OKI-78SR [MURATA]
Fixed Output 1.5 Amp SIP DC/DC Converters; 固定输出1.5安培SIP DC / DC转换器
| 型号： | OKI-78SR |
| 厂家： | 
muRata |
| 描述： | Fixed Output 1.5 Amp SIP DC/DC Converters |
| 文件： | 总10页 (文件大小：424K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
OKI-78SR Series
s
Fixed Output 1.5 Amp SIP DC/DC Converters
PRODUCT OVERVIEW
Fabricated on a 0.41 by 0.65 inch (10.4 by 16.5
mm) Single Inline Package (SIP) module, the OKI-
78SR series are non-isolated switching regulator
(SR) DC/DC power converters for embedded ap-
plications. The fixed single output converters offer
both tight regulation and high efficiency directly
at the power usage site and are a direct plug-in
Based on fixed-frequency buck switching topology,
the high efficiency means very low heat and little
electrical noise, requiring no external components.
The ultra wide input range is 7 to 36 Volts DC.
Protection features include input undervoltage
and short circuit protection, overcurrent and over
temperature shut down. The OKI-78SR is designed
replacement for TO-220 package 78xx series linear to meet all standards approvals. RoHS-6 (no lead)
Typical unit
regulators. Typically, no extra outside components
are required.
hazardous material compliance is specified as
standard.
Two nominal output voltages are offered (3.3
and 5 VDC), each with 1.5 Amp maximum output.
FEATURES
■ Ultra wide 7 to 36 VDC input range
■ Fixed Outputs of 3.3 or 5 VDC up to 1.5 Amps
■ Vertical SIP-mount, small footprint package
■ “No heat sink” direct replacement for 3-terminal
78xx-series linear regulators
■ High efficiency with no external components
■ Short circuit protection
Contents
Page
Description, Connection Diagram, Photograph
Ordering Guide, Model Numbering, Product Labeling
Mechanical Specifications, Input/Output Pinout
Detailed Electrical Specifications
Performance Data and Oscillograms
Soldering Guidelines, Application Notes
1
2
3
4
5
9
■ Outstanding thermal derating performance
■ UL/EN/IEC 60950-1, 2nd Edition safety approvals
(pending)
Connection Diagram
+Vin
+Vout
tꢀ4XJUDIJOH
tꢀ'JMUFST
F1
Controller
tꢀ$VSSFOUꢀ4FOTF
External
DC
Power
Source
Reference and
Error Amplifier
Common
Common
Figure 1. OKI-78SR
Note: Murata Power Solutions strongly recommends an external input fuse, F1.
See specifications.
For full details go to
www.murata-ps.com/rohs
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 1 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
Performance Specifications and Ordering Guide
ORDERING GUIDE
Output
R/N (mVp-p) Regulation (Max.)
Input
Efficiency
Typ.
IOUT
IIN,
IIN,
VOUT
(Volts)
(Amps Power
max) (Watts)
VIN Nom. Range no load full load
Package
Root Model
Max.
Line
Load
(Volts) (Volts)
(mA)
(Amps) Min.
➀
0.41 x 0.65 x 0.3
1.5
1.5
24
24
5
0.48
0.69
84ꢀ 85.5ꢀ
89ꢀ 90.5ꢀ
OKI-78SR3.3/1.5-W36-C
3.3
5
4.95
7.5
40
0.25ꢀ
0.25ꢀ
7-36
7-36
(10.4 x 16.5 x 7.62)
0.41 x 0.65 x 0.3
5
OKI-78SR5/1.5-W36-C
75
0.25ꢀ
0.25ꢀ
(10.4 x 16.5 x 7.62)
➀ Dimensions are in inches (mm).
➁ All specifications are at nominal line voltage, Vout = nominal and full load, +25 ˚C., with no external capacitor,
unless otherwise noted.
Product Label
Because of the small size of these products, the product label contains a
character-reduced code to indicate the model number and manufacturing date
code. Not all items on the label are always used. Please note that the label dif-
fers from the product photograph on page 1. Here is the layout of the label:
Model Number
Product Code
I33115
OKI-78SR3.3/1.5-W36-C
OKI-78SR5/1.5-W36-C
I50115
The manufacturing date code is four characters:
XXXXXX
Product code
Revision level
First character – Last digit of manufacturing year, example 2009
Second character – Month code (1 through 9 and O through D)
Third character – Day code (1 through 9 = 1 to 9, 10 = O and
11 through 31 = A through Z)
Mfg.
date
code
YMDX Rev.
