Q:

What is the PWB footprint for the RO modules?

A:

RO's modules are generally smaller than our competitor's modules. The basic, recommended PWB footprints for our modules are shown in Application Note 19, Hole Dimensions and Socket Information. In addition, the outline drawings included in the product data sheets provide a good source of information for creating custom PWB footprints.
 

Q:

How much heatsinking do I need for the RO converters?

A:

The amount of heatsinking required is determined by the environment that the module is placed in, the heat produced in the module, and the maximum desired baseplate temperature. Because RO's modules are highly efficient the required heatsinking is minimal. It may even be possible to operate the modules without any additional heatsinking. The thermal performance curves in the data sheets were designed so that you can quickly determine the amount of heatsinking required for your application. A more in-depth discussion of thermal design with the RO modules is available in Application Note 10, Thermal Considerations.

Q:

Why do I see 1V spikes on the output of the module?

A:

These spikes do not really occur on the output, rather they are mostly the result of noise pickup and measurement error in the test setup used. A common source of noise pickup is the loop created by the ground clip on most standard scope probes. Application Note 8, Noise and Ripple Measurement discusses how to properly measure the output noise and ripple.

Q:

Can RO modules be used with no additional components?

A:

Yes, in some applications they can. However, bypass capacitors are often required to reduce system noise and achieve proper module performance. For basic systems, we recommend that pads and traces for the components shown in Figure 1 be included in the initial PWB layout. The design team can then either optimize them for performance or, if performance is good, eliminate them for cost reduction.

Figure 1 Basic Connections For a Single Module System.

Q:

Paralleling De-coupling Modules (PDMs) are great when redundancy is required, but can the RO modules be paralleled without PDMs?

A:

Q:

What is the recommended solder process for the modules?

A:

The recommended solder process is a wave solder process with the solder wave at 260°C. Each pin should be in the wave for 5 seconds and the big pins should enter the wave last. Because the modules have a high thermal mass, the preheat cycle must be lengthened in order for proper solder wetting of the pins to occur.

Q:

Why do the modules sometimes seem to current limit to early?

A:

Noise on the Parallel Pin, the Input Pins, or the Output Pins can cause premature current limit in the modules. Application Note 13 Paralleling-Current Sharing, Hot Plug-in, and N+M Redundancy and Application Note 18 Board Layout Considerations and Recommendations provide some preventative and corrective measures that can be taken to reduce the noise. Adding the proper bypass caps to these pins will usually solve the problem.
 

Q:

Why does the output noise increase when I connect the output return lines of the triple output module together?

A:

As with most multiple output power supplies, common mode noise can be injected from one output into another causing increased noise. Adding a small, common mode choke of about 25µH per leg to each auxiliary output, before the common ground connection, will prevent this from occurring.
 

Q:

How does the output good signal function?

A:

The output good signal provides an active low output whenever the sensed output voltage is within ±10% of the set output voltage; otherwise it appears as an open collector (Vmax = 40V). The signal is referenced to -SENSE (See Figure 2) and is capable of sinking 15mA typical (8mA minimum). The output low voltage (saturation voltage) is 0.5V or less @ Isink = 1.6mA. The output good signal changes its state in the range Vsense = ±9% to ±11% of Vsetpoint.

Figure 2 Equivalent circuit of the Output Good Signal
 

Q:

How do I use the ON/ OFF pin?

A:

The ON/ OFF pin may be used to turn the module off and on remotely using a low level signal. When ON/ OFF is pulled low (< 1V @ 4mA, referenced to -Vin), the module is turned off. All that is required to interface the ON/ OFF signal to other circuits is a few external components as shown in Figure 3. Additional ways to use the ON/OFF pin are shown in Application Note 4, Logic On-Off.

Figure 3 Logic on/off circuit with small signal transistor. A logic high signal disables the converter.