ease of application with versatility. The pin pattern
is based on the popular industry standard, but two
additional pins may optionally be fitted to provide
a variety of features not commonly found on units
of this type. High efficiency enables full rating to
be achieved in a small package without heat-
sinking, and a high surge capability will provide
for start-up and transient loads, whilst being
thermally protected against sustained overload.
Overload protection of the “constant current” type
ensures start-up into complex load conditions. The
copper case achieves efficient heat transfer and
screening. The product range has been recog-
nised by Underwriters Laboratory (UL) to UL 1950
for operational insulation, file number E151252
applies.
70
ISOLATION CHARACTERISTICS
Parameter
Conditions
Isolation test voltage
Resistance
Flash tested for 1 second
VISO = 500VDC
Min.
1500
1
Typ.
Max.
Units
VDC
GΩ
ABSOLUTE MAXIMUM RATINGS
Input voltage, 24V input types
Input voltage, 48V input types
Output voltage
Output trim control
Synchronisation/shutdown control
-0.5V to 40V
3
-0.5V to 80V
3
-0.3V to regulated voltage
-1V to +30V
±15V relative to input return
For full details go to
www.murata-ps.com/rohs
1. Parts ending with EiC have optional TRIM and SS pins fitted.
2. Calculated using MIL-HDBK-217F with nominal input voltage at full load.
3. Absolute maximum value for 30 seconds. Prolonged operation may damage the product.
All specifications typical at T
A
=25°C, nominal input voltage and rated output current unless otherwise specified.
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KDC_NPH25S.H01
Page 1 of 8
NPH25S Series
Isolated 25W Single Output DC/DC Converters
CONTROL CHARACTERISTICS
Parameter
Voltage trimming range
1
Remote switch input (voltage relative to
input negative)
1
Start delay
Synchronisation
1
Switching frequency
Conditions
At rated load, trim control at either output
Not operating
Operating, open circuit voltage
Time from application of valid input voltage to output being in specifi-
cation
Specified drive signal
Min.
±10
-15
9
Typ.
0
10
25
Max.
1.5
11
50
440
395
Units
%
V
ms
kHz
kHz
320
330
350
TEMPERATURE CHARACTERISTICS
Parameter
Conditions
Case temperature
Storage
Relative humidity
Thermal protection
Full load
Absolute Max. internal temperature
Non condensing 85ºC
Operates at case temperature
Min.
-40
-40
110
Typ.
Max.
110
125
85
Units
ºC
%
ºC
THERMAL CHARACTERISTICS
UL 1950 recognition:
Max. permissable loads for a given ambient temperature for any NPH25S model.
Temperature (ºC)
40
50
60
70
Power (W)
25.0
22.2
19.4
16.6
Temperature (ºC)
80
85
90
Power (W)
13.9
12.5
11.1
Max. power rating with case temperature maintained by external means (e.g. forced air cooling).
Part Number
NPH25S2403XXX
NPH25S2405XXX
NPH25S2412XXX
NPH25S2415XXX
NPH25S4803XXX
NPH25S4805XXX
NPH25S4812XXX
NPH25S4815XXX
100ºC
24
25
30
30
25
25
30
30
Case Temperature
105ºC
20
22
24
27
20
24
29
30
110ºC
15
18
21
22
16
20
24
26
Units
W
W
THERMAL PERFORMANCE
24V Input
48V Input
1. Optional - where fitted.
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KDC_NPH25S.H01
Page 2 of 8
NPH25S Series
Isolated 25W Single Output DC/DC Converters
APPLICATION NOTES
OUTPUT VOLTAGE ADJUSTMENT
The trim resistor equations are:
Rup = (R/Vup) - S kΩ
Rdown = (L x T ) - T - S kΩ
V
down
V
NOM
S
T
R
L
3.4
22.2973
10.1351
17.9994
-1.6241
5.1
20.59761
9.36255
24.49487
-2.48374
12.1
28.79096
15.42373
94.9661
-5.942857
15.1
39.95902
20.77869
147.7314
-7.990244
TRIM UP
+V
IN
TRIM
+V
OUT
TRIM DOWN
+V
IN
R
DOWN
R
UP
+V
OUT
NPH25S
NPH25S
TRIM
-
V
OUT
When the output voltage is trimmed up, output current must be derated so that the maximum output power is not exceeded.