Figure 2. Label Artwork Layout
Fourth character – Manufacturing information
The label contains three rows of information:
First row – Murata Power Solutions logo
Second row – Model number product code (see table)
Third row – Manufacturing date code and revision level
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 2 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
MECHANICAL SPECIFICATIONS
0.30 (7.6)
0.16 (4.1)
0.41
(10.4)
C
L
0.06
(1.5)
REF
0.205
(5.2)
REF
0.65
(16.5)
Pin #3
0.13 (3.3)
0.05 (1.3)
Pin #1
0.030±0.002
0.100 (2.5)
0.200 (5.1)
Pin #1
PIN MATERIAL: COPPER ALLOY
PIN FINISH: PURE MATTE TIN 100-300 u"
OVER 75-150 u" NICKEL
Pin #1
Dimensions are in inches (mm shown for ref. only).
INPUT/OUTPUT CONNECTIONS
OKI-78SR
Third Angle Projection
Pin
Function
Positive Input
Common (Ground)
Positive Output
1
2
3
Tolerances (unless otherwise specified):
.XX 0.02 (0.5)
.XXX 0.010 (0.25)
Angles 1˚
Components are shown for reference only.
Figure 2. OKI-78SR Mechanical Outline
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 3 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
Physical
Performance and Functional Specifications
All specifications are typical unless noted. See Note 1
Outline Dimensions
Weight
See Mechanical Specifications [11]
0.07 ounces (2 grams)
UL/cUL 60950-1
CSA-C22.2 No. 60950-1
IEC/EN 60950-1, 2nd Edition
Input
Input Voltage Range
Recommended External Fuse
See Ordering Guide.
2 Amps fast blow
Safety
Reverse Polarity Protection (Note 9) None. Install an external fuse.
Absolute Maximum Ratings
Input Voltage, Continuous or transient 36 Volts max.
Not isolated. The input and output share a
common return.
Isolation (note 5)
Input Reverse Polarity Protection
None. Install external fuse.
4.85V. min., 6.0V. max (OKI-78SR3.3/1.5-W36)
6.5V. min., 7.5V. max. (OKI-78SR5/1.5-W36)
4.15V.min., 4.5V. max. (OKI-78SR3.3/1.5-W36)
3.5V. min., 5.0V. max. (OKI-78SR5/1.5-W36)
None
Start-Up Voltage
Current-limited. Devices can withstand sustained
short circuit without damage.
-40 to +125 deg. C.
Output Current
Undervoltage Shutdown (Note 13)
Storage Temperature
Overvoltage Shutdown
Internal Input Filter Type
Input Current:
Specification Notes:
Capacitive
(1) All specifications are typical unless noted. General conditions for Specifications are +25 deg.C ambient
temperature, Vin=nominal, Vout=nominal, full rated load. Adequate airflow must be supplied for extended
testing under power. See Derating curves.
Full Load Conditions
Inrush Transient
See Ordering Guide
0.16 A2Sec.
All models are tested and specified with no external capacitors. All models are stable and regulate within
spec under no-load conditions.
Shutdown Mode (Off, UV, OT)
Output in Short Circuit
No Load
1 mA
5 mA
5 mA
(2) Input Back Ripple Current is tested and specified over a 5 Hz to 20 MHz bandwidth. Input filtering is Cin=2 x
100 μF, Cbus=1000 μF, Lbus=1 μH. All caps are low ESR types.
0.8 Amps (OKI-78SR3.3/1.5-W36)
1.16 Amps (OKI-78SR5/1.5-W36)
10 mA pk-pk (OKI-78SR3.3/1.5-W36)
49 mA pk-pk (OKI-78SR5/1.5-W36)
(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. All Derating curves are presented near sea level
altitude. Be aware of reduced power dissipation with increasing altitude.
Low Line (Vin=Vmin, Vout=nom)
Reflected (Back) Ripple Current
(Note 2)
(4) Mean Time Before Failure is calculated using the Telcordia (Belcore) SR-332 Method 1, Case 3, ground fixed
conditions, Tpcboard=+25 deg.C, full output load, natural air convection.
Output
Output Voltage
See Ordering Guide
(5) The input and output are not isolated. They share a single COMMON power and signal return.
Output Current Range
Minimum Loading (Note 12)
0 to 1.5 Amps
No minimum load
5.15 Watts (OKI-78SR3.3/1.5-W36)
7.8 Watts (OKI-78SR5/1.5-W36)
4 ꢀ of Vnom
(6) Short circuit shutdown begins when the output voltage degrades approximately 2ꢀ from the selected
setting. Output current limit and short circuit protection are non-latching. When the overcurrent fault is
removed, the converter will immediately recover.
