www.murata-ps.com
UHE Series
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
Typical units
Housed in smaller, 1.6" x 2" x 0.40" (41 x 51 x 10.2mm)
packages carrying the standard 2" x 2" pinout, MPS’s new
UHE Series DC/DC Converters deliver more current/power
(up to 10A/30W) than currently available from either
package size.
FEATURES
The most I
OUT
/P
OUT
in this format
Lower priced than bricks
Small 1.6" x 2" x 0.4" plastic package
with standard 2" x 2" pinout
Output configurations:
1.2/1.5/1.8/2.5V
OUT
@ 10 Amps
3.3/5V
OUT
@ 25 Watts
5/12/15V
OUT
@ 30 Watts
Five input ranges from 9-75 Volts
Efficiencies as high as 91.5%
Stable no-load operation
Optional Sense pins for low V
OUT
Thermal shutdown, I/O protected
1500 Vdc I/O BASIC Insulation
UL/EN60950-1 certified (2nd Edition);
CE marked for Q48 models
RoHS compliant
PRODUCT OVERVIEW
The UHE 12-30W Series of high-efficiency,
isolated DC/DC’s provide output power ranging
from 10 Amps @ 1.2V to 2 Amps @ 15V. Offering
both 2:1 and 4:1 input voltage ranges, UHE’s meet
V
IN
requirements from 9 to 75 Volts.
Taking full advantage of the synchronous-
rectifier, forward topology, UHEs boast outstanding
efficiency (some models exceed 91%) enabling
full-power operation to ambient temperatures as
high as +60°C, without air flow. Assembled using
fully automated, SMT-on-pcb techniques, UHEs
provide stable no-load operation, excellent line
(±0.1%) and load (±0.15%) regulation, quick step
response (200μsec), and low output ripple/noise
(50-100mVp-p). Additionally, the UHEs unique
output design eliminates one of the topology’s few
shortcomings–output reverse conduction.
All devices feature full I/O fault protection
including: input overvoltage and undervoltage
shutdown, precise output overvoltage protection
(a rarity on low-voltage outputs), output current
limiting, short-circuit protection, and thermal
shutdown.
All UHE models incorporate a V
OUT
Trim function
and an On/Off Control pin (positive or negative
polarity). Low-voltage models (1.2V to 5V) offer
optional sense pins facilitating either remote load
regulation or current sharing for true N+1 redun-
dancy. All models are certified to the BASIC insula-
tion requirements of UL/EN60950-1 (2nd Edition),
and 48V
IN
(75V max.) models carry the CE mark.
Selected models are RoHS compliant (Reduction
of Hazardous Substances).
SIMPLIFIED SCHEMATIC
+INPUT
(1)
SWITCH
CONTROL
+OUTPUT
(6)
+SENSE
(5)
–OUTPUT
(7)
–SENSE
(8)
OVERVOLTAGE
COMPARATOR
–INPUT
(2)
THERMAL
SHUTDOWN
OPTO
ISOLATION
PWM
CONTROLLER
UVLO & OVLO
COMPARATORS
ON/OFF
CONTROL
(4)
OPTO
ISOLATION
REFERENCE &
ERROR AMP
V
OUT
TRIM
(9)
Typical topology is shown.
c
Optional comparator feedback. Contact MPS.
d
Sense pins are optional on 1.2-5V
OUT
models ("R" suffix).
For full details go to
www.murata-ps.com/rohs
*
Figure 1. Simplified Schematic
One phase of two is shown.
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21 Jun 2010
email: sales@murata-ps.com
MDC_UHE_12-30W Series.B14
Page 1 of 14
UHE Series
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
PERFORMANCE SPECIFICATIONS AND ORDERING GUIDE
➀
Model Family
(See model numbering
on page 13)
V
OUT
(Volts)
1.2
1.2
1.2
1.5
1.5
1.5
1.8
1.8
1.8
2.5
2.5
2.5
3.3
3.3
3.3
3.3
5
5
5
5
5
5
12
12
12
12
12
15
15
15
15
15
I
OUT
(Amps)
10
10
10
10
10
10
10
10
10
10
10
10
7.5
7.5
7.5
7.5
5
5
6
6
6
6
2.5
2.5
2.5
2.5
2.5
2
2
2
2
2
Output
R/N (mVp-p)➁
Typ.
Max.