Example to decrease output voltage of NPH25S4805EiC by 0.1V:
R
DOWN
= -2.48374 x 9.36255 - 9.36255 - 20.59761 = 203.18kΩ
-0.1
-
V
OUT
(
)
SET VOLTAGE
The output voltage of all units is set to 100mV above nominal, to offset resistive losses and thus assist with worst case error calculations. For the EiC versions, this
allowance can be altered with a single fixed resistor, connected from the trimming pin to one of the output pins.
SHUTDOWN
When the shutdown pin (SS) is shorted to the negative input, the converter will
stop. Its current consumption will then be less than 1mA at nominal supply
voltage. The voltage must be less than 1.5V to ensure that the unit stops, and
must be able to sink at least 1mA.
The unit will restart if the control pin is left open circuit or raised to a value
close to its normal open circuit voltage. This is typically 10V. Note however,
that the unit will not meet specification while a significant current drain from
this pin remains.
If the shutdown pin is to be connected to a long wire, it is recommended that a
capacitor decouples the pin to the supply common in order to avoid the risk of
injecting noise into the converter circuit. A series resistor may also be helpful.
Values of 10nF and 1kΩ may be used.
Many NPH series converters may be switched together simply by linking the
primary control pins. The primary common pins must also be linked.
FREQUENCY CONTROL
If the primary side dc control voltage is pulled away from its open circuit
voltage, the converter frequency will be changed, approximately in proportion
to the voltage. With +8.5VDC voltage to SS pin, the typical switching frequency
will be 300kHz. If this is raised to 15VDC, the switching frequency will typically
be 510kHz. The frequency may thus be moved away from a sensitive value or
into a safe area. Deviation of at least –10% to +30% is achievable, though the
efficiency will decline with significant changes. Also note that if the frequency
is lowered, the switching frequency component of output ripple will increase.
Since the design uses no large electrolytic capacitors, any use of a lower
frequency must allow for the effects of increased ripple. Additional external
filtering may be required.
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KDC_NPH25S.H01
Page 3 of 8
NPH25S Series
Isolated 25W Single Output DC/DC Converters
APPLICATION NOTES (continued)
SYNCHRONIZATION
The converter frequency may be synchronised to an external frequency by connecting a negative going pulse to the SS pin. The drive signal is typically
8V to 12V amplitude and 100ns to 200ns duration. A suitable circuit consists of a CMOS timer (TLC555) connected as an oscillator or as a pulse shaper.
Its logic output (not the discharge output) should be connected via a 4.7nF capacitor to the converter pin. The synchronised frequency is above the free
running value. However, the free running frequency can be lowered, so that sychronisation may include frequencies near or below the natural value. An
example of a practical circuit is shown below, which uses a zener diode to lower the natural frequency. Several converters of this family may be syn-
chronised from the same reference provided the waveform can be maintained by the use of an adequate driver circuit. If the rise time is more than 20ns,
for example, synchronisation may not be achieved over the specified frequency range.
For best efficiency, set the frequency within the specified range of its natural state.
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Voltage’, ‘Dielectric Withstand Voltage’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test voltage,
applied for a specified time, across a component designed to provide electrical isolation, to verify the integrity of that isolation.
Murata Power Solutions NPH25S series of DC/DC converters are all 100% production tested at their stated isolation voltage. This is 1500 VDC for 1 second.
A question commonly asked is, “What is the continuous voltage that can be applied across the part in normal operation?”
The NPH25S series has been recognized by Underwriters Laboratory, both input and output should normally be maintained within SELV limits i.e. less than 42.4V peak, or 60VDC.
