LSM2 Series
www.murata-ps.com
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Typical Unit
Murata Power Solutions’ miniature POL switching DC/DC
converters are ideal regulation and supply elements for
mixed voltage systems.
FEATURES
PRODUCT OVERVIEW
Point-of-load (POL) converters for
mixed voltage systems
5V & 12V wide input ranges
They are fully compatible with the Distributedpower Open Standards Alliance specification
(www.dosapower.com). LSM2s can power CPU’s,
programmable logic and mixed voltage systems
with little heat and low noise. A typical application uses a master isolated 12 or 5 Volt DC supply
and individual LSM2 converters for local 1.8 and
3.3 Volt DC supplies. All system isolation resides
6, 10 or 16 Amp maximum outputs
DOSA compatible SMT package
Meets RoHS-6 compliance
Phased start up sequencing and tracking
in the central supply, leaving lower cost POL
regulation right at the load. Unlike linear regulators, the LSM2’s can deliver very high power (up to
52 Watts) in a tiny area with no heat sinking and no
external components needed. They feature quick
transient response (to 25µsec) and very fast current
slew rates (to 20A/µsec).
Extensive self-protection
Starts up into pre-biased loads
CONNECTION DIAGRAM
+OUTPUT
+INPUT
+SENSE
COMMON
COMMON
VCC
ON/OFF
CONTROL
VTRACK/
SEQUENCE
INPUT
PWM
CONTROLLER
CURRENT
SENSE
POWER
GOOD
REFERENCE &
ERROR AMP
VOUT
TRIM
Typical topology is shown
For full details go to
www.murata-ps.com/rohs
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MDC_LSM2 Series.D02∆ Page 1 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
PERFORMANCE SPECIFICATIONS AND ORDERING GUIDE
Output
Input
R/N (mVp-p)
Regulation
Line
Load
Root Model
VOUT
(Volts)
IOUT
(Amps)
Power
(Watts)
Typ.
Max.
LSM2-T/6-W3-C
0.75-3.3
6
19.8
20
40
±0.11%
±0.075%
5
2.4-5.5
LSM2-T/6-D12-C
0.75-5
6
30.0
30
90
±0.075%
±0.15%
12
8.3-13.2
LSM2-T/10-W3-C
0.75-3.3
10
33.0
58
79
±0.15%
±0.075%
5
2.4-5.5
LSM2-T/10-D12-C
0.75-5
10
50.0
62
80
±0.07%
±0.15%
12
LSM2-T/16-W3-C
0.75-3.3
16
52.8
83
110
±0.1%
±0.075%
5
16
80.0
90
125
±0.1%
±0.21%
12
LSM2-T/16-D12-C 0.75-5
Typical at TA = +25°C under nominal line voltage and full-load conditions, unless noted.
Ripple/Noise (R/N) is tested/specified over a 20MHz bandwidth and may be reduced
with external filtering. See I/O Filtering and Noise Reduction for details.
These devices have no minimum-load requirements and will regulate under no-load
conditions. Regulation specifications describe the output-voltage deviation as the line
voltage or load is varied from its nominal/midpoint value to either extreme.
Efficiency
Min.
Typ.
Package
(Case/Pinout)
50/4.15
93%
95.5%
C63, P67
70/2.68
91.9%
93.4%
C63, P67
75/6.91
94%
95.5%
C62, P66
8.3-13.2 100/4.368 93.5%
95.4%
C62, P66
2.4-5.5
70/11.15
92.8%
94.7%
C62, P66
8.3-13.2
100/7.1
93%
94%
C62, P66
VIN Nom. Range
IIN
(Volts) (Volts) (mA/A)
Nominal line voltage, no-load/full-load conditions.
LSM2-T16-D12 efficiencies are shown at 5VOUT.
VIN must be ≥0.5V greater than VOUT.
These are not complete model numbers. Please refer to the Part Number Structure
when ordering.
➇ RoHS-6 compliance does not claim EU RoHS exemption 7b (lead in solder).
PART NUMBER STRUCTURE
L SM2 - T / 16 - D12 N G - C
Output Configuration:
L = Unipolar
Low Voltage
Non-Isolated SMT
Nominal Output Voltage:
0.75-3.3 Volts (W3)
0.75-5 Volts (D12)
Maximum Rated Output
Current in Amps
RoHS6 compliant*
(see note 8)
Power Good Output: **
Blank = Omitted
G = Installed
On/Off Polarity:
Blank = Positive polarity
N = Negative polarity
Input Voltage Range:
D12 = 8.3-14 Volts (12V nominal)
W3 = 2.4-5.5 Volts (5V nominal)
Note:
Not all model number combinations
are available. Contact MPS.
* Contact MPS (DATEL) for availability.
** The Power Good option is not available for
LSM2-T/10-D12 and LSM2-T/16-D12. Models
without Power Good do not install pad 8 (10/16
Amp). For 6 Amp models, pad 7 is only installed
for “G” models.
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MDC_LSM2 Series.D02∆ Page 2 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Performance/Functional Specifications (1)
INPUT
Input Voltage Range
See Ordering Guide
Isolation
Not isolated, input and output use the same
common return.