80
80
80
55
55
70
50
50
65
70
90
80
80
50
60
50
80
65
55
125
65
65
100
60
70
70
70
100
70
120
120
120
80
80
90
75
100
120
90
125
100
100
70
90
70
100
100
80
165
100
100
120
100
100
100
100
150
100
Input
Regulation (Max.)
Line
Load
➃
V
IN
Nom.
(Volts)
Range
(Volts)
I
IN
➂
(mA/A)
Efficiency
Min.
81%
82.2%
81%
84%
82.5%
85.5%
83.5%
87.7%
87%
86.5%
88%
86.7%
85.5%
86%
87.5%
86.5%
87.5%
87.5%
88.5%
85.5%
87%
88%
88%
90%
87%
88%
88%
88%
90%
Typ.
83.5%
83%
83%
85.5%
84%
87%
85%
88.7%
88.5%
88%
90%
88.7%
88.2%
87.5%
90%
87%
89%
91%
90%
87.5%
89%
90%
90%
92%
89%
89.5%
90%
90%
92%
Package
(Case/
Pinout)
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51/52
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
C32, P51
UHE-1.2/10000-D12-C
UHE-1.2/10000-D24-C
UHE-1.2/10000-D48-C
UHE-1.5/10000-D12-C
UHE-1.5/10000-D24-C
UHE-1.5/10000-D48-C
UHE-1.8/10000-D12-C
UHE-1.8/10000-D24-C
UHE-1.8/10000-D48-C
UHE-2.5/10000-D12-C
UHE-2.5/10000-D24-C
UHE-2.5/10000-D48-C
UHE-3.3/7500-Q12-C
UHE-3.3/7500-Q48-C
UHE-3.3/7500-D48-C
UHE-3.3/7500-D48T-C
UHE-5/5000-Q12-C
UHE-5/5000-Q48-C
UHE-5/6000-Q12-C
UHE-5/6000-D48-C
UHE-5/6000-D48T-C
UHE-5/6000-Q48T-C
UHE-12/2500-Q12-C
UHE-12/2500-D12-C
UHE-12/2500-D24-C
UHE-12/2500-Q48-C
UHE-12/2500-D48-C
UHE-15/2000-D12-C
UHE-15/2000-Q12-C
UHE-15/2000-D24-C
UHE-15/2000-Q48-C
UHE-15/2000-D48-C
±0.1%
±0.36/0.9%
12
9-18
75/1.2
±0.1%
±0.25/0.9%
24
18-36
35/0.6
±0.1%
±0.3/0.625%
48
36-75
35/0.31
Please contact Murata Power Solutions for further information.
±0.1%
±0.15/0.625%
24
18-36
35/0.73
±0.1%
±0.15/0.625%
48
36-75
35/0.38
Please contact Murata Power Solutions for further information.
±0.1%
±0.15/0.625%
24
18-36
35/0.86
±0.1%
±0.15/0.625%
48
36-75
35/0.44
Please contact Murata Power Solutions for further information.
±0.075%
±0.15/0.5%
24
18-36
35/1.23
±0.1%
±0.15/0.5%
48
36-75
35/0.59
±0.2%
±0.15/0.3%
24
9-36
50/1.17
±0.35%
±0.5%
48
18-75
38/0.57
±0.2%
±0.5%
48
36-75
35/0.6
±0.2%
±0.5%
48
36-75
35/0.58
±0.1%
±0.15/0.3%
24
9-36
50/1.2
±0.05%
±0.15/0.3%
48
18-75
38/0.58
±0.075%
±0.15%
24
9-36
50/1.44
±0.2%
±0.25/0.5%
48
36-75
45/0.7
±0.2%
±0.5%
48
36-75
45/0.7
±0.08%
±0.15%
48
18-75
38/0.69
±0.1%
±0.5%
24
9-36
42/1.43
±0.2%
±0.3%
12
9-18
90/2.81
±0.2%
±0.3%
24
18-36
55/1.39
±0.1%
±0.5%
48
18-75
30/0.6
±0.2%
±0.3%
48
36-75
30/0.7
±0.2%
±0.3%
12
9-18
110/2.81
±0.05%
±0.15%
24
9-36
50/1.4
±0.2%
±0.3%
24
18-36
70/1.39
±0.1%
±0.5%
48
18-75
45/0.69
±0.2%
±0.3%
48
36-75
35/0.7
c
Typical at T
A
= +25°C under nominal line voltage and full-load conditions, unless noted.
d
Ripple/Noise (R/N) is tested/specified over a 20MHz bandwidth. All models are specified with
an external 0.47μF multi-layer ceramic capacitor installed across their output pins.
e
Nominal line voltage, no-load/full-load conditions.
f
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
(with/without sense option) is varied from its nominal/midpoint value to either extreme.
