HPQ-12-D48_11 Datasheet, PDF (9/14 Pages) Murata Manufacturing Co., Ltd. – Isolated 300-Watt Quarter Brick DC/DC Converters

HPQ-12/25-D48 Series
Isolated 300-Watt Quarter Brick DC/DC Converters
APPLICATION NOTES
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.
Input Reverse-Polarity Protection
If the input voltage polarity is reversed, an internal diode will become forward
biased and likely draw excessive current from the power source. If this source
is not current-limited or the circuit appropriately fused, it could cause perma-
nent damage to the converter.
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.
Users should be aware however of input sources near the Under-Voltage Shut-
down whose voltage decays as input current is consumed (such as capacitor
inputs), the converter shuts off and then restarts as the external capacitor re-
charges. 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 Delay
Assuming that the output current is set at the rated maximum, the Vin to Vout Start-
Up Delay (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 volt-
age slew rate and final value of the input voltage as it appears at the converter.
These converters include a soft start circuit to moderate the duty cycle of the
PWM controller at power up, thereby limiting the input inrush current.
The On/Off Remote Control interval from inception 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 specified regulation band. The specification
assumes that the output is fully loaded at maximum rated current.
Input Source Impedance
These converters will operate to specifications without external components,
assuming that the source voltage has very low impedance and reasonable in-
put voltage regulation. Since real-world voltage sources have finite impedance,
performance is improved by adding external filter components. Sometimes only
a small ceramic capacitor is sufficient. Since it is difficult to totally characterize
all applications, some experimentation may be needed. Note that external input
capacitors must accept high speed switching currents.
Because of the switching nature of DC/DC converters, the input of these
converters must be driven from a source with both low AC impedance and
adequate DC input regulation. Performance will degrade with increasing input
inductance. Excessive input inductance may inhibit operation. The DC input
regulation specifies that the input voltage, once operating, must never degrade
below the Shut-Down Threshold under all load conditions. Be sure to use
adequate trace sizes and mount components close to the converter.
I/O Filtering, 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. External input capaci-
tors (CIN in the figure) serve primarily as energy storage elements, minimizing
line voltage variations caused by transient IR drops in the input conductors.
Users should select input capacitors for bulk capacitance (at appropriate
frequencies), low ESR and high RMS ripple current ratings. In the figure below,
the CBUS and LBUS components simulate a typical DC voltage bus. Your specific
system configuration may require additional considerations. Please note that the
values of CIN, LBUS and CBUS may vary according to the specific converter model.
TO
OSCILLOSCOPE
+
VIN ^–
+
–
LBUS
CBUS
CURRENT
PROBE
CIN
+INPUT
−INPUT
CIN = 33μF, ESR < 200mΩ @ 100kHz
CBUS = 220μF, 100V
LBUS = 4.7μH
Figure 2. Measuring Input Ripple Current
In critical applications, output ripple and noise (also referred to as periodic and
random deviations or PARD) may be reduced by adding filter elements such
as multiple external capacitors. Be sure to calculate component temperature
rise from reflected AC current dissipated inside capacitor ESR. In figure 3, the
two copper strips simulate real-world printed circuit impedances 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 connec-
tors or the probe ground should not exceed one half inch and soldered directly
to the fixture.
Floating Outputs
Since these are isolated DC/DC converters, their outputs are “floating” with
respect to their input. The essential feature of such isolation is ideal ZERO
CURRENT FLOW between input and output. Real-world converters however do
exhibit tiny leakage currents between input and output (see Specifications).
These leakages consist of both an AC stray capacitance coupling component
and a DC leakage resistance. When using the isolation feature, do not allow
the isolation voltage to exceed specifications. Otherwise the converter may
be damaged. Designers will normally use the negative output (-Output) as
the ground return of the load circuit. You can however use the positive output
(+Output) as the ground return to effectively reverse the output polarity.
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21 Feb 2011 MDC_HPQ-12/25-D48 Series.A07 Page 9 of 14