Maximum Output Power
(7) The output is not intended to sink appreciable reverse current.
(8) “Hiccup” overcurrent operation repeatedly attempts to restart the converter with a brief, full-current output.
If the overcurrent condition still exists, the restart current will be removed and then tried again. This short
current pulse prevents overheating and damaging the converter.
Accuracy (50ꢀ load)
Overvoltage Protection (Note 7)
Temperature Coefficient
Ripple/Noise (20 MHz bandwidth)
Line/Load Regulation
None
0.02ꢀ per ꢁC. of Vout range
See Ordering Guide and note 12
See Ordering Guide and note 10
See Ordering Guide and performance graphs
(9) Input Fusing: If reverse polarity is accidentally applied to the input, to ensure reverse input protection,
always connect an external input fast-blow fuse in series with the +Vin input. Use approximately twice the
full input current rating with nominal input voltage.
Efficiency
(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.
Maximum Capacitive Loading
Cap-ESR=0.001 to 0.01 Ohms
Cap-ESR >0.01 Ohms
Current Limit Inception (98ꢀ of Vout
setting, after warm up)
(11) CAUTION: Since the converter is mounted on the end by its pins, do not subject it to high vibration, shock or
acceleration.
300 μF
3300 μF
(12) Output noise may be further reduced by installing an external filter. Do not exceed the maximum output
capacitance. At zero output current and no external capacitor, the output may contain low frequency
components which exceed the ripple specification. The output may be operated indefinitely with no load.
3.5 Amps
Short Circuit Mode (Notes 6, 12)
Short Circuit Current Output
(13) The input must remain above the Undervoltage Shutdown (UVLO) voltage specification at all times to avoid
an unplanned turn off.
10 mA
Hiccup autorecovery upon overload removal.
(Note 8)
Continuous, no damage (output shorted to
ground)
The converter will start up if the external output
voltage is less than Vnominal.
Protection Method
Short Circuit Duration
Prebias Startup
Dynamic Characteristics
Dynamic Load Response (50ꢀ to 100ꢀ load step, no external caps)
di/dt = 1 A/μSec
Peak deviation
Switching Frequency
25 μSec settling time to within 2ꢀ of final value
100 mV
500 KHz
Environmental
Calculated MTBF (Note 4)
TBC
Operating Ambient Temperature Range
Full power, with derating [3]
Storage Temperature Range
Relative Humidity
-40 to +85 ꢁC. see derating curves.
-55 to +125 ꢁC.
to 85ꢀ/+85 ꢁC.
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 4 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
PERFORMANCE DATA – OKI-78SR3.3/1.5-W36
Efficiency vs. Line Voltage and Load Current @ +25˚C. (Vout = Vnom.)
Maximum Current Temperature Derating at sea level (Vin=7V. to 36V.)
2.00
1.00
0.00
100
90
80
70
60
50
40
30
20
10
0
VIN = 7V
VIN = 12V
VIN = 36V
65 LFM
20
25
30
35
40
45
50
55
60
65
70
75
80
85
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Ambient Temperature (ºC)
Load Current (Amps)
Output Ripple and Noise (Vin=7V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=12V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=36V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 5 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
PERFORMANCE DATA – OKI-78SR3.3/1.5-W36
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 6 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
PERFORMANCE DATA – OKI-78SR5/1.5-W36
Efficiency vs. Line Voltage and Load Current @ +25˚C. (Vout = Vnom.)
Maximum Current Temperature Derating at sea level (Vin=7V. to 36V.)
2.00
1.00
0.00
100
90
80
VIN = 7V
VIN = 12V
VIN = 36V
70
60
50
40
30
20
10
0
65 LFM
20
25
30
35
40
45
50
55
60
65
70
75
80
85
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Ambient Temperature (ºC)
Load Current (Amps)
Output Ripple and Noise (Vin=7V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=12V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
Output Ripple and Noise (Vin=36V, Vout=nominal, Iout=1.6A, Cload=0, Ta=+25˚C.,
ScopeBW=100MHz)
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 7 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
PERFORMANCE DATA – OKI-78SR5/1.5-W36
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=7V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=12V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=0.75A to 1.5A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
Step Load Transient Response (Vin=36V, Vout=nominal, Cload=0, Iout=1.5A to 0.75A,
Slew=1A/μS, Ta=+25˚C.) Trace 2=Vout, 100 mV/div. Trace 4=Iout, 0.5A/div.
