Datasheet
Input Fusing
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 Input Filtering
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.
For best performance, we recommend installing a low-ESR capacitor
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.
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.
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 specifi cations.
Input Ripple Current and Output Noise
All models in this converter series are tested and specifi ed for input refl ected
ripple current and output noise using designated external input/output compo-
nents, circuits and layout as shown in the following fi gures. 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 specifi c converter model.
TECHNICAL NOTES
C
IN
V
IN
C
BUS
L
BUS
C
IN
= 2 x 100μF, ESR < 700mΩ @ 100kHz
C
BUS
= 1000μF, ESR < 100mΩ @ 100kHz
L
BUS
= 1μH
+VIN
-VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
Figure 3 Measuring Input Ripple Current
C1
C1 = 1μF
C2 = 10μF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
-VOUT
Figure 4. Measuring Output Ripple and Noise (PARD)
MDC_OKI-78SR-W36.C03 Page 11 of 12
OKI-78SR Series
Fixed Output 1.5 Amp SIP DC/DC Converters
www.murata-ps.com/support