MECHANICAL SPECIFICATIONS
INPUT/OUTPUT CONNECTIONS
Pin
Function P51
1
2
3
4
5
6
7
8
9
+Input
–Input
No Pin
On/Off Control
No Pin
+Output
–Output
No Pin
Trim
Dimensions are in inches (mm) shown for ref. only.
2.00
(50.8)
PLASTIC CASE
0.40
(10.2)
STANDOFF
0.020 (0.5)
Function P52
+Input
–Input
No Pin
On/Off Control
Sense*
+Output
–Output
–Sense*
Trim
Third Angle Projection
Tolerances (unless otherwise specified):
.XX ± 0.02 (0.5)
.XXX ± 0.010 (0.25)
Angles ± 2˚
Components are shown for reference only.
0.200
(5.1)
0.20 MIN
(5.08)
0.040 ±0.001 DIA.
(1.016 ±0.025)
1.800
(45.72)
0.10
(2.54)
0.200
(5.1)
5
6
1
2
7
8
9
0.400 (10.16)
2 EQ. SP. @
0.200 (5.08)
0.400
(10.2)
1.60
(40.6)
* Pins 5 and 8 are installed for optional R-suffix versions of 1.2-5V
OUT
models.
If installed, always connect the sense pins either to a remote load or to their
respective V
OUT
pin.
See page 13 for complete Part Number structure & ordering details.
0.400
(10.16)
3
4
0.100
(2.5)
BOTTOM VIEW
0.20
(5.1)
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21 Jun 2010
email: sales@murata-ps.com
MDC_UHE_12-30W Series.B14
Page 2 of 14
UHE Series
Performance/Functional Specifications
Input
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
Output
Typical @ T
A
= +25°C under nominal line voltage and full-load conditions, unless noted.
➀ ➁
Input Voltage Range:
D12 Models (start up at 10V max.)
Q12 Models (start up at 10V max.)
D24 Models
Q48 Models
D48 Models
Overvoltage Shutdown:
D12 Models
Q12/D24 Models
D48/Q48 Models
Start-Up Threshold:
➁
D12/Q12 Models
D24/Q48 Models
D48 Models
Undervoltage Shutdown:
➁
D12/Q12 Models
D24/Q48 Models
D48 Models
Input Current:
Normal Operating Conditions
Standby Mode (Off, OV, UV)
Input Reflected Ripple Current
➂
Input Filter Type
Reverse-Polarity Protection
Remote On/Off Control (Pin 4):
➃
Positive Logic (Standard)
9-18 Volts (12V nominal)
9-36 Volts (24V nominal)
18-36 Volts (24V nominal)
18-75 Volts (48V nominal)
36-75 Volts (48V nominal)
18.5-23 Volts
37-42 Volts
Not applicable
9.4-10 Volts
15.5-18 Volts
33.5-36 Volts
7.0-8.8 Volts
15-17 Volts
32-35.5 Volts
See Ordering Guide
5mA
2.5-10mAp-p
LC or Pi type
Brief duration, 5A maximum
On = open, open collector, or to +15V
applied. I
IN
= 2.6mA max.
Off = pulled low to 0-0.8V. I
IN
= 2mA max.
On = pulled low to 0-0.8V. I
IN
= 6mA max.
Off = open, open collector or to +15V
applied. I
IN
= 1mA max.
Output
Overvoltage Protection:
1.2V Outputs
1.5V Outputs
1.8V Outputs
2.5V Outputs
3.3V Outputs
5V Outputs
12V Outputs
15V Outputs
Maximum Capacitive Loading:
(Low ESR capacitor)
Magnetic feedback
1.5-2.1 Volts
1.8-2.4 Volts
2.2-2.8 Volts
2.8 to 3.2 Volts
4 to 4.8 Volts
6.1-7.5 Volts
12.7-13.5 Volts
15.8-16.2 Volts
10,000μF (1.2-5V
OUT
)
2,000μF (12-15V
OUT
)
Dynamic Characteristics
Dynamic Load Response:
(50-100% load step to ±3% V
OUT
)
Start-Up Time:
➇
V
IN
to V
OUT
and On/Off to V
OUT
UHE-15/2000-Q12
Switching Frequency
MTBF
➈
Operating Temperature (Ambient):
➉
(see Derating Curves)
Thermal Shutdown
Storage Temperature
Flammability
Dimensions
Case Material
Pin Material
Weight
Primary to Secondary Insulation Level
200μsec maximum
➇
8msec typical
15msec maximum
30mS typ., 50mS max.