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 8 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
Soldering Guidelines
Murata Power Solutions recommends the specifications below when installing these converters. These specifications vary depending on the solder type. Exceeding these specifica-
tions may cause damage to the product. Be cautious when there is high atmospheric humidity. We strongly recommend a mild pre-bake (100 ºC. for 30 minutes). Your production
environment may differ therefore please thoroughly review these guidelines with your process engineers.
Reflow Solder Operations for surface-mount products (SMT)
For Sn/Ag/Cu based solders:
Preheat Temperature
For Sn/Pb based solders:
Preheat Temperature
Time over Liquidus
Less than 1 ºC. per second
45 to 75 seconds
Less than 1 ºC. per second
60 to 75 seconds
Time over Liquidus
Maximum Peak Temperature 260 ºC.
Maximum Peak Temperature 235 ºC.
Cooling Rate Less than 3 ºC. per second
Cooling Rate
Less than 3 ºC. per second
APPLICATION NOTES
For best performance, we recommend installing a low-ESR capacitor
Input Fusing
immediately adjacent to the converter’s input terminals. The capacitor should
be a ceramic type such as the Murata GRM32 series or a polymer type. Initial
suggested capacitor values are 10 to 22 μF, rated at twice the expected maxi-
mum input voltage. Make sure that the input terminals do not go below the
undervoltage shutdown voltage at all times. More input bulk capacitance may
be added in parallel (either electrolytic or tantalum) if needed.
Certain applications and/or safety agencies may require fuses at the inputs of
power conversion components. Fuses should also be used when there is the
possibility of sustained input voltage reversal which is not current-limited. For
greatest safety, we recommend a fast blow fuse installed in the ungrounded
input supply line.
The installer must observe all relevant safety standards and regulations. For
safety agency approvals, install the converter in compliance with the end-user
safety standard.
Recommended Output Filtering
The converter will achieve its rated output ripple and noise with no additional
external capacitor. However, the user may install more external output capaci-
tance to reduce the ripple even further or for improved dynamic response.
Again, use low-ESR ceramic (Murata GRM32 series) or polymer capacitors.
Initial values of 10 to 47 μF may be tried, either single or multiple capacitors in
parallel. Mount these close to the converter. Measure the output ripple under
your load conditions.
Input Under-Voltage Shutdown and Start-Up Threshold
Under normal start-up conditions, converters will not begin to regulate properly
until the rising input voltage exceeds and remains at the Start-Up Threshold
Voltage (see Specifications). Once operating, converters will not turn off until
the input voltage drops below the Under-Voltage Shutdown Limit. Subsequent
restart will not occur until the input voltage rises again above the Start-Up
Threshold. This built-in hysteresis prevents any unstable on/off operation at a
single input voltage.
Use only as much capacitance as required to achieve your ripple and noise
objectives. Excessive capacitance can make step load recovery sluggish or
possibly introduce instability. Do not exceed the maximum rated output capaci-
tance listed in the specifications.
Users should be aware however of input sources near the Under-Voltage
Shutdown whose voltage decays as input current is consumed (such as
capacitor inputs), the converter shuts off and then restarts as the external
capacitor recharges. Such situations could oscillate. To prevent this, make
sure the operating input voltage is well above the UV Shutdown voltage AT ALL
TIMES.
Input Ripple Current and Output Noise
All models in this converter series are tested and specified for input reflected
ripple current and output noise using designated external input/output compo-
nents, circuits and layout as shown in the figures below. The Cbus and Lbus
components simulate a typical DC voltage bus. Please note that the values of
Cin, Lbus and Cbus will vary according to the specific converter model.
Start-Up Time
Assuming that the output current is set at the rated maximum, the Vin to Vout
Start-Up Time (see Specifications) is the time interval between the point when
the rising input voltage crosses the Start-Up Threshold and the fully loaded
regulated output voltage enters and remains within its specified regulation
band. Actual measured times will vary with input source impedance, external
input capacitance, input voltage slew rate and final value of the input voltage
as it appears at the converter.
TO
CURRENT
PROBE
OSCILLOSCOPE
+INPUT
-INPUT
LBUS
+
–
+
–
VIN
CBUS
CIN
These converters include a soft start circuit to moderate the duty cycle of its
PWM controller at power up, thereby limiting the input inrush current.
