-5.5V distributed power. If
you don’t need to pay for multiple isolation
barriers, DATEL’s non-isolated LSM W3
SMT’s will save you money.
PRODUCT OVERVIEW
FEATURES
Step-down, wide input buck regulators for
distributed 3-5V power architectures
3V to 5V wide-input range
0.75/1/1.2/1.5/1.8/2/2.5/3.3VOUT @16A
Non-isolated, fi xed-frequency,
synchronous-rectifi er topology
Tape and reel SMT package
±1% setpoint accuracy
Effi ciencies to 95% @ 16 Amps
Noise as low as 30mVp-p
Stable no-load operation
Remote on/off control
Sense pin and output voltage trim
No derating to +65°C with no fan
Designed to meet UL/IEC/EN60950-1 safety
EMC compliant
Non-Isolated, 3-5.5V
IN
,
0.75-3.3V
OUT
16 Amp
DC/DC’s in SMT Packages
Typical unit
Typical topology is shown.
FEATUR
E
ES
Typ
ic
ica
lu
NOT RECOMMENDED
FOR NEW DESIGNS
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 1 of 12
For full details go to
www.murata-ps.com/rohs
www.murata-ps.com
www.murata-ps.com/support
Pin Function P63
1 On/Off Control
2 +Input
3 Common
4 +Output
5 VOUT Tr i m
6 +Sense
I/O Connections
➀ Typical at TA = +25°C under nominal line voltage and full-load conditions, unless noted. All models
are tested/specifi ed with external 22μF tantalum input and output capacitors. These capacitors
are necessary to accommodate our test equipment and may not be required to achieve specifi ed
performance in your applications. See I/O Filtering and Noise Reduction.
➁ Ripple/Noise (R/N) is tested/specifi ed over a 20MHz bandwidth and may be reduced with external
fi ltering. See I/O Filtering and Noise Reduction for details.
➂ These devices have no minimum-load requirements and will regulate under no-load conditions.
Regulation specifi cations describe the output-voltage deviation as the line voltage or load is varied
from its nominal/midpoint value to either extreme.
➃ Nominal line voltage, no-load/full-load conditions.
➄ VIN = 4.5 Volts minimum for VOUT = 3.3 Volts.
➅ LSM-T/16-W3 specs are given with VOUT = 3.3 Volts, unless noted.
MECHANICAL SPECIFICATIONS
PART NUMBER STRUCTURE
Performance Specifi cations and Ordering Guide➀
Case C45
3-4#/00%2,%!$3
#/0,!.!2
"/44/-6)%7
2%#/--%.$%$0!$,!9/54
490
490
%130
2ECOMMENDED0AD3IZEXX
%130
Maximum Rated Output
Current in Amps
Non-Isolated SMT
Output
Confi guration:
L = Unipolar
Low Voltage
Nominal Output Voltage:
0.75, 1, 1.2, 1.5, 1.8, 2, 2.5, 3.3
or 0.75-3.3 (T) Volts
Input Voltage Range:
W3 = 3 to 5.5 Volts
(5V nominal)
L SM 16-/W3-1.8
BOTTOM VIEW
1.36
(34.54)
0.375
(9.53)
0.112 TYP.
(2.84)
0.052
(1.32)
LSMWITH REMOVEABLE HEAT SHIELD
FOR HIGHTEMPERATURE SOLDER
CAUTION
PRESS TO REMOVE
THE HEAT SHIELD
AFTER THE SOLDER
PROCESS
0.60
(15.24)
0.049
(1.24)
0.310
(7.87)
0.010
(0.254)
0.55
(13.97)
0.052
(1.32)
0.062
(1.57)
0.047
(1.19)
0.570 (14.48)
3EQ.SP.@
0.190 (4.83)
2
3456
1
NOTCH IN SHELL
INDICATES PIN ONE
Refer to the last page for
Tape and Reel information.
Model
VOUT
(Volts)
IOUT
(Amps)
R/N (mVp-p) ➁Regulation (Max.) ➂
VIN Nom
(Volts)
Range
(Volts)
IIN ➃
(mA/A)
Effi ciency (Full Load)
VIN = nom. VIN = min.
