Wall Industries, Inc.

Rev D

MPQ SERIES

Up to 125 Watts, Quarter-Brick DC/DC Converters

02/15/2013

Wall Industries, Inc. • 5 Watson Brook Road, Exeter, NH 03833 • Tel: 603-778-2300 • Toll Free: 888-597-9255 • Fax 603-778-9797

website: www.wallindustries.com • e-mail: sales@wallindustries.com

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DESIGN CONSIDERATIONS

Under Voltage Lock Out (UVLO)

The converter output is disabled until the input voltage exceeds the UVLO turn-on limit. The converter will remain ON until the input voltage falls

below the UVLO turn-off limit.

Over Current Protection

The converter is protected from short circuit and over current conditions. Upon sensing an over current, the output will begin to drop (or ‘foldback’)

limiting the output power. Further increasing the output current will cause the converter to shut off and then restart (or ‘hiccup’) until the over

current condition is removed. Shorting the output will cause the converter to immediately enter the ‘hiccup’ mode.

Over Temperature Protection

The converter is protected from over temperature conditions. Upon exceeding this temperature, the converter will shut down. The converter will

automatically recover once the over temperature condition is removed.

Input Filter

No additional input capacitor is needed for the power supply to operate. However, due to the low voltage, high input current nature of the power

supply; it is highly recommended that a minimum 100µF/50 V electrolytic type input bulk capacitor be added to reduce input ripple voltage and

current. Refer to Photos 1 and 2 for an example. For an even further reduction of input ripple, an inductor may be placed between the source and

the previously mentioned capacitor. Additionally, a 1-10µF ceramic capacitor may be added in front of the inductor to form pi-filter. No inductor

should be placed between the capacitor and the input to the converter.

Output Filter

No additional output capacitor is needed for the power supply to operate. However, to reduce the ripple and noise on the output, additional

capacitance may be added. Usually, a ceramic capacitor between 1 and 100µF works best for reducing ripple and spike noise. Also, capacitance in

the form of a low-ESR, surge robust tantalum capacitor (ie: Kemet T495 Series) may also be placed across the output in order reduce ripple, and

improve the transient peak-to-peak voltage deviation. Due to the low-ESR nature of the output of the power supply, adding typical aluminum

electrolytic capacitors to the output will not help much in reducing ripple or transient deviations, unless the load is some distance from the power

supply output. Then, these capacitors should be placed at the load.

Remote Sense

To improve regulation at the load, route the connections from the -Sense and the +Sense pins to the –Vout and +Vout connections at the load. This

will force the converter to regulate the voltage at the load and not at the pins of the converter. If it is not desired to use the Remotes Sense feature,

the –Sense and +Sense pins should be shorted to the -Vout and +Vout pins respectively. However, no damage to the converter will occur if the

Sense pins are left open.

Fusing

It is required that the input to the converter be supplied with a maximum 10 A, 250 V rated fuse UL Listed or R/C fuse.

Safety

The MPQ series is designed to meet EN60950 Safety of Information Technology Equipment. The isolation provided by the MPQ series is a basic

insulation in accordance with EN60950. SELV output reliability is maintained only if the input to the converter is a SELV source. To maintain SELV

reliability, if either +Vin or –Vin is connected to chassis, either +Vout or –Vout must also be connected to chassis. Otherwise, both the input and the

output must not be connected to chassis.

PCB Layout Considerations

Due to the basic isolation provided by the converter, caution must be observed in routing traces more than 2mm inward of any input or output pins

on the top layer of the PCB board underneath the converter. Also, due to noise coupling and isolation requirements, no power or ground planes or

any signal traces should be routed on the top layer of the PCB underneath the converter. Due to common noise coupling, input or output power

and ground planes should not be poured across the input to output on any layers underneath the converter. Instead, it is best to provide separate

input and output power and ground traces on the bottom or an inner layer with a minimum of 1mm separation between traces on the same layer.

Lastly, as the case/heatsink is floating metal, caution must also be observed to provide appropriate spacing (minimum 1.4mm for Pollution degree 2

Material Group IIIa + IIIb) around the case/heatsink or risk reducing the input to output spacing and violating basic insulation requirements.