Start-Up Threshold
W3 Models
12V Models
2.2 Volts
8 Volts
Undervoltage Shutdown
W3 Models
12V Models
2.0 Volts
7.5 Volts
Pre-bias Startup (15)
Converter will start up if the external
output voltage is less than VNOM
Sequencing
Slew Rate
Startup delay until sequence start
Tracking accuracy, rising input
Tracking accuracy, falling input
Sequence pin input impedance
2V max. per millisecond
10 milliseconds
VOUT = ±100mV of Sequence In
VOUT = ±200mV of Sequence In
400kW to 1MW
Remote Sense to VOUT
0.5V max. (7)
Power Good Output (17)
(“G” suffix)
Power_Good Configuration
TRUE (OK) = open drain
FALSE (not OK) = Signal Ground to 0.4V
MOSFET to ground with external user
pullup, 10mA max. sink
Overvoltage Shutdown
None
Reflected (Back) Ripple Current (2)
20-70mAp-p (model dependent)
Internal Input Filter Type
Capacitive
Reverse Polarity Protection
See fuse information
Dynamic Load Response
25µsec to ±2% of final value
(50-100-50% load step, di/dt = 20A/µsec)
See Ordering Guide
0.1-0.4A2sec (model dependent)
5mA
60mA
Start-Up Time
7msec for VOUT = nominal
(VIN on to VOUT regulated or On/Off to VOUT)
Input Current:
Full Load Conditions
Inrush Transient
Shutdown Mode (Off, UV, OT)
Output Short Circuit
Low Line (VIN = VMIN)
LSM2-T/6-W3
LSM2-T/6-D12
LSM2-T/10-W3
LSM2-T/10-D12
LSM2-T/16-W3
LSM2-T/16-D12
5.54 Amps
3.79 Amps
9.14 Amps
6.375 Amps
14.63 Amps
10.2 Amps
Remote On/Off Control: (5)
Positive Logic (no model suffix)
OFF = ground pin to +0.3V max.
ON = open pin or +VIN max.
ON = Open pin or 0 to +0.3V max.
OFF = +2.5V to +VIN max.
1mA max.
Negative Logic (“N” model suffix)
Current
OUTPUT
DYNAMIC CHARACTERISTICS
Switching Frequency
LSM2-T/6 models
LSM2-T/10 and -T/16 models
315kHz
230kHz
ENVIRONMENTAL
Calculated MTBF (4)
TBC Hours
Operating Temperature Range (Ambient) –40 to +85°C with derating (9)
See Derating Curves
Operating PC Board TemUperature
–40 to +100°C max. (12)
Storage Temperature Range
–55 to +125°C
Thermal Protection/Shutdown
+115°C
Relative Humidity
to 85% / +85°C, non-condensing
PHYSICAL
Outline Dimensions
See Mechanical Specifications
Voltage Output Range
See Ordering Guide
Removable Heat Shield
Nylon 46
Minimum Loading
No minimum load
Weight
0.28 ounces (7.8 grams)
Accuracy (50% load)
±2% of VNOM
Lead Material
Tin-plated copper alloy
Voltage Adjustment Range (13)
See Ordering Guide
Designed to meet FCC part 15, class B,
Temperature Coefficient
±0.02% of VOUT range per °C
Ripple/Noise (20 MHz bandwidth)
See Ordering Guide and (8)
Electromagnetic Interference
EN55022
(conducted and radiated)
Safety
C22.2
60950-1
Designed to meet UL/cUL 60950-1 CSANo.234 IEC/EN
Flammability
UL94V-0
Line/Load Regulation (See Tech Notes) See Ordering Guide and (10)
Efficiency
Maximum Capacitive Loading: (14)
LSM2-T/6 models:
Cap-ESR = 0.001 to 0.01W
Cap-ESR >0.01W
LSM2-T/10 and -T/16 models:
Cap-ESR = 0.001 to 0.01W
Cap-ESR >0.01W
Current Limit Inception: (98% of VOUT)
LSM2-T/6 models
LSM2-T/10 models
LSM2-T/16 models
Short Circuit Mode (6)
Short Circuit Current Output
Protection Method (16)
Short Circuit Duration
ground)
See Ordering Guide
3000µF
5000µF
5000µF
10,000µF
10 Amps (after warm up)
16.75 Amps (after warm startup)
21–31 Amps (after warm up)
600mA
Hiccup autorecovery on overload removal
Continuous, no damage (output shorted to
(may need external filter)
ABSOLUTE MAXIMUM RATINGS
Input Voltage (Continuous or transient)
W3 models
12V models
+7 Volts
+15 Volts
On/Off Control
–0.3V min. to +VIN max.
Input Reverse Polarity Protection
See Fuse section
Output Current (7)
Current-limited. Devices can
withstand sustained short circuit
without damage.
Storage Temperature
–55 to +125°C
Lead Temperature (soldering 10 sec. max.) +280°C
These are stress ratings. Exposure of devices to greater than any of these conditions may
adversely affect long-term reliability. Proper operation under conditions other than those listed in
the Performance/Functional Specifications Table is not implied.
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MDC_LSM2 Series.D02∆ Page 3 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Performance/Functional Specification Notes:
(1)
(2)
(3)
(4)
(5)
(6)
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.
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.
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.
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 convection.
The On/Off Control may be driven with external logic or by applying appropriate external 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.
Short circuit shutdown begins when the output voltage degrades approximately 2%
from the selected setting.
TECHNICAL NOTES
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 operate 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 appropriate 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 frequency response. Any scope measurements of PARD should be made directly
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
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 dissipation. Connect sense to +Vout if not used.