Min. Typ. Typ.
Package
(Case
Pinout)Typ. Max. Line Load
LSM-0.75/16-W3 0.75 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/2.98 80% 82% 81.5% C45, P63
LSM-1/16-W3 1 16 30 45 ±0.125% ±0.15% 5 3-5.5 70/3.72 85% 86% 86.5% C45, P63
LSM-1.2/16-W3 1.2 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/4.36 85.75% 86.5% 88.0% C45, P63
LSM-1.5/16-W3 1.5 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/5.33 88% 88.8% 90.0% C45, P63
LSM-1.8/16-W3 1.8 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/6.30 89.5% 91.5% 92% C45, P63
LSM-2/16-W3 2 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/6.92 90.5% 92.5% 92.5% C45, P63
LSM-2.5/16-W3 2.5 16 30 50 ±0.1% ±0.25% 5 3-5.5 70/8.56 91.5% 93.5% 94% C45, P63
LSM-3.3/16-W3 3.3 16 30 50 ±0.1% ±0.25% 5 4.5-5.5➄50/11.12 93% 95% 95% C45, P63
LSM-T/16-W3 ➅0.75-3.3 16 30 50 ±0.1% ±0.25% 5 3-5.5➄50/11.12 93% 95% 95.5% C45, P63
Output Input
DIMENSIONS IN INCHES (mm)
C
-
RoHS-6 hazardous
substance compliant*
* Contact Murata-PS for availability.
Third Angle Projection
Dimensions are in inches (mm shown for ref. only).
Components are shown for reference only.
Tolerances (unless otherwise specified):
.XX ± 0.02 (0.5)
.XXX ± 0.010 (0.25)
Angles ± 2˚
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 2 of 12
www.murata-ps.com/support
Input
Input Voltage Range 3-5.5 Volts (5V nominal) ➇
Input Current:
Normal Operating Conditions See Ordering Guide
Inrush Transient 0.02A2 sec
Standby/Off Mode 8mA
Output Short-Circuit Condition ➁ 60-110mA average (model dependent)
Input Refl ected Ripple Current ➁ ➅ 10-70mAp-p, model dependent
Input Filter Type Capacitive
Overvoltage Protection None
Reverse-Polarity Protection None
Undervoltage Shutdown None
On/Off Control ➁ ➂ On = open to +VIN (internal pull-up to +VIN)
Off = 0 to +0.4V (1mA)
Output
VOUT Accuracy (50% load) ±1.5%
Temperature Coeffi cient ±0.02%/°C
Minimum Loading ➀ No load
Maximum Capacitive Load 5000μF (electrolytic),
2000μF (0.02: ESR, OSCON)
VOUT Trim Range r10% ➆
Ripple/Noise (20MHz BW) ➀ ➁ ➃ See Ordering Guide
Total Accuracy 3% over line/load/temperature
Effi ciency See Ordering Guide
Overcurrent Detection and Short-Circuit Protection: ➁
Current-Limiting Detection Point 19-30 Amps (model dependent)
Short-Circuit Detection Point 98% of VOUT set
SC Protection Technique Hiccup with auto recovery
Short-Circuit Current 600mA average
Dynamic Characteristics
Transient Response (50% load step) 30-70μsec to ±2% of fi nal value
(model dependent)
Start-Up Time: ➁
VIN to VOUT and On/Off to VOUT 7msec
Switching Frequency 300 ±50kHz
Environmental
Calculated MTBF ➄ TBD
Operating Temperature: (Ambient) ➁ –40 to +85°C (with derating)
See Derating Curves
Maximum PC Board Temperature +100°C
Thermal Shutdown +115°C (110 to 125°C)
EMI
Conducted or radiated, Class B
FCC Part 15, EN55022
Safety Designed to meet UL/IEC/EN60950-1,
CSA-C22.2 No. 234
Physical
Dimensions 1.3" x 0.53" x 0.34" (33.03 x 13.46 x 8.64)
Pin Dimensions/Material 0.112" x 0.062" (2.84 x 1.57mm) rectangular
copper with gold plate over nickel underplate
Weight 0.28 ounces (7.8g)
Flamability Rating UL94V-0
Performance/Functional Specifi cations
Typical @ TA = +25°C under nominal line voltage, 200 lfm air fl ow, and full-load conditions
unless noted. ➀
➀ All models are tested/specifi ed with external 22μF tantalum input and output capacitors.These
capacitors are necessary to accommodate our test equipment and may not be required to achieve
specifi ed performance in your applications. All models are stable and regulate within spec under
no-load conditions.