150-350kHz (model dependent)
Environmental
TBC million hours
–40 to +85°C with Derating
+115°C to +130°C
–55 to +125°C
UL 94 V-0
Physical
Negative Logic ("N" Suffix Models)
1.6" x 2" x 0.40" (40.64 x 50.8 x 10.16mm)
Diallyl Phthalate
Gold-plated copper alloy
1.51 ounces (46.9 grams)
Basic
V
OUT
Accuracy (50% load):
Initial
Temperatue Coefficient
Extreme
(5)
Minimum Loading for Specification:
➁
Ripple/Noise (20MHz BW)
➀
Line/Load Regulation
Efficiency
V
OUT
Trim Range
(6)
Remote Sense Compensation
➁
Isolation Voltage:
Input-to-Output
Isolation Capacitance
Isolation Resistance
Current Limit Inception (@98%V
OUT
):
➆
10 Amp Models
7.5 Amp Models
5/6 Amp Models
2.5 Amp Models
2.0 Amp Models
Short Circuit Current (Hiccup)
±1.5%
±0.02% per °C
±3%
No load
See Ordering Guide
See Ordering Guide
See Ordering Guide
±5% minimum (±10% for T models)
±5%
1500Vdc minimum (BASIC)
650pF
100M:
12-15 Amps
8.2-11.5 Amps
6.5-8.5 Amps
2.6-4 Amps
2.1-3 Amps
1.5-2.3 Amps
➀
All models are tested and specified with a single, external, 0.47μF, multi-layer ceramic output
capacitor and no external input capacitors, unless otherwise noted. All models will effectively
regulate under no-load conditions (with perhaps a slight increase in output ripple/noise).
➁
See Technical Notes/Performance Curves for additional explanations and details.
➂
Input Ripple Current is tested/specified over a 5-20MHz bandwidth with an external 33μF input
capacitor and a simulated source impedance of 220μF and 12μH. See I/O Filtering, Input Ripple
Current and Output Noise for details.
➃
The On/Off Control is designed to be driven with open-collector (or equivalent) logic or the applica-
tion of appropriate voltages (referenced to –Input (pin 2)). Applying a voltage to the On/Off Control
pin when no input voltage is applied to the converter can cause permanent damage. See Remote
On/Off Control for more details.
➄
Extreme Accuracy refers to the accuracy of either trimmed or untrimmed output voltages over all
normal operating ranges and combinations of input voltage, output load and temperature.
➅
Tie the Output Trim pin (pin 9) to +Output (pin 6) for maximum trim down or to –Output (Output
Return/Common, pin 7) for maximum trim up. See Output Trimming for detailed trim equations.
➆
The Current-Limit-Inception point is the output current level at which the converter's power-limiting
circuitry drops the output voltage 2% from its initial value. See Output Current Limiting and
Short-Circuit Protection for more details.
➇
For Start-Up-Time specifications, output settling time is defined as the output voltage having
reached ±1% of its final value at maximum load current.
➈
MTBF’s are calculated using TELCORDIA SR-332 Method 1 Case, ground fixed, +25°C ambient air
and full-load conditions. Contact MPS for demonstrated life-test data.
➉
All models are fully operational and meet all published specifications, including "cold start," at –40°C.
Use only as much output filtering as needed
and no more.
Larger caps (especially low-ESR ceramic
types) may slow transient response or degrade dynamic performance. Thoroughly test your system
with all components installed.
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21 Jun 2010
email: sales@murata-ps.com
MDC_UHE_12-30W Series.B14
Page 3 of 14
UHE Series
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
Absolute Maximum Ratings
Input Voltage:
Continuous:
D12 Models
D24/Q12 Models
D48/Q48 Models
Transient (100msec):
D12 Models
D24/Q12 Models
D48/Q48 Models
On/Off Control (pin 4) Max. Voltages
Referenced to –Input (pin 2)
No Suffix
"N" Suffix
Input Reverse-Polarity Protection
Output Current
23 Volts
42 Volts
81 Volts
25 Volts
50 Volts
100 Volts
Input Undervoltage Shutdown and Start-Up Threshold
Under normal start-up conditions, devices will not begin to regulate until
the ramping-up input voltage exceeds the Start-Up Threshold Voltage. Once
operating, devices will not turn off until the input voltage drops below the
Undervoltage Shutdown limit. Subsequent re-start will not occur until the input
is brought back up to the Start-Up Threshold. This built in hysteresis prevents
any unstable on/off situations from occurring at a single input voltage.
