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, i.e. IEC/EN/UL 60950-1.
Input Under-Voltage Shutdown and Start-Up Threshold
Under normal start-up conditions, converters will not begin to regulate properly
until the ramping-up input voltage exceeds and remains at the Start-Up
Threshold Voltage (see Specifi cations). 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 opera-
tion at a single input voltage.
Users should be aware however of input sources near the Under-Voltage
Shutdown whose voltage decays as input current is consumed (such as poorly
regulated 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.
Start-Up Time
Assuming that the output current is set at the rated maximum, the Vin to Vout
Start-Up Time (see Specifi cations) is the time interval between the point when
the ramping input voltage crosses the Start-Up Threshold and the fully loaded
regulated output voltage enters and remains within its specifi ed regulation
band. Actual measured times will vary with input source impedance, external
input capacitance, input voltage slew rate and fi nal value of the input voltage
as it appears at the converter.
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.
The On/Off Remote Control interval from On command to Vout regulated
assumes that the converter already has its input voltage stabilized above the
Start-Up Threshold before the On command. The interval is measured from the
On command until the output enters and remains within its specifi ed accuracy
band. The specifi cation assumes that the output is fully loaded at maximum
rated current. Similar conditions apply to the On to Vout regulated specifi cation
such as external load capacitance and soft start circuitry.
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
TECHNICAL NOTES
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 com-
ponents, circuits and layout as shown in the fi gures below. The Cbus and Lbus
components simulate a typical DC voltage bus. Please note that the values of
Cin, Lbus and Cbus may vary according to the specifi c converter model.
Minimum Output Loading Requirements
All models regulate within specifi cation and are stable under no load to full
load conditions. Operation under no load might however slightly increase
output ripple and noise.
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
temperature hysteresis to prevent rapid on/off cycling.
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
+INPUT
-INPUT
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
Figure 2: Measuring Input Ripple Current
OKX T/10 & T/16-W5 Series
Adjustable DOSA 10/16-Amp SIP DC/DC Converters
MDC_OKX_T10T16-W5 Series.A06 Page 11 of 13
www.murata-ps.com/support