➁ See Technical Notes and Performance Curves for details.
➂ The On/Off Control (pin 1) is designed to be driven with open-collector logic or the application of
appropriate voltages (referenced to Common, pin 3). Applying a voltage to On/Off Control when no input
voltage is applied to the converter may cause permanent damage.
➃ Output noise may be further reduced with the installation of additional external output fi ltering. See
I/O Filtering and Noise Reduction.
➄ MTBF’s are calculated using Telcordia SR-332(Bellcore), ground fi xed, TA = +25°C, full power,
natural convection, +67°C pcb temperature.
➅ Input Ripple Current is tested/specifi ed over a 5-20MHz bandwidth with an external 2 x 100μF input
capacitor and a simulated source impedance of 1000μF and 1μH. See I/O Filtering, Input Ripple
Current, and Output Noise for details.
➆ LSM-0.75/16-W3 can not be trimmed down.
➇ Input voltage must be 4.5V minimum for 3.3V output.
TECHNICAL NOTES
Input Voltage:
Continuous or transient 6 Volts (0.75, 1, 1.2, 1.5, 1.8, 2, 2.5 VOUT)
7 Volts (3.3VOUT and "T" models)
On/Off Control (Pin 1) +VIN
Input Reverse-Polarity Protection None
Output Overvoltage Protection None
Output Current Current limited. Devices can
withstand sustained output short
circuits without damage.
Storage Temperature –40 to +125°C
Lead Temperature See Refl ow Solder Profi le
These are stress ratings. Exposure of devices to any of these conditions may adversely
affect long-term reliability. Proper operation under conditions other than those listed in the
Performance/Functional Specifi cations Table is not implied.
Absolute Maximum Ratings
I/O Filtering and Noise Reduction
All models in the LSM W3 Series are tested and specifi ed with external 22μF
tantalum input and output capacitors. These capacitors are necessary to
accommodate our test equipment and may not be required to achieve desired
performance in your application. The LSM’s are designed with high-quality,
high-performance internal I/O caps, and will operate within spec in most appli-
cations with no additional external components.
In particular, the LSM’s input capacitors are specifi ed for low ESR and are fully
rated to handle the units’ input ripple currents. Similarly, the internal output
capacitors are specifi ed for low ESR and full-range frequency response.
In critical applications, input/output ripple/noise may be further reduced using
fi ltering techniques, the simplest being the installation of external I/O caps.
External input capacitors serve primarily as energy-storage devices. They
minimize high-frequency variations in input voltage (usually caused by IR drops
in conductors leading to the DC/DC) as the switching converter draws pulses of
current. Input capacitors should be selected for bulk capacitance (at appropri-
ate frequencies), low ESR, and high rms-ripple-current ratings. The switching
nature of modern DC/DC’s requires that the dc input voltage source have low
ac impedance at the frequencies of interest. Highly inductive source imped-
ances can greatly affect system stability. Your specifi c system confi guration
may necessitate additional considerations.
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 3 of 12
www.murata-ps.com/support
Safety Considerations
LSM W3 SMT’s are non-isolated DC/DC converters. In general, all DC/DC’s
must be installed, including considerations for I/O voltages and spac-
ing/separation requirements, in compliance with relevant safety-agency
specifi cations (usually UL/IEC/EN60950-1).
In particular, for a non-isolated converter’s output voltage to meet SELV
(safety extra low voltage) requirements, its input must be SELV compliant.