Output noise may be further reduced by adding an external filter. See I/O Filtering and
Noise Reduction.
All models are fully operational and meet published specifications, including “cold
start” at –40°C.
Regulation specifications describe the deviation as the line input voltage or output load
current is varied from a nominal midpoint value to either extreme.
Other input or output voltage ranges are available under scheduled quantity special order.
Maximum PC board temperature is measured with the sensor in the center.
Do not exceed maximum power specifications when adjusting the output trim.
The maximum output capacitive loads depend on the the Equivalent Series Resistance
(ESR) of the external output capacitor.
Do not use Pre-bias startup and sequencing together. See Technical Notes below.
After short circuit shutdown, if the load is partially removed such that the load still exceeds the overcurrent (OC) detection, the converter will remain in hiccup restart mode.
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.
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MDC_LSM2 Series.D02∆ Page 4 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
TO
OSCILLOSCOPE
CURRENT
PROBE
+INPUT
LBUS
+
VIN
2
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.
CBUS
CIN
–
3
COMMON
CIN = 2 x 100µF, ESR < 700mΩ @ 100kHz
CBUS = 1000µF, ESR < 100mΩ @ 100kHz
LBUS = 1µH
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
Figure 2. Measuring Input Ripple Current
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 specified input voltage range
and the fully loaded output voltage enters and remains within its specified
accuracy band. Actual measured times will vary with input source impedance,
external input capacitance, and the slew rate and final value of the input voltage as it appears to the converter.
+SENSE
+OUTPUT
6
COPPER STRIP
COMMON
C2
(VOUT at pins) x (IOUT) ≤ rated output power
The internal 10.5Ω resistor between +Sense and +Output (see Figure 1)
serves to protect the sense function by limiting the output current flowing
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 must
be tied to +Output at the DC/DC converter pins.
4
C1
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 LSM2's specified rating. Therefore:
SCOPE
RLOAD
3
COPPER STRIP
C1 = NA
C2 = 22µF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3. Measuring Output Ripple/Noise (PARD)
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 specification defines the interval between the time at which the converter
is turned on and the fully loaded output voltage enters and remains within its
specified accuracy band. See Typical Performance Curves.
Remote Sense
LSM2 Series offer an output sense function. The sense function enables
point-of-use regulation for overcoming moderate 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.
Sense Input
Use the Sense input with caution. Many applications do not need the Sense
connection. Sense is intended to correct small output accuracy errors caused
by the resistive ohmic drop in output wiring as output current increases. This
output drop (the difference between Sense and VOUT when measured at the
converter) should not be allowed to exceed 0.5V. Consider using heavier wire if
this drop is excessive.
Sense is connected at the load and corrects for resistive errors only. Be
careful where it is connected. Any long, distributed wiring and/or significant
inductance introduced into the Sense control loop can adversely affect overall
system stability. If in doubt, test the application, and observe the DC/DC's output
transient response during step loads. There should be no appreciable ringing or
oscillation. You may also adjust the output trim slightly to compensate for voltage
loss in any external filter elements. Do not exceed maximum power ratings.
On/Off Control
The On/Off Control pin may be used for remote on/off operation. LSM2 Series
DC/DC converters are designed so that they are enabled when the control pin
is left open (open collector).
Dynamic control of the on/off function is best accomplished with a mechanical relay or open-collector/open-drain drive circuit (optically isolated if
appropriate). The drive circuit should be able to sink appropriate current when
activated and withstand appropriate voltage when deactivated.
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MDC_LSM2 Series.D02∆ Page 5 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
+INPUT
+V
SMALL
SIGNAL
TRANSISTOR
HI = OFF
LO = ON
ON/OFF
CONTROL
SIGNAL
GROUND
SHUTDOWN
CONTROLLER
COMMON
Figure 4. On/Off Control Using An External Open Collector Driver
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 LSM2 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
LSM2 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.
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. LSM2 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% or if the
output voltage drops to less than 98% of it original value, the LSM2'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. Once the
output short is removed, the converter will automatically restart itself.
Output Reverse Conduction
Many DC/DCs using synchronous rectification 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.
LSM2 SMT DC/DC converters do not suffer from Output Reverse Conduction. 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 LSM2 SMT's under known ambient-temperature and air-flow
conditions. Similarly, the curves indicate how much air flow is required to reliably deliver a specific output current at known temperatures.
+INPUT
10kΩ
+V
EXTERNAL
OPEN
COLLECTOR
INPUT
ON/OFF
CONTROL
SHUTDOWN
SIGNAL
GROUND
CONTROLLER
COMMON
Figure 5. Inverting On/Off Control
The highest temperatures in LSM2 SMT's occur at their output inductor,
whose heat is generated primarily by I 2 R losses. The derating curves were developed using thermocouples to monitor the inductor temperature and varying
the load to keep that temperature below +110°C under the assorted conditions of air flow 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 efficiency
curves on the following pages, LSM2 SMT's maintain virtually constant
efficiency from half to full load, and consequently deliver very impressive
temperature performance even if operating at full load.
Lastly, when LSM2 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 temperature to ensure it remains below +110°C at all times.
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MDC_LSM2 Series.D02∆ Page 6 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Start Up Considerations
When power is first applied to the DC/DC converter, operation is different than
when the converter is running and stabilized. There is some risk of start up
difficulties if you do not observe several application features. Lower output
voltage converters may have more problems here since they tend to have
higher output currents. Operation is most critical with any combination of the
following external factors:
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.
