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 boards that have not

been properly de-soldered first.

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/specified for input ripple current (also called

input reflected ripple current) and output noise using the circuits and layout

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

may necessitate additional considerations.

In critical applications, output ripple/noise (also referred to as periodic and ran-

dom deviations or PARD) can be reduced below specified limits using filtering

techniques, the simplest of which is the installation of additional external out-

put capacitors. Output capacitors function as true filter elements and should be

selected for bulk capacitance, low ESR, and appropriate frequency response.

In Figure 3, the two copper strips simulate real-world pcb impedances between

the power supply and its load. Scope measurements should be made using

BNC connectors or the probe ground should be less than ½ inch and soldered

directly to the fixture.

All external capacitors should have appropriate voltage ratings and be located

as close to the converter as possible. Temperature variations for all relevant

Figure 2. Measuring Input Ripple Current

See specs for component values.

3

1

+INPUT

–INPUT

CURRENT

PROBE

TO

OSCILLOSCOPE

+

–

Technical Notes

ductor capacitors (www.sanyo.com) can be especially effective for further

reduction of ripple/noise.

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 3. Measuring Output Ripple/Noise (PARD)

C1

C1 = 1μF CERAMIC

C2 = 10μF TANTALUM

LOAD 2-3 INCHES (51-76mm) FROM MODULE

C2

7

8

COPPER STRIP

4

5

COPPER STRIP

SCOPE

+OUTPUT

–OUTPUT

+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 Specifications table for actual limits.

Start-Up Time

ing input voltage crosses the Start-Up Threshold voltage and the point at which

the fully loaded output voltage enters and remains within its specified accuracy

band. Actual measured times will vary with input source impedance, external

input capacitance, and the slew rate and final value of the input voltage as it

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 specified to operate

with either positive or negative polarity. Positive-polarity devices ("P" suffix)

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 Specifications) when activated and withstand appropriate voltage

when deactivated.

HPQ Series

Isolated High Power Quarter Brick DC/DC Converters

MDC_HPQ Series.A07 Page 6 of 10

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