If the output needs to be ELV (extra low voltage), the input must be ELV.
Input Overvoltage and Reverse-Polarity Protection
LSM W3 SMT Series DC/DC’s do not incorporate either input overvoltage or
input reverse-polarity protection. Input voltages in excess of the speci-
fi ed absolute maximum ratings and input polarity reversals of longer than
“instantaneous” duration can cause permanent damage to these devices.
Start-Up Time
The VIN to VOUT Start-Up Time is the interval between the time at which a
ramping input voltage crosses the lower limit of the specifi ed input voltage
range and the fully loaded output voltage enters and remains within its
specifi ed accuracy band. Actual measured times will vary with input source
impedance, external input capacitance, and the slew rate and fi nal value of
the input voltage as it appears to the converter.
The On/Off to VOUT Start-Up Time assumes the converter is turned off via
the On/Off Control with the nominal input voltage already applied to the
converter. The specifi cation defi nes the interval between the time at which
the converter is turned on and the fully loaded output voltage enters and
remains within its specifi ed accuracy band. See Typical Performance
Curves.
Remote Sense
LSM
W3
SMT Series DC/DC converters offer an output sense function on pin
6.
The sense function enables point-of-use regulation for overcoming mod-
erate IR drops in conductors and/or cabling. Since these are non-isolated
devices whose inputs and outputs usually share the same ground plane,
sense is provided only for the +Output.
The remote sense line is part of the feedback control loop regulating the
DC/DC converter’s output. The sense line carries very little current and
consequently requires a minimal cross-sectional-area conductor. As such,
it is not a low-impedance point and must be treated with care in layout and
cabling. Sense lines should be run adjacent to signals (preferably ground),
and in cable and/or discrete-wiring applications, twisted-pair or similar
techniques should be used. To prevent high frequency voltage differences
between VOUT and Sense, we recommend installation of a 1000pF capacitor
close to the converter.
The sense function is capable of compensating for voltage drops between
the +Output and +Sense pins that do not exceed 10% of VOUT.
[VOUT(+) – Common] – [Sense(+) – Common] ≤ 10%VOUT
Power derating (output current limiting) is based upon maximum output
current and voltage at the converter’s output pins. Use of trim and sense
functions can cause the output voltage to increase, thereby increasing
output power beyond the LSM’s specifi ed rating. Therefore:
(VOUT at pins) x (IOUT) ≤ rated output power
Output ripple/noise (also referred to as periodic and random deviations or
PARD) may be reduced below specifi ed limits with the installation of additional
external output capacitors. Output capacitors function as true fi lter elements
and should be selected for bulk capacitance, low ESR, and appropriate fre-
quency response. Any scope measurements of PARD should be made directly
at the DC/DC output pins with scope probe ground less than 0.5" in length.
Figure 3. Measuring Output Ripple/Noise (PARD)
C1
C1 = NA
C2 = 22μF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2 R
LOAD
6
4
COPPER STRIP
3
COPPER STRIP
SCOPE
+OUTPUT
COMMON
+SENSE
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Figure 2. Measuring Input Ripple Current
All external capacitors should have appropriate voltage ratings and be located
as close to the converters as possible. Temperature variations for all relevant
parameters should be taken into consideration
The most effective combination of external I/O capacitors will be a function
of your line voltage and source impedance, as well as your particular load
and layout conditions. Our Applications Engineers can recommend potential
solutions and discuss the possibility of our modifying a given device’s internal
fi ltering to meet your specifi c requirements. Contact our Applications Engineer-
ing Group for additional details.
Input Fusing
Most applications and or safety agencies require the installation of fuses at the
inputs of power conversion components. The LSM W3 Series are not internally
fused. Therefore, if input fusing is mandatory, either a normal-blow or a
fast-blow fuse with a value no greater than twice the maximum input current
should be installed within the ungrounded input path to the converter.
As a rule of thumb however, we recommend to use a normal-blow or slow-
blow fuse with a typical value of about twice the maximum input current,
calculated at low line with the converter’s minimum effi ciency.