Recommended Input Filtering
C
C
IN = 2 x 100μF, ESR < 700mΩ @ 100kHz
BUS = 1000μF, ESR < 100mΩ @ 100kHz
The user must assure that the input source has low AC impedance to provide
dynamic stability and that the input supply has little or no inductive content,
including long distributed wiring to a remote power supply. The converter will
operate with no additional external capacitance if these conditions are met.
L
BUS = 1μH
Figure 2: Measuring Input Ripple Current
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21 May 2010 MDC_OKI-78SR-W36.A01 Page 9 of 10
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
In figure 3, the two copper strips simulate real-world printed circuit imped-
ances between the power supply and its load. In order to minimize circuit
errors and standardize tests between units, scope measurements should be
made using BNC connectors or the probe ground should not exceed one half-
inch and soldered directly to the test circuit.
Note that the temperatures are of the ambient airflow, not the converter
itself which is obviously running at higher temperature than the outside air.
Also note that “natural convection” is defined as very flow rates which are not
using fan-forced airflow. Depending on the application, “natural convection” is
usually about 30-65 LFM but is not equal to still air (0 LFM).
Murata Power Solutions makes Characterization measurements in a closed
cycle wind tunnel with calibrated airflow. We use both thermocouples and an
infrared camera system to observe thermal performance. As a practical matter,
it is quite difficult to insert an anemometer to precisely measure airflow in
most applications. Sometimes it is possible to estimate the effective airflow if
you thoroughly understand the enclosure geometry, entry/exit orifice areas and
the fan flowrate specifications.
COPPER STRIP
+OUTPUT
RLOAD
SCOPE
C1
C2
CAUTION: If you routinely or accidentally exceed these Derating guidelines,
the converter may have an unplanned Over Temperature shut down. Also, these
graphs are all collected at near Sea Level altitude. Be sure to reduce the derat-
ing for higher altitude.
-OUTPUT
COPPER STRIP
Output Fusing
C1 = 0.1μF CERAMIC
C2 = 10μF TANTALUM
The converter is extensively protected against current, voltage and temperature
extremes. However your output application circuit may need additional protec-
tion. In the extremely unlikely event of output circuit failure, excessive voltage
could be applied to your circuit. Consider using an appropriate fuse in series
with the output.
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3: Measuring Output Ripple and Noise (PARD)
Minimum Output Loading Requirements
All models regulate within specification and are stable under no load to full
load conditions. Operation under no load might however slightly increase
output ripple and noise.
Output Current Limiting
Current limiting inception is defined as the point at which full power falls below
the rated tolerance. See the Performance/Functional Specifications. Note par-
ticularly that the output current may briefly rise above its rated value in normal
operation as long as the average output power is not exceeded. This enhances
reliability and continued operation of your application. If the output current is
too high, the converter will enter the short circuit condition.
Thermal Shutdown
To prevent many over temperature problems and damage, these converters
include thermal shutdown circuitry. If environmental conditions cause the
temperature of the DC/DC’s to rise above the Operating Temperature Range
up to the shutdown temperature, an on-board electronic temperature sensor
will power down the unit. When the temperature decreases below the turn-on
threshold, the converter will automatically restart. There is a small amount of
hysteresis to prevent rapid on/off cycling.
Output Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop as the
output current demand increases. If the output voltage drops too low (approxi-
mately 98ꢀ of nominal output voltage for most models), the bias voltage may
shut down the PWM controller. Following a time-out period, the PWM will
restart, causing the output voltage to begin rising to its appropriate value. If the
short-circuit condition persists, another shutdown cycle will initiate. This rapid
on/off cycling is called “hiccup mode”. The hiccup cycling reduces the average
output current, thereby preventing excessive internal temperatures and/or
component damage.
CAUTION: If you operate too close to the thermal limits, the converter may
shut down suddenly without warning. Be sure to thoroughly test your applica-
tion to avoid unplanned thermal shutdown.
Temperature Derating Curves
The graphs in the previous section illustrate typical operation under a variety
of conditions. The Derating curves show the maximum continuous ambient
air temperature and decreasing maximum output current which is acceptable
under increasing forced airflow measured in Linear Feet per Minute (“LFM”).
Note that these are AVERAGE measurements. The converter will accept brief
increases in current or reduced airflow as long as the average is not exceeded.
The “hiccup” system differs from older latching short circuit systems
because you do not have to power down the converter to make it restart. The
system will automatically restore operation as soon as the short circuit condi-
tion is removed.
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfield, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
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.
© 2010 Murata Power Solutions, Inc.
www.murata-ps.com/locations
email: sales@murata-ps.com
21 May 2010 MDC_OKI-78SR-W36.A01 Page 10 of 10
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