1 – Low initial input line voltage and/or poor regulation of the input source.
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 reactance in the load. Certain kinds of electronic loads include “constant current”
characteristics which destabilize the output with insufficient 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.
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 insufficient 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 specified 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 difficulties may include failed started, output oscillation or brief start up then overcurrent shutdown. Since the input voltage is never
absolutely 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 impedance. 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 controller. Make sure the capacitors can tolerate reflected 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.
An elegant solution to start up problems is to apply the input voltage with
the Remote On/Off control first in the off setting (for those converters with an
On/Off Control). After the specified 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 fidelity. 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 difficult to give cap values
which serve all applications. Some experimentation may be required.
Pre-Biased Startup
Newer systems with multiple power voltages have an additional problem
besides startup sequencing. Some sections have power already partially applied (possibly because of earlier power sequencing) or have leakage power
present so that the DC/DC converter must power up into an existing voltage.
This power may either be stored in an external bypass capacitor or supplied by
an active source.
This “pre-biased” condition can also occur with some types of programmable logic or because of blocking diode leakage or small currents passed
through forward biased ESD diodes. Conventional DC/DCs may fail to start up
correctly if there is output voltage already present. And some external circuits
are adversely affected when the low side MOSFET in a synchronous rectifier
converter sinks current at start up.
The LSM2 series includes a pre-bias startup mode to prevent these initialization problems. Essentially, the converter acts as a simple buck converter until the
output reaches its set point voltage at which time it converts to a synchronous
rectifier design. This feature is variously called “monotonic” because the voltage
does not decay (from low side MOSFET shorting) or produce a negative transient
once the input power is applied and the startup sequence begins.
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MDC_LSM2 Series.D02∆ Page 7 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Don’t Use Pre-Biasing and Sequencing Together
Normally, you would use startup sequencing on multiple DC/DC’s to solve the
Pre-Bias problem. By causing all power sources to ramp up together, no one
source can dominate and force the others to fail to start. For most applications, do not use startup sequencing in a Pre-Bias application, especially with
an external active power source. If you have active source pre-biasing, leave
the Sequence input open so that the output will step up quickly and safely. A
symptom of this condition is repeated failed starts. You can further verify this
by removing the existing load and testing it with a separate passive resistive
load which does not exceed full current. If the resistive load starts successfully,
you may be trying to drive an external pre-biased active source.
It may also be possible to use pre-bias and sequencing together if the PreBias source is in fact only a small external bypass capacitor slowly charged by
leakage currents. Test your application to be sure.
Output Adjustments
The LSM2 series includes 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 to Power Common (pin 4) or an
external DC trim voltage applied between the Trim input and Power Common.
The output voltage range for W3 models is 0.75 to 3.3 Volts. For D12 models,
the output range is 0.75 to 5 Volts.
IMPORTANT: On W3 models only, for outputs greater than 3 Volts up to
3.3 Volts maximum, the input supply must be 4.5 Volts minimum. To retain
proper regulation, do not exceed the 3.3V output.
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.
D12 Models Resistor Trim Equation:
10500
RTRIM (W) = _____________ –1000
VO – 0.7525
Vout (Typ.)
0.7525V
1.0V
1.2V
1.5V
1.8V
2.5V
3.3V
Rtrim (kW)
Open
41.424
22.46
13.05
9.024
5.009
3.122 1.472
5V
Voltage Trim
The LSM2 Series 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 trim pin is approximately 5 Kilohms. Therefore, you
may have to compensate for this in the source resistance of your external voltage reference.
Use a low noise DC reference and short leads. Mount the leads close to the
converter.
Two different trim equations are used for the W3 and D12 models.
W3 Models Voltage Trim Equation:
VTRIM (in Volts) = 0.7 – (0.1698 x (VO – 0.7525))
The LSM2 W3 fixed trim voltages to set the output voltage are:
Vout (Typ.)
0.7525V
1.0V
1.2V
Vtrim
Open
0.6928V
0.624V
1.5V
1.8V
2.5V
0.5731V 0.5221V 0.4033V
3.3V
0.267V
D12 Models Voltage Trim Equation:
VTRIM (in Volts) = 0.7 – (0.0667 x (VO – 0.7525))
Two different trim equations are used for the W3 and D12 models.
W3 Models Resistor Trim Equation:
The LSM2 D12 fixed trim voltages to set the output voltage are:
21070
RTRIM (W) = _____________ – 5110
VO – 0.7525
Vout (Typ.)
0.7525V
Vtrim
Open
1.0V
1.2V
1.5V
1.8V
2.5V
3.3V
5V
0.6835 0.670
0.650
0.630
0.583
0.530 0.4166
The W3 models fixed trim resistors to set the output voltage are:
Vout (Typ.)