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 4 of 12
www.murata-ps.com/support
Output Overcurrent Detection
Overloading the power converter’s output for an extended time will invariably
cause internal component temperatures to exceed their maximum ratings and
eventually lead to component failure. High-current-carrying components such
as inductors, FET’s and diodes are at the highest risk. LSM W3 SMT Series
DC/DC converters incorporate an output overcurrent detection and shutdown
function that serves to protect both the power converter and its load.
If the output current exceeds it maximum rating by typically 50% (24 Amps) or
if the output voltage drops to less than 98% of it original value, the LSM W3’s
internal overcurrent-detection circuitry immediately turns off the converter,
which then goes into a “hiccup” mode. While hiccupping, the converter will
continuously attempt to restart itself, go into overcurrent, and then shut down.
Under these conditions, the average output current will be approximately
400mA, and the average input current will be approximately 40mA. Once the
output short is removed, the converter will automatically restart itself.
Output Voltage Trimming
Allowable trim ranges for each model in the LSM W3 SMT Series are ±10%.
Trimming is accomplished with either a trimpot or a single fi xed resistor. The
trimpot should be connected between +Output and Common with its wiper
connected to the Trim pin as shown in Figure 6 below.
A trimpot can be used to determine the value of a single fi xed resistor which
can then be connected, as shown in Figure 7, between the Trim pin and
+Output to trim down the output voltage, or between the Trim pin and Common
to trim up the output voltage. Fixed resistors should have absolute TCR’s less
than 100ppm/°C to ensure stability.
The equations below can be starting points for selecting specifi c trim-resistor
values. Recall, untrimmed devices are guaranteed to be ±1% accurate.
Adjustment beyond the specifi ed ±10% adjustment range is not recommended.
When using trim in combination with Remote Sense, the maximum rated power
must not be exceeded (see Remote Sense).
The internal 10.5Ω resistor between +Sense and +Output (see Figure 1)
serves to protect the sense function by limiting the output current fl owing
through the sense line if the main output is disconnected. It also prevents
output voltage runaway if the sense connection is disconnected.
Note: If the sense function is not used for remote regulation, +Sense
(pin 6) must be tied to +Output (pin 4) at the DC/DC converter pins.
On/Off Control
The On/Off Control pin may be used for remote on/off operation. LSM W3
Series DC/DC converters are designed so that they are enabled when the con-
trol pin is left open (open collector) and disabled when the control pin is pulled
low (to less than +0.4V relative to Common). As shown in Figure 4, all models
have an internal pull-up current source to VIN (+Input).
Dynamic control of the on/off function is best accomplished with a mechanical
relay or open-collector/open-drain drive circuit (optically isolated if appropri-
ate). The drive circuit should be able to sink appropriate current when activated
and withstand appropriate voltage when deactivated.
Applying an external voltage to the On/Off Control pin when no input power is
applied to the converter can cause permanent damage to the converter. The
on/off control function, however, is designed such that the converter can be
disabled (control pin pulled low) while input voltage is ramping up and then
“released” once the input has stabilized (see also power-up sequencing).
Power-up Sequencing
If a controlled start-up of one or more LSM W3 Series DC/DC converters
is required, or if several output voltages need to be powered-up in a given
sequence, the On/Off control pin can be driven with an external open collector
device as per Figure 4.
Leaving the input of the on/off circuit closed during power-up will have the
output of the DC/DC converter disabled. When the input to the external open
collector is pulled high, the DC/DC converter’s output will be enabled.
Output Overvoltage Protection
LSM W3 SMT Series DC/DC converters do not incorporate output overvoltage
protection. In the extremely rare situation in which the device’s feedback loop
is broken, the output voltage may run to excessively high levels (VOUT = VIN). If it
is absolutely imperative that you protect your load against any and all possible
overvoltage situations, voltage limiting circuitry must be provided external to
the power converter.