Start-Up Time
The V
IN
to V
OUT
Start-Up Time is the interval of time between the point at which
the ramping input voltage crosses the Start-Up Threshold 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/output
capacitance, and load. The UHE Series implements a soft start circuit that limits
the duty cycle of its PWM controller at power up, thereby limiting the input
inrush current.
The On/Off Control to V
OUT
start-up time assumes the converter has its
nominal input voltage applied but is turned off via the On/Off Control pin. The
specification defines the interval between the point at which the converter is
turned on and the fully loaded output voltage enters and remains within its
specified accuracy band. Similar to the V
IN
to V
OUT
start-up, the On/Off Control
to V
OUT
start-up time is also governed by the internal soft start circuitry and
external load capacitance.
The difference in start up time from V
IN
to V
OUT
and from On/Off Control to
V
OUT
is therefore insignificant.
Input Overvoltage Shutdown
All D12/Q12 and D24 Models of the UHE DC/DC converters are equipped with
Input Overvoltage Protection. Input voltages exceeding the input overvoltage
shutdown specification listed in the Performance/Functional Specifications will
cause the device to shutdown. A built-in hysteresis for all models will not allow
the converter to restart until the input voltage is sufficiently reduced.
All 48V
IN
models have this overvoltage shutdown function disabled because
of requirements for withstanding brief input surges to 100V for up to 100μsec
without output voltage interruption.
Please contact MPS to have input overvoltage shutdown for D48/Q48
models enabled.
Input Source Impedance
UHE converters must be driven from a low ac-impedance input source. The
DC/DC's performance and stability can be compromised by the use of highly
inductive source impedances. The input circuit shown in Figure 2 is a practical
solution that can be used to minimize the effects of inductance in the input
traces. For optimum performance, components should be mounted close to
the DC/DC converter. If the application has a high source impedance, low V
IN
models can benefit of increased external input capacitance.
I/O Filtering, Input Ripple Current, and Output Noise
All models in the UHE 12-30 Watt DC/DC Converters are tested/specified for in-
put reflected ripple current and output noise using the specified external input/
output components/circuits and layout as shown in the following two figures.
External input capacitors (C
IN
in Figure 2) serve primarily as energy-storage
elements, minimizing line voltage variations caused by transient IR drops
+15 Volts
+7 Volts
Current must be <5 Amps. Brief
duration only. Fusing recommended.
Current limited. Devices can
withstand sustained output short
circuits without damage.
+100°C
–55 to +125°C
See soldering specifications
Case Temperature
Storage Temperature
Lead Temperature (soldering, 10 sec.)
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 Specifications Table is not implied.
T E C H N I C A L
N O T E S
Input Fusing
Certain applications and/or safety agencies may require the installation of
fuses at the inputs of power conversion components. Fuses should also be
used if the possibility of sustained, non-current-limited, input-voltage polarity
reversals exists. For MPS’s UHE 12-30 Watt DC/DC Converters, you should use
slow-blow type fuses, installed in the ungrounded input supply line, with values
no greater than the following.
Model
Output/Input
1.2 V
OUT
1.5 V
OUT
1.8 V
OUT
2.5 V
OUT
3.3 V
OUT
5 V
OUT
12 V
OUT
15 V
OUT
D12
3
4
5
5
--
--
6
6
Fuse Values in Amps
Q12
--
--
--
--
7.5
5
3
3
D24
2
2
2.5
2.5
-
-
3
3
Q48
--
--
--
--
3
3
5
5
D48
1
1
1
1
1.5
2
2
2
All relevant national and international safety standards and regulations must be
observed by the installer. For system safety agency approvals, the converters
must be installed in compliance with the requirements of the end-use safety
standard, e.g. IEC/EN/UL60950-1.
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21 Jun 2010
email: sales@murata-ps.com
MDC_UHE_12-30W Series.B14
Page 4 of 14
UHE Series
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
in conductors from backplane to the DC/DC. Input caps should be selected
for bulk capacitance (at appropriate frequencies), low ESR, and high rms-
ripple-current ratings. The switching nature of DC/DC converters requires that
dc voltage sources have low ac impedance as highly inductive source imped-
ance can affect system stability. In Figure 2, C
BUS
and L
BUS
simulate a typical
dc voltage bus. Your specific system configuration may necessitate additional
considerations.