0.7525V
1.0V
1.2V
1.5V
1.8V
2.5V
3.3V
Rtrim (kW)
Open
80.021
41.973
23.077
15.004
6.947
3.16
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MDC_LSM2 Series.D02∆ Page 8 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Typical Performance Curves
LSM2-T/6-D12 Maximum Current Temperature Derating
VOUT = 5V (air flow from input to output)
LSM2-T/6-D12
Efficiency vs. Line Voltage and Load Current @ 25°C (VOUT = 5V)
6.5
95
94
6
Output Current (Amps)
93
Efficiency (%)
92
91
90
89
Natural Convection
5
100 lfm
200 lfm
VIN = 8.3V
88
5.5
4.5
400 lfm
VIN = 12V
87
85
4
–40
VIN = 14V
86
25
30
35
40
45
50
55
60
65
70
75
80
85
80
85
Ambient Temperature (°C)
1
2
3
4
5
6
Load Current (Amps)
LSM2-T/6-D12
Efficiency vs. Line Voltage and Load Current @ 25°C (VOUT = 0.75V)
LSM2-T/6-D12 Maximum Current Temperature Derating
VOUT = 0.75V (air flow from input to output)
84
6.5
82
Output Current (Amps)
6
80
Efficiency (%)
VIN = 8.3V
78
76
74
VIN = 14V
2
3
5
100 lfm
4
–40
70
1
Natural Convection
4.5
VIN = 12V
72
5.5
4
5
6
25
30
35
40
45
50
55
60
65
70
75
Ambient Temperature (°C)
Load Current (Amps)
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MDC_LSM2 Series.D02∆ Page 9 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Tape & Reel Surface Mount Package
MPS’s LSM2 series DC/DC converters are the only higher-current (16A) SMT
DC/DC's that can be automatically “pick-and-placed” using standard vacuumpickup equipment (nozzle size and style, vacuum pressure and placement
speed may need to be optimized for automated pick and place) and subsequently reflowed using high-temperature, lead-free solder.
MPS 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 LSM2 SMT DC/DC's
using a high-temperature (+216°C), lead-free alloy (Sn96.2%, Ag2.5%, Cu0.8%,
Sb0.5%). The LSM2 design ensures co-planarity to within 0.004 inches
(100µ1m) of the unit's tin-plated (150 micro-inches) copper leads. See Mechanical Data for additional information.
Virtually all SMT DC/DCs today are unprotected "open-frame" devices assembled 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 limitations, 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 reflow profiles
from other vendors that ensure the components on those DC/DC never exceed
215-216°C? If those components get too hot, "double-reflow" could compromise the reliability of their solder joints. Virtually all these devices demand you
"cool down" the Sn63 profile you are likely using today.
The disposable heat shield (patent pending), which has a cutaway exposing the package leads, provides thermal insulation to internal components
during reflow 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 profiles 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
250
Sn96.5/Ag3.5 Melting Point
Temperature (˚C)
221
200
183
Sn63/Pb37 Melting Point
150
PCB TEMPERATURE INSIDE THE HEAT SHIELD
100
50
0
50
100
150
200
250
300
350
400
Time (Seconds)
Figure 6. Reflow Solder Profile
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MDC_LSM2 Series.D02∆ Page 10 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
LSM2 TAPE AND REEL SPECIFICATIONS
DATEL's new-generation LSM2 SMT DC/DC converters are shipped in quantities of 150 modules per tape and reel.
1.102
(28)
0.158
(4)
CENTERED
PICK UP
LOCATION
NOTCH IN SHELL
INDICATES
PIN ONE.
1.370
(34.8)
2.205
(56)
2.063
(52.4)
1
1
1
CAUTION
PRESS TO REMOVE
THE HEAT SHIELD
AFTER THE SOLDER
PROCESS.
FEED
DIRECTION
TAPE
DIMENSIONS
IN INCHES (mm)
0.590
(14.97)
Removable Heat Shield
0.605
(15.36)
Figure 7. Tape Dimensions
2.44
(62.0)
13.0 (330.2)
7.38 (187.5)
0.51(13.0)
Figure 8. Reel Dimensions
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MDC_LSM2 Series.D02∆ Page 11 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
LSM2 Power Sequencing
Whereas in the old days, one master switch simultaneously turned on the
power for all parts of a system, many modern systems require multiple supply
voltages for different on-board sections. Typically the CPU or microcontroller
needs 1.8 Volts or lower. Memory (particularly DDR) may use 1.8 to 2.5 Volts.
Interface “glue” and “chipset” logic might use +3.3Vdc power while Input/Output subsystems may need +5V. Finally, peripherals use 5V and/or 12V.
Timing is Everything
This mix of system voltages is being distributed by several local power solutions including Point-of-load (POL) DC/DC converters and sometimes a linear
regulator, all sourced from a master AC power supply. While this mix of voltages is challenging enough, a further difficulty is the start-up and shutdown
timing relationship between these power sources and relative voltage differences between them.
For many systems, the CPU and memory must be powered up, boot-strap
loaded and stabilized before the I/O section is turned on. This avoids uncommanded data bytes being transferred, compromising an active external network
or placing the I/O section in an undefined mode. Or it keeps bad commands out
of disk and peripheral controllers until they are ready to go to work.
Another goal for staggered power-up is to avoid an oversize load applied to
the master source all at once. A more serious reason to manage the timing and
voltage differences is to avoid either a latchup condition in programmable logic
(a latchup might ignore commands or would respond improperly to them) or a
high current startup situation (which may damage on-board circuits). And on
the power down phase, inappropriate timing or voltages can cause interface
logic to send a wrong “epitaph” command.
Two Approaches
There are two ways to manage these timing and voltage differences. Either the
power up/down sequence can be controlled by discrete On/Off logic controls
for each power supply (see Figure 9). Or the power up/down cycle is set by
Sequencing or Tracking circuits. Some systems combine both methods.