Figure 5. Inverting On/Off Control With An External CMOS Gate
Figure 4. On/Off Control Using An External Open Collector Driver
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LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 5 of 12
www.murata-ps.com/support
“T” Model (LSM-T/16-W3)
This version of the LSM-W3 series offers a special output voltage trimming
feature which is fully compatible with competitive units. The output voltage
may be varied using a single trim resistor from the Trim input (pin 5) to Power
Common (pin 3). The output voltage range is 0.75 Volts to 3.3 Volts.
IMPORTANT: For outputs greater than 3 Volts up to 3.3 Volts maximum, the
input supply must be 4.5 Volts minimum.
As with other trim adjustments, be sure to use a precision low-tempco resistor
(±100 ppm/°C) mounted close to the converter with short leads. Also be aware
that the output voltage accuracy is ±2% (typical) therefore you may need to
vary this resistance slightly to achieve your desired output setting.
The trim equation is as follows for the LSM-T/16-W3:
LSM-T/16-W3 fi xed resistance values to set the output voltages are:
VOUT (Typ.) 0.75V 1.0V 1.2V 1.5V 1.8V 2.5V 3.3V
RTRIM (kΩ)Open 80.021 41.973 23.077 15.004 6.947 3.16
CAUTION: To retain proper regulation, do not exceed the 3.3V output.
Voltage Trim
The LSM-T/16-W3 may also be trimmed using an external voltage applied
between the Trim input and Output Common. Be aware that the internal “load”
impedance looking into the Trim pin is approximately 5kΩ. Therefore, you may
have to compensate for this in the source resistance of your external voltage
reference.
The equation for this voltage adjustment is:
V
TRIM (in Volts) = 0.7 –(0.1698 x (VO – 0.7525))
The LSM-T/16-W3 fi xed trim voltages to set the output voltage are:
VOUT (Typ.) 0.75V 1.0V 1.2V 1.5V 1.8V 2.5V 3.3V
VTRIM Open 0.6928V 0.624V 0.5731V 0.5221V 0.4033V 0.267V
Figure 6. Trim Connections Using a Trimpot
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Note: Resistor values are in kΩ. Accuracy of adjustment is subject to toler-
ances of resistors and factory-adjusted, initial output accuracy. VO = desired
output voltage. VONOM = nominal output voltage.
Figure 7. Trim Connections Using Fixed Resistors
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trim-up resistor or a fi xed
trim-down resistor depending
upon desired output voltage.
Trim Equations
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21070
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 6 of 12
www.murata-ps.com/support
Output Reverse Conduction
Many DC/DC’s using synchronous rectifi cation suffer from Output Reverse
Conduction. If those devices have a voltage applied across their output before
a voltage is applied to their input (this typically occurs when another power
supply starts before them in a power-sequenced application), they will either
fail to start or self destruct. In both cases, the cause is the “freewheeling” or
“catch” FET biasing itself on and effectively becoming a short circuit.
LSM W3 SMT DC/DC converters do not suffer from Output Reverse Conduc-
tion. They employ proprietary gate drive circuitry that makes them immune to
moderate applied output overvoltages.
Thermal Considerations and Thermal Protection
The typical output-current thermal-derating curves shown below enable
designers to determine how much current they can reliably derive from each
model of the LSM W3 SMT’s under known ambient-temperature and air-fl ow
conditions. Similarly, the curves indicate how much air fl ow is required to reli-
ably deliver a specifi c output current at known temperatures.
The highest temperatures in LSM W3 SMT’s occur at their output inductor,
whose heat is generated primarily by I2R losses. The derating curves were
developed using thermocouples to monitor the inductor temperature and vary-
ing the load to keep that temperature below +110°C under the assorted condi-
tions of air fl ow and air temperature. Once the temperature exceeds +115°C
(approx.), the thermal protection will disable the converter. Automatic restart
occurs after the temperature has dropped below +110°C.
As you may deduce from the derating curves and observe in the effi ciency
curves on the following pages, LSM W3 SMT’s maintain virtually constant
effi ciency from half to full load, and consequently deliver very impressive
temperature performance even if operating at full load.
