Removal of Soldered Converters from Printed Circuit Boards
Should removal of the converter from its soldered connection be needed,
thoroughly de-solder the pins using solder wicks or de-soldering tools. At no
time should any prying or leverage be used to remove converters that have not
been properly de-soldered fi rst.
Input Source Impedance
These 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.
I/O Filtering, Input Ripple Current, and Output Noise
All models in this Series are tested/specifi ed for input ripple current (also called
input refl ected ripple current) and output noise using the circuits and layout
shown in Figures 2 and 3. External input capacitors (C
IN in Figure 2) serve
primarily as energy-storage elements.
They 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 impedance can affect system stability. In Figure 2, C
BUS and
L
BUS simulate a typical dc voltage bus. Your specifi c system confi guration may
necessitate additional considerations.
In critical applications, output ripple and noise (also referred to as periodic and
random deviations or PARD) may be reduced by adding fi lter elements such
as multiple external capacitors. Be sure to calculate component temperature
rise from refl ected AC current dissipated inside capacitor ESR.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 be taken 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.
Figure 2. Measuring Input Ripple Current
CINVIN CBUS
LBUS
See specs for component values.
1
3
+VIN
–VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
TECHNICAL NOTES
Figure 3. Measuring Output Ripple/Noise (PARD)
C1
C1 = 1μF
C2 = 10μF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
7
8
4
5
SCOPE
+VOUT
–VOUT
+SENSE
–SENSE
Start-Up Threshold and Undervoltage Shutdown
Under normal start-up conditions, these converters will not begin to regulate
properly until the ramping input voltage exceeds the Start-Up Threshold. Once
operating, devices will turn off when the applied voltage drops below the Und-
ervoltage Shutdown point. Devices will remain off as long as the undervoltage
condition continues. Units will automatically re-start when the applied voltage
is brought back above the Start-Up Threshold. The hysteresis built into this
function avoids an indeterminate on/off condition at a single input voltage. See
Performance/Functional Specifi cations table for actual limits.
Start-Up Time
The VIN to VOUT Start-Up Time is the interval between the point at which a
ramping input voltage crosses the Start-Up Threshold voltage and the point at
which the fully loaded output voltage enters and remains within its specifi ed
regulation band. Actual measured times will vary with input source imped-
ance, external input capacitance, and the slew rate and fi nal value of the input
voltage as it appears to the converter. The On/Off to V
OUT start-up time assumes
that the converter is turned off via the Remote On/Off Control with the nominal
input voltage already applied.
On/Off Control
The primary-side, Remote On/Off Control function can be specifi ed to operate
with either positive or negative polarity. Positive-polarity devices ("P" suffi x)
are enabled when the on/off pin is left open or is pulled high. Positive-polarity
devices are disabled when the on/off pin is pulled low (with respect to –Input).
Negative-polarity devices are off when the on/off pin is high and on when the
on/off pin is pulled low. See Figure 4.
Dynamic control of the remote on/off function is best accomplished with a me-
chanical relay or an open-collector/open-drain drive circuit (optically isolated if
appropriate). The drive circuit should be able to sink appropriate current (see
Performance Specifi cations) when activated and withstand appropriate voltage
when deactivated.
HPQ-3.3/50-D48 Series
Isolated High Power Quarter Brick DC-DC Converters
MDC_HPQ-3.3/50-D48 Series.B01 Page 9 of 11
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