TO
OSCILLOSCOPE
CURRENT
PROBE
+INPUT
+
V
IN
–
–INPUT
C
IN
= 33μF, ESR < 700m @ 100kHz
C
BUS
= 220μF, ESR < 100m @ 100kHz
L
BUS
= 12μH
C
BUS
L
BUS
C
IN
Floating Outputs
Since these are isolated DC/DC converters, their outputs are "floating" with
respect to their input. Designers will normally use the –Output (pin 7) as the
ground/return of the load circuit. You can, however, use the +Output (pin 6) as
ground/return to effectively reverse the output polarity.
Minimum Output Loading Requirements
UHE converters employ a synchronous-rectifier design topology and all models
regulate within spec and are stable under no-load to full load conditions.
Operation under no-load conditions however might slightly increase the output
ripple and noise.
Thermal Shutdown
These UHE converters are equipped with thermal-shutdown circuitry. If envi-
ronmental conditions cause the internal temperature of the DC/DC converter to
rise above the designed operating temperature, a precision temperature sensor
will power down the unit. When the internal temperature decreases below the
threshold of the temperature sensor, the unit will self start. See Performance/
Functional Specifications.
Output Overvoltage Protection
UHE output voltages are monitored for an overvoltage condition via magnetic
feedback. The signal is coupled to the primary side and if the output voltage
rises to a level which could be damaging to the load, the sensing circuitry will
power down the PWM controller causing the output voltages to decrease. Fol-
lowing a time-out period the PWM will restart, causing the output voltages to
ramp to their appropriate values. If the fault condition persists, and the output
voltages again climb to excessive levels, the overvoltage circuitry will initiate
another shutdown cycle. This on/off cycling is referred to as "hiccup" mode.
Contact MPS for an optional output overvoltage monitor circuit using a
comparator which is optically coupled to the primary side thus allowing tighter
and more precise control.
Current Limiting
As soon as the output current increases to 10% to 50% above its rated value,
the DC/DC converter will go into a current-limiting mode. In this condition, the
output voltage will decrease proportionately with increases in output current,
thereby maintaining somewhat constant power dissipation. This is commonly
referred to as power limiting. Current limit inception is defined as the point at
which the full-power output voltage falls below the specified tolerance. See
Performance/Functional Specifications. If the load current, being drawn from
the converter, is significant enough, the unit will go into a short circuit condition
as specified under “Performance.”
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, the
magnetically coupled voltage used to develop primary side voltages will also
drop, thereby shutting down the PWM controller. Following a time-out period,
the PWM will restart causing the output voltages to begin ramping to their
appropriate values. If the short-circuit condition persists, another shutdown
cycle will be initiated. This on/off cycling is referred to as “hiccup” mode. The
hiccup cycling reduces the average output current, thereby preventing internal
temperatures from rising to excessive levels. The UHE is capable of enduring
an indefinite short circuit output condition.
Figure 2. Measuring Input Ripple Current
In critical applications, output ripple/noise (also referred to as periodic and
random deviations or PARD) may be reduced below specified limits using filter-
ing techniques, the simplest of which is the installation of additional external
output capacitors. These output caps function as true filter elements and
should be selected for bulk capacitance, low ESR and appropriate frequency
response. All external capacitors should have appropriate voltage ratings and
be located as close to the converter as possible. Temperature variations for all
relevant parameters should also be taken carefully into consideration.
The most effective combination of external I/O capacitors will be a function
of line voltage and source impedance, as well as particular load and layout
conditions. Our Applications Engineers can recommend potential solutions and
discuss the possibility of our modifying a given device's internal filtering to
meet your specific requirements. Contact our Applications Engineering Group
for additional details.
+SENSE
+OUTPUT
COPPER STRIP
C1
C2
SCOPE
R
LOAD
–OUTPUT
–SENSE
COPPER STRIP
C1 = 0.47μF CERAMIC
C2 = NA
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3. Measuring Output Ripple/Noise (PARD)
In Figure 3, the two copper strips simulate real-world pcb impedances
between the power supply and its load. In order to minimize measurement errors,
scope measurements should be made using BNC connectors, or the probe
ground should be less than ½ inch and soldered directly to the fixture.
www.murata-ps.com
21 Jun 2010
email: sales@murata-ps.com
MDC_UHE_12-30W Series.B14
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Special Edition for Assessment Centres
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