www.murata-ps.com/support
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
MDC_LSM2 Series.D01∆ Page 4 of 17
Performance/Functional Specification Notes:
(1) All models are tested and specified with external 1 || 10µF ceramic/tantalum output
capacitors and a 22µF external input capacitor. All capacitors are low ESR types. These
capacitors are necessary to accommodate our test equipment and may not be required
to achieve specified performance in your applications. All models are stable and
regulate within spec under no-load conditions.
General conditions for Specifications are +25°C, Vin = nominal, Vout = nominal, full
load. “Nominal” output voltage is +5V for D12 models and +3.3V for W3 models.
(2) Input Back Ripple Current is tested and specified over a 5-20MHz bandwidth. Input
filtering is Cin = 2 × 100µF tantalum, Cbus = 1000µF electrolytic, Lbus = 1µH.
(3) Note that Maximum Power Derating curves indicate an average current at nominal
input voltage. At higher temperatures and/or lower airflow, the DC/DC converter will
tolerate brief full current outputs if the total RMS current over time does not exceed the
derating curve.
(4) Mean Time Before Failure is calculated using the Telcordia (Belcore) SR-332 Method 1,
Case 3, ground fixed conditions, Tpcboard = +25°C, full output load, natural air convec-
tion.
(5) The On/Off Control may be driven with external logic or by applying appropriate exter-
nal voltages which are referenced to –Input Common. The On/Off Control Input should
use either an open collector/open drain transistor or logic gate which does not exceed
+Vin. A 68KΩ external pullup resistor to +Vin will cause the “ON” state for negative
logic models.
(6) Short circuit shutdown begins when the output voltage degrades approximately 2%
from the selected setting.
I/O Filtering and Noise Reduction
All models in the LSM2 Series are tested and specified with external 1 || 10µF
ceramic/tantalum output capacitors and a 22µF tantalum input capacitor. These
capacitors are necessary to accommodate our test equipment and may not be
required to achieve desired performance in your application. The LSM2s are
designed with high-quality, high-performance internal I/O caps, and will oper-
ate within spec in most applications with no additional external components.
In particular, the LSM2’s input capacitors are specified for low ESR and
are fully rated to handle the units' input ripple currents. Similarly, the internal
output capacitors are specified for low ESR and full-range frequency response.
In critical applications, input/output ripple/noise may be further reduced using
filtering 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/DCs requires that the dc input voltage source have low ac
impedance at the frequencies of interest. Highly inductive source impedances
can greatly affect system stability. Your specific system configuration may
necessitate additional considerations.
Output ripple/noise (also referred to as periodic and random deviations or
PARD) may be reduced below specified limits with the installation of additional
external output capacitors. Output capacitors function as true filter elements
and should be selected for bulk capacitance, low ESR, and appropriate fre-
quency response. Any scope measurements of PARD should be made directly
TECHNICAL NOTES
(7) If Sense is connected remotely at the load, up to 0.5 Volts difference is allowed
between the Sense and +Vout pins to compensate for ohmic voltage drop in the power
lines. A larger voltage drop may cause the converter to exceed maximum power dis-
sipation. Connect sense to +Vout if not used.
(8) Output noise may be further reduced by adding an external filter. See I/O Filtering and
Noise Reduction.
(9) All models are fully operational and meet published specifications, including “cold
start” at –40°C.
(10) Regulation specifications describe the deviation as the line input voltage or output load
current is varied from a nominal midpoint value to either extreme.
(11) Other input or output voltage ranges are available under scheduled quantity special order.
(12) Maximum PC board temperature is measured with the sensor in the center.
(13) Do not exceed maximum power specifications when adjusting the output trim.
(14) The maximum output capacitive loads depend on the the Equivalent Series Resistance
(ESR) of the external output capacitor.
(15) Do not use Pre-bias startup and sequencing together. See Technical Notes below.
(16) After short circuit shutdown, if the load is partially removed such that the load still ex-
ceeds the overcurrent (OC) detection, the converter will remain in hiccup restart mode.
(17) When Sequencing is not used, the Power Good output is TRUE at any time the output
is within approximately ±10% of the voltage set point. Power Good basically indicates
if the converter is in regulation. Power Good detects Over Temperature if the PWM has
shut down due to OT. Power Good does not directly detect Over Current.
If Sequencing is in progress, Power Good will falsely indicate TRUE (valid) before the
output reaches its setpoint. Ignore Power Good if Sequencing is in transition.
at the DC/DC output pins with scope probe ground less than 0.5" in length.
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.
Input Fusing
Most applications and or safety agencies require the installation of fuses at the
inputs of power conversion components. The LSM2 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.
Safety Considerations
LSM2 SMTs are non-isolated DC/DC converters. In general, all DC/DCs must
be installed, including considerations for I/O voltages and spacing/separation
requirements, in compliance with relevant safety-agency specifications (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
LSM2 SMT Series DC/DCs do not incorporate either input overvoltage or input
reverse-polarity protection. Input voltages in excess of the specified absolute
maximum ratings and input polarity reversals of longer than "instantaneous"
duration can cause permanent damage to these devices.