The first system (discrete On/Off controls) applies signals from an alreadypowered logic sequencer or dedicated microcontroller which turns on each
downstream power section in cascaded series. This of course assumes all
POL’s have On/Off controls. A distinct advantage of the sequencing controller
is that it can produce an “All On” output signal to state that the full system is
stable and ready to go to work. For additional safety, the sequencer can monitor the output voltages of all downstream POL’s with an A/D converter system.
However the sequencer controller has some obvious difficulties besides
extra cost, wiring and programming complexity. First, power is applied as a
fast-rising, all-or-nothing step which may be unacceptable to certain circuits,
especially large output bypass capacitors. These could force POL’s into overcurrent shutdown. And some circuits (such as many linear regulators and some
POL’s) may not have convenient start-up controls. This requires designing and
fabricating external power controls such as high-current MOSFET’s.
+12Vdc
“ALL ON”
+VIN
POL
A
+5V
LOADS
POL
B
+3.3V
LOADS
ENABLE
SEQUENCING
CONTROLLER
CPU
+VIN
ENABLE
TO OTHER POLs
STARTUP SEQUENCE:
ENABLE
ON
POL A
POL B
OFF
Settling
Delay
ON
OFF
TIME
Figure 9. Power Up/Down Sequencing Controller
If the power up/down timing needs to be closely controlled, each POL must
be characterized for start-up and down times. These often vary—one POL may
stabilize in 15 milliseconds whereas another takes 50 milliseconds. Another
problem is that the sequencing controller itself must be “already running” and
stabilized before starting up other circuits. If there is a glitch in the system,
the power up/down sequencer could get out of step with possible disastrous
results. Lastly, changing the timing may require reprogramming the logic
sequencer or rewriting software.
Sequence/Track Input
A different power sequencing solution is employed on MPS’s LSM2 DC/DC converter. After external input power is applied and the converter stabilizes, a high
impedance Sequence/Track input pin accepts an external analog voltage. The
output power voltage will then track this Sequence/Track input at a one-to-one
ratio up to the nominal set point voltage for that converter. This Sequencing
input may be ramped, delayed, stepped or otherwise phased as needed for
the output power, all fully controlled by the user’s simple external circuits. As a
direct input to the converter’s feedback loop, response to the Sequence/Track
input is very fast (milliseconds).
By properly controlling this Sequence pin, most operations of the discrete
On/Off logic sequencer may be duplicated. The Sequence pin system does not
use the converter’s Enable On/Off control (unless it is a master emergency shut
down system).
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MDC_LSM2 Series.D02∆ Page 12 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Power Phasing Architectures
Observe the simplified timing diagrams below. There are many possible power
phasing architectures and these are just some examples to help you analyze
your system. Each application will be different. Multiple output voltages may
require more complex timing than that shown here.
OUTPUT
VOLTAGE
POL A VOUT
These diagrams illustrate the time and slew rate relationship between two
typical power output voltages. Generally the Master will be a primary power
voltage in the system which must be present first or coincident with any
Slave power voltages. The Master output voltage is connected to the Slave’s
Sequence input, either by a voltage divider, divider-plus-capacitor or some
other method. Several standard sequencing architectures are prevalent. They
are concerned with three factors:
n The time relationship between the Master and Slave voltages
POL B VOUT
Coincident
VOUT Times
TIME
Figure 11. Proportional or Ratiometric Phasing (Identical VOUT Time)
n The voltage difference relationship between the Master and Slave
n The voltage slew rate (ramp slope) of each converter’s output.
For most systems, the time relationship is the dominant factor. The voltage
difference relationship is important for systems very concerned about possible
latchup of programmable devices or overdriving ESD diodes. Lower slew rates
avoid overcurrent shutdown during bypass cap charge-up.
In Figure 10, two POL’s ramp up at the same rate until they reach their
different respective final set point voltages. During the ramp, their voltages
are nearly identical. This avoids problems with large currents flowing between
logic systems which are not initialized yet. Since both end voltages are different, each converter reaches it’s setpoint voltage at a different time.
Figures 12 and 13 show both delayed start up and delayed final voltages
for two converters. Figure 12 is called “Inclusive” because the later starting
POL finishes inside the earlier POL. The timing in Figure 12 is more easily built
using a combined digital sequence controller and the Sequence/Track pin.
Figure 13 is the same strategy as Figure 12 but with an “exclusive” timing
relationship staggered approximately the same at power-up and power-down.
OUTPUT
VOLTAGE
POL A VOUT
OUTPUT
VOLTAGE
POL B VOUT
Delayed
VOUT Times
POL A VOUT
POL B VOUT
TIME
Figure 12. Staggered or Sequential Phasing—Inclusive (Fixed Delays)
Staggered
Times
+VOUT
OUTPUT
VOLTAGE
TIME
Not Drawn To Scale
Figure 10. Coincident or Simultaneous Phasing (Identical Slew Rates)
Figure 11 shows two POL’s with different slew rates in order to reach differing final voltages at about the same time.
POL A VOUT
POL B VOUT
Delayed
VOUT Times
TIME
Figure 13. Staggered or Sequential Phasing—Exclusive
(Fixed Cascaded Delays)
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MDC_LSM2 Series.D02∆ Page 13 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Operation
To use the Sequence pin after power start-up stabilizes, apply a rising external
voltage to the Sequence input. As the voltage rises, the output voltage will
track the Sequence input (gain = 1). The output voltage will stop rising when it
reaches the normal set point for the converter. The Sequence input may optionally continue to rise without any effect on the output. Keep the Sequence input
voltage below the converter’s input supply voltage.