Lastly, when LSM W3 SMT’s are installed in system boards, they are obviously
subject to numerous factors and tolerances not taken into account here. If you
are attempting to extract the most current out of these units under demanding
temperature conditions, we advise you to monitor the output-inductor tempera-
ture to ensure it remains below +110°C at all times.
Start Up Considerations
When power is fi rst applied to the DC/DC converter, operation is different than
when the converter is running and stabilized. There is some risk of start up
diffi culties if you do not observe several application features. Lower input volt-
age converters may have more problems here since they tend to have higher
input currents. Operation is most critical with any combination of the following
external factors:
1 – Low initial input line voltage and/or poor regulation of the input source.
2 – Full output load current on lower output voltage converters.
3 – Slow slew rate of input voltage.
4 – Longer distance to input voltage source and/or higher external input
source impedance.
5 – Limited or insuffi cient ground plane. External wiring that is too small.
6 – Too small external input capacitance. Too high ESR.
7 – High output capacitance causing a start up charge overcurrent surge.
8 – Output loads with excessive inductive reactance or constant current
characteristics.
If the input voltage is already at the low limit before power is applied, the start
up surge current may instantaneously reduce the voltage at the input terminals
to below the specifi ed minimum voltage. Even if this voltage depression is very
brief, this may interfere with the on-board controller and possibly cause a failed
start. Or the converter may start but the input current load will now drive the
input voltage below its running low limit and the converter will shut down.
If you measure the input voltage before start up with a Digital Voltmeter (DVM),
the voltage may appear to be adequate. Limited external capacitance and/or
too high a source impedance may cause a short downward spike at power up,
causing an instantaneous voltage drop. Use an oscilloscope not a DVM to observe
this spike. The converter’s soft-start controller is sensitive to input voltage. What
matters here is the actual voltage at the input terminals at all times.
Symptoms of start-up diffi culties may include failed started, output oscillation or
brief start up then overcurrent shutdown. Since the input voltage is never abso-
lutely constant, the converter may start up at some times and not at others.
Solutions
To improve start up, review the conditions above. One of the better solutions is
to place a moderate size capacitor very close to the input terminals. You may
need two parallel capacitors. A larger electrolytic or tantalum cap supplies the
surge current and a smaller parallel low-ESR ceramic cap gives low AC imped-
ance. Too large an electrolytic capacitor may have higher internal impedance
(ESR) and/or lower the start up slew rate enough to upset the DC/DC’s control-
ler. Make sure the capacitors can tolerate refl ected switching current pulses
from the converter.
The capacitors will not help if the input source has poor regulation. A converter
which starts successfully at 3.3 Volts will turn off if the input voltage decays to
below the input voltage theshold, regardless of external capacitance.
Increase the input start up voltage if possible to raise the downward voltage
spike. Also, make sure that the input voltage ramps up in a reasonably short
time (less than a few milliseconds). If possible, move the input source closer to
the converter to reduce ohmic losses in the input wiring. Remember that the
input current is carried both by the wiring and the ground plane return. Make
sure the ground plane uses adequate thickness copper. Run additional bus wire
if necessary.
Any added output capacitor should use just enough capacitance (and no
more) to reduce output noise at the load and to avoid marginal threshold noise
problems with external logic. An output cap will also “decouple” inductive reac-
tance in the load. Certain kinds of electronic loads include “constant current”
characteristics which destabilize the output with insuffi cient capacitance. If the
wiring to the eventual load is long, consider placing this decoupling cap at the
load. Use the Remote Sense input to avoid ohmic voltage drop errors.
An elegant solution to start up problems is to apply the input voltage with
the Remote On/Off control fi rst in the off setting (for those converters with an
On/Off Control). After the specifi ed start-up delay (usually under 20 mSec), turn
on the converter. The controller will have already been stabilized. The short
delay will not be noticed in most applications. Be aware of applications which
need “power management” (phased start up).
Finally, it is challenging to model some application circuits with absolute fi delity.