The isolation test voltage represents a measure of immunity to transient voltages and the part should never be used as an element of a safety isolation system. The part could be
expected to function correctly with several hundred volts offset applied continuously across the isolation barrier; but then the circuitry on both sides of the barrier must be regarded
as operating at an unsafe voltage and further isolation/insulation systems must form a barrier between these circuits and any user-accessible circuitry according to safety standard
requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component can actually degrade isolation capability, to a lesser or greater degree depending on materi-
als, construction and environment. While manufactured parts can withstand several times the stated test voltage, the isolation capability does depend on the wire insulation. Any
material, including this enamel (typically polyurethane) is susceptible to eventual chemical degradation when subject to very high applied voltages thus implying that the number of
tests should be strictly limited. We therefore strongly advise against repeated high voltage isolation testing, but if it is absolutely required, that the voltage be reduced by 20% from
specified test voltage.
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KDC_NPH25S.H01
Page 4 of 8
NPH25S Series
Isolated 25W Single Output DC/DC Converters
EMC FILTERING AND SPECTRA
FILTERING
The module includes a basic level of filtering, sufficient for many applications. Where lower noise levels are desired, filters can easily be added to achieve any required
noise performance.
A DC/DC converter generates noise in two principle forms: that which is radiated from its body and that conducted on its external connections. There are three separate
modes of conducted noise: input differential, output differential and input-output.
This last appears as common mode at the input and the output, and cannot therefore be removed by filtering at the input or output alone. The first level of filtering is to
connect a capacitor between input and output returns, to reduce this form of noise. It typically contains high harmonics of the switching frequency, which tend to appear
as spikes on surrounding circuits. The voltage rating of this capacitor must match the required isolation voltage. (Due to the great variety in isolation voltage and required
noise performance, this capacitor has not been included within the converter.)
Input ripple is a voltage developed across the internal Input decoupling capacitor. It is therefore measured with a defined supply source impedance. Although simple series
inductance will provide filtering, on its own it can degrade the stability. A shunt capacitor is therefore recommended across the converter input terminals, so that it is fed
from a low impedance.
If no filtering is required, the inductance of long supply wiring could also cause a problem, requiring an input decoupling capacitor for stability. An electrolytic will perform
well in these situations. The input-output filtering is performed by the common-mode choke on the primary. This could be placed on the output, but would then degrade the
regulation and produce less benefit for a given size, cost, and power loss.
Radiated noise is present in magnetic and electrostatic forms. The latter is suppressed by the metal case, which is connected to the output return, typically a zero-volt
point. Thanks to the small size of these units, neither form of noise will be radiated “efficiently”, so will not normally cause a problem. Any question of this kind usually
better repays attention to conducted signals.
EMC FILTER AND VALUES TO OBTAIN SPECTRA AS SHOWN
Component reference
C1
NPH25S2403
NPH25S2405
NPH25S2412
NPH25S2415
NPH25S4803
NPH25S4805
NPH25S4812
NPH25S4815
10μF 100V
10μF 100V
10μF 100V
10μF 100V
10μF 100V
10μF 100V
10μF 100V
10μF 100V
C2
2.2μF 63V
2.2μF 63V
2.2μF 63V
2.2μF 63V
Not required
Not required
Not required
Not required
C3
47μF 63V
47μF 63V
Not required
47μF 63V
Not required
Not required
Not required
Not required
C4
10μF 25V
10μF 25V
10μF 25V
10μF 25V
10μF 25V
10μF 25V
10μF 25V
10μF 25V
L1
L2
MPS 18R333C
33μH 2A
MPS 18R333C
33μH 2A
MPS 18R333C
33μH 2A
MPS 18R333C
33μH 2A
MPS 18R104C
100μH 1.2A
MPS 18R104C
100μH 1.2A
MPS 18R104C
100μH 1.2A
MPS 18R104C
100μH 1.2A
L3
4.7μH
10μH
MPS 49330C
33μH 2.5A
MPS 18R333C
33μH 2.00A
4.7μH
10μH
MPS 49330C
33μH 2.5A
MPS 18R333C
33μH 2.00A
C1, C2 & C4 : Electrolytic capacitors
C3 : Polyester or ceramic capacitor
EMC Spectra red limit line is EN 55022 curve B Quasi-peak average limit.
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