Figure 15 shows a single POL and the same RC network. However, we have
added a FET at Q1 as an up/down control. When VIN power is applied to the
POL, Q1 is biased on, shorting out the Sequence pin. When Q1’s gate is biased
off, R1 charges C1 and the POL’s output ramps up at the R1-C1 slew rate. Note:
Q1’s gate would typically be controlled from some external digital logic.
+VIN
Use a similar strategy on power down. The output voltage will stay constant
until the Sequence input falls below the set point.
Any strategy may be used to deliver the power up/down ramps. The circuits
below show simple RC networks but you may also use operational amplifiers,
D/A converters, etc.
Circuits
The circuits shown in Figures 14 through 16 introduce several concepts when
using these Sequencing controls on Point-of-Load (POL) converters. These
circuits are only for reference and are not intended as final designs ready for
your application. Also, numerous connections are omitted for clarity.
+VIN
R1
SEQ/TRK
POL A
+VOUT = 5V
R1
SEQ/TRK
Q1
UP/DN
+VOUT = 5V
POL A
C1
–VIN
Figure 15. Self-Ramping Power Up
If you wish to have a ramped power down (rather than a step down), add a
small resistor in series with Q1’s drain.
Figure 16 shows both a RC ramp on Master POL A and a proportional tracking divider (R2 and R3) on POL B. We have also added an optional very small
noise filter cap at C2. Figure 16’s circuit corresponds roughly to Figure 11’s
timing for power up.
C1
+VIN
–VIN
R1
MAIN
RAMP
RATE
SEQ/TRK
POL A
+VOUT = 5V
POL B
+VOUT = 3.3V
C1
SEQ/TRK
POL B
–VIN
+VOUT = 3.3V
R2
Figure 14. Wiring for Simultaneous Phasing
Figure 14 shows a basic Master (POL A) and Slave (POL B) connected so the
POL B ramps up identically to POL A as shown in timing diagram, Figure 10. RC
network R1 and C1 charge up at a rate set by the R1-C1 time constant, giving
a roughly linear ramp. As POL A reaches 3.3VOUT (the setpoint of POL B), POL
B will stop rising. POL A then continues rising until it reaches 5V. R1 should be
significantly smaller than the internal bias current resistor from the Sequence
pin. Start with a 20kW value. We assume that the critical phase is only on
power up therefore there is no provision for ramped power down.
SEQ/TRK
R3
C2
–VIN
ANTI-NOISE FILTER, 1000pF TYP.
Figure 16. Proportional Phasing
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MDC_LSM2 Series.D02∆ Page 14 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
Guidelines for Sequence/Track Applications
[1] Leave the converter’s On/Off Enable control (if installed) in the On setting.
Normally, you should just leave the On/Off pin open.
[2] Allow the converter to stabilize (typically less than 20 mS after +VIN power
on) before raising the Sequence input. Also, if you wish to have a ramped
power down, leave +VIN powered all during the down ramp. Do not simply
shut off power.
[3] If you do not use the Sequence/Track pin, leave it open or tied to +VIN.
[4] Observe the Output slew rate relative to the Sequence input. A rough
guide is 2 Volts per millisecond maximum slew rate. If you exceed this
slew rate on the Sequence pin, the converter will simply ramp up at
it’s maximum output slew rate (and will not necessarily track the faster
Sequence input). The reason to carefully consider the slew rate limitation
is in case you want two different POL’s to precisely track each other.
[5] Be aware of the input characteristics of the Sequence pin. The high input
impedance affects the time constant of any small external ramp capacitor.
And the bias current will slowly charge up any external caps over time
if they are not grounded. The internal pull-up resistor to +VIN is typically
400kW to 1MW.
[8] If one converter is slaving to another master converter, there will be a very
short phase lag between the two converters. This can usually be ignored.
[9] You may connect two or more Sequence inputs in parallel from two converters. Be aware of the increasing pull-up bias current and reduced input
impedance.
[10] Any external capacitance added to the converter’s output may affect ramp
up/down times and ramp tracking accuracy.
Power Good Output
The Power Good Output consists of an unterminated BSS138 small signal
field effect transistor and a dual window comparator input circuit driving the
gate of the FET. Power Good is TRUE (open drain, high impedance state) if the
converter’s power output voltage is within about ±10% of the setpoint. Thus,
the PG TRUE condition indicates that the converter is approximately within
regulation. Since an overcurrent condition occurs at about 2% output voltage
reduction, the Power Good does not directly measure an output overcurrent
condition at rated maximum output current. However, gross overcurrent or an
output short circuit will set Power Good to FALSE (+0.2V saturation, low impedance condition).
Notice in the simplified Sequence/Track equivalent circuit (Figure 17) that
a blocking diode effectively disconnects this circuit when the Sequence/
Track pin is pulled up to +VIN or left open.
BSS138
Window
Comparator
PWM
CONTROLLER
+VOUT
FEEDBACK
User’s External
Logic
POWER
GOOD
HI
+VIN
+LOGIC
SUPPLY
External Pullup
Resistor
COMMON
LO
10mA
MAX.