How low is the resistance of your ground plane? What is the inductance (and
distributed capacitance) of external wiring? Even a detailed mathematical
model may not get all aspects of your circuit. Therefore it is diffi cult to give cap
values which serve all applications. Some experimentation may be required.
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 7 of 12
www.murata-ps.com/support
Typical Performance Curves for the LSM W3 SMT Series
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LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 8 of 12
www.murata-ps.com/support
Typical Performance Curves for the LSM W3 SMT Series
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LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 9 of 12
www.murata-ps.com/support
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LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 10 of 12
www.murata-ps.com/support
Tape & Reel Surface Mount Package
DATEL’s LSM series DC/DC converters are the only higher-current (16A) SMT
DC/DC’s that can be automatically “pick-and-placed” using standard vacuum-
pickup equipment (nozzle size and style, vacuum pressure and placement
speed may need to be optimized for automated pick and place) and subse-
quently refl owed using high-temperature, lead-free solder.
Virtually all SMT DC/DC’s today are unprotected “open-frame” devices assem-
bled by their vendors with high-temperature solder (usually Sn96.5/Ag3.5
with a melting point +221°C) so that you may attach them to your board using
low-temperature solder (usually Sn63/Pb37 with a melting point of +183°C).
Conceptually straightforward, this “stepped” solder approach has its limita-
tions, and it is clearly out of step with an industry trending toward the broad
use of lead-free solders. Are you to experiment and develop refl ow profi les
from other vendors that ensure the components on those DC/DC never exceed
215-216°C? If those components get too hot, “double-refl ow” could compro-
mise the reliability of their solder joints. Virtually all these devices demand you
“cool down” the Sn63 profi le you are likely using today.
Figure 6. Refl ow Solder Profi le
DATEL is not exempted from the Laws of Physics, and we do not have
magic solders no one else has. Nevertheless, we have a simple and
practical, straightforward approach that works. We assemble our LSM SMT
DC/DC’s using a high-temperature (+216°C), lead-free alloy (Sn96.2%,
Ag2.5%, Cu0.8%, Sb0.5%). The LSM design ensures co-planarity to
within 0.004 inches (100μ1m) of the unit’s copper leads. These units are
gold-plated with a nickel underplate. See Mechanical Data for additional
information.
The disposable heat shield (patent pending), which has a cutaway exposing
the package leads, provides thermal insulation to internal components
during refl ow and its smooth surface ideally doubles as the vacuum pick-up
location also. The insulation properties of the heat shield are so effective
that temperature differentials as high as 50°C develop inside-to-outside the
shield. Oven temperature profi les with peaks of 250-260°C and dwell times
exceeding 2 minutes above 221°C (the melting point of Sn96.5/Ag3.5) are
easily achieved.
HEAT SHIELD OUTSIDE TEMPERATURE
Sn96.5/Ag3.5 Melting Point
Sn63/Pb37 Melting Point
250
200
150
100
50
0 50 100 150 200 250 300 350 400
221
183
PCB TEMPERATURE INSIDE THE HEAT SHIELD
Temperature (˚C)
Time
(
Seconds
)
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 11 of 12
www.murata-ps.com/support
0.51(13.0)
7.38 (187.5)
13.0 (330.2)
2.44
(62.0)
DATEL’s new-generation LSM SMT DC/DC converters are shipped in quantities of 150 modules per tape and reel.
Figure 7. Tape Dimensions
Figure 8. Reel Dimensions
CAUTION
PRESS TO REMOVE
THE HEAT SHIELD
AFTER THE SOLDER
PROCESS.
NOTCH IN SHELL
INDICATES
PIN ONE.
0.158
(4) CENTERED
PICK UP
LOCATION
2.205
(56)
2.063
(52.4)
FEED
DIRECTION
1.370
(34.8)
1.102
(28)
0.605
(15.36)
TA P E
0.590
(14.97)
DIMENSIONS
IN INCHES (mm)
111
LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
MDC_LSM-16A_W3.B01 Page 12 of 12
Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifi cations are subject to change without
notice. © 2012 Murata Power Solutions, Inc.
www.murata-ps.com/support
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