POWER
OUTPUT
LOGIC
GROUND
1MΩ
+VIN
HI (Open Drain) = Power OK
LO (+0.2V Saturation) = Power not OK
TRIM
Figure 18. Equivalent Power Good Circuit
–
+
SEQ/
TRK
IN
Figure 17. Sequence/Track Simplified Equivalent Schematic
[6] Allow the converter to eventually achieve its full-rated setpoint output
voltage. Do not remain in ramp up/down mode indefinitely. The converter
is characterized and meets all its specifications only at the setpoint voltage (plus or minus any trim voltage). During the ramp-up phase, the converter is not considered fully in regulation. This may affect performance
with excessive high current loads at turn-on.
Using a simple connection to external logic (and returned to the converter’s
Common connection), the Power Good output is unterminated so that the user
may adapt the output to a variety of logic families. The PG pin may therefore
be used with logic voltages which are not necessarily the same as the input
or output power voltages. Install an external pullup resistor to the logic supply
voltage which is compatible with your logic system. When the Power Good is
out of limit, the FET is at saturation, approximately +0.2V output. Keep this
LOW (FALSE) pulldown current to less than 10mA.
Please note that Power Good is briefly false during Sequence ramp-up.
Ignore Power Good while in transition.
[7] The Sequence is a sensitive input into the feedback control loop of the
converter. Avoid noise and long leads on this input. Keep all wiring very
short. Use shielding if necessary. Consider adding a small parallel ceramic
capacitor across the Sequence/Track input (see Figure 16) to block any
external high frequency noise.
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MDC_LSM2 Series.D02∆ Page 15 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
MECHANICAL SPECIFICATIONS
Case C62
I/O CONNECTIONS
Pin Function P66
1
On/Off Control
2
+Input
3
Seq./Track
4
Common
5
+Output
6
Trim
7
Sense
8
Power Good*
10/16 Amp Models
1.30
(33.02)
0.34
(8.64)
0.085
(2.16)
SMT COPPER LEADS
COPLANAR 0.004
* Power Good is only installed for 10 and 16 Amp
“G” W3 models, otherwise pad 8 is not installed.
Dimensions are in inches (mm) shown for ref. only.
0.950 (24.13)
5 EQ. SP. @
0.190 (4.83)
0.120
(30.48)
3
4
5
6
Third Angle Projection
7
8
0.48 0.53
(12.19) (13.46)
2
0.430
(10.92)
1
BOTTOM VIEW
0.062
(1.57)
TYP.
Tolerances (unless otherwise specified):
.XX ± 0.02 (0.5)
.XXX ± 0.010 (0.25)
Angles ± 2˚
0.112 (2.84) TYP.
1.177
(29.90)
Dimensions are in inches (mm)
0.075
(1.91)
Components are shown for reference only.
0.048
(1.22)
Drawing not to scale
0.297
(7.54)
0.190 0.190 0.190 0.190
(4.83) (4.83) (4.83) (4.83)
0.190 (4.83)
0.405
(10.29)
8
7
6
5
4
3
1
0.430
(10.92)
2
1.177 (29.90)
RECOMMENDED PAD LAYOUT
Recommended Pad Size: 0.15 x 0.10 (3.81 x 2.54)
RECOMMENDED PAD LAYOUT
Recommended Pad Size: 0.15 x 0.10 (3.81 x 2.54)
www.murata-ps.com/support
MDC_LSM2 Series.D02∆ Page 16 of 17
LSM2 Series
Single Output, Non-Isolated
Selectable-Output POL DC/DC Converters
MECHANICAL SPECIFICATIONS (continued)
Case C63
I/O CONNECTIONS
Pin Function P67
1
On/Off Control
2
+Input
3
Seq./Track
4
Common
5
Trim
6
+Output
7
Power Good*
6 Amp Models
1.10
(27.94)
0.30
(7.62)
* Power Good is only included for 6 Amp “G”
models. Otherwise pad 7 is not installed.
SMT COPPER LEADS
COPLANAR 0.004
0.480 (12.19)
3 EQ. SP. @
0.160 (4.06)
0.190
(4.43)
3
4
5
6
7
0.350
(8.89)
0.05
(1.27)
BOTTOM VIEW
0.690
(17.53)
Dimensions are in inches (mm)
Murata Power Solutions, Inc.
129 Flanders Road, Westborough, MA 01581 U.S.A.
ISO 9001 and 14001 REGISTERED
6
5
4
3
0.350
(8.89)
1
7
1
0.09
(2.29)
TYP.
0.160 (4.06)
0.190 (4.43)
0.45
(11.43)
0.45
(11.43)
2
0.160 (4.06)
0.160 (4.06)
0.020 (0.51)
0.06 (1.52)
0.062(1.58) TYP.
0.06 (1.52)
0.15
(3.81)
2
0.062
(1.57)
0.090
(2.29)
0.05
(1.27)
1.10 (27.94)
RECOMMENDED PAD LAYOUT
Recommended Pad Size: 0.15 x 0.10 (3.81 x 2.54)
Drawing not to scale
0.15 (3.81)
Drawing not to scale
This product is subject to the following operating requirements
and the Life and Safety Critical Application Sales Policy:
Refer to: http://www.murata-ps.com/requirements/
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. Specifications are subject to change
without notice.
© 2018 Murata Power Solutions, Inc.
www.murata-ps.com/support
MDC_LSM2 Series.D02∆ Page 17 of 17
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