DC/DC Converter Array Project

In this project, we will highlight a DC-DC converter array, which includes multiple power regulators providing different voltage outputs and an interface for an external controller, such as a microcontroller board. The design allows the user to access multiple high-power voltage outputs with sustained current with several Amps of current per output. Finally, power is provided by a barrel jack connector at 9 V DC, so it can be powered with a small wall wart.

This design is based around an array of TDK FS140x DC-DC converter modules. These modules are non-isolated modules that can be controlled externally. They have the following features:

• Control with I2C interface
• PGOOD monitoring
• EN toggling with external controller or switch
• Internal feedback loop compensation
• Multiple voltage output options based on part number
• No external inductor required

DC-DC Converter Array Design

Schematics and Circuits

The main regulator circuit for each of the FS140x modules is shown below. The particular circuit shown here is an initial design based on TDK’s reference designs for the FS1406 DC-DC converter module. This circuit is extensible across the FS140x product line.

The BOM for this design includes 4x FS1406, 1x FS1404, and 1x FS1403. Note that this is a part number family; the voltage output from each of these modules is different based on a specific part number within each family.

These modules have fixed voltage outputs, which is delineated by manufacturer part number. The designer can change the available voltage output by a simple BOM swap. For example, if you look in the FS1406 datasheet on page 5, you will see a series of part numbers with the FS1406, each with fixed output voltage. If a different output voltage is required in this design, just swap out one module for an alternative part number within the same part number family.

The design also includes control over power-up and enable of using a pair of switches, as well as a DIP switch array. These switches are simple slide switches as shown below. The SLG7TD43741 also acts as a power-up sequencer. On initial power-up the sequencer will toggle the EN pins on the DC-DC converter modules, and will then output a HIGH signal to the LED indicators. This will turn on the LEDs in order to indicate which DC-DC converters have received an enable signal.

Other components in the design include:

• 3.3 V regulator for the powering the sequencer
• Headers for accessing PGOOD monitoring and EN monitoring
• A 2-pin header for an I2C connection

Placement and Routing

Initially, the design contained only pin headers to access power outputs from each of the converter modules in the array. The initial placement with I/O access, barrel connector access, and pin header placement for the modules is shown below. This was initially done in a quarter-brick format.

Given the current output capabilities from this module, it was decided to place screw terminal blocks on the power outputs. This allows more rugged connections to the output terminals with a screw rather than a flying lead connection to a pin header. Screw terminal blocks are also available as an option to power up the PVIN net.

Typically in designs like this, where we have a wide input range on the power stage and stepped down output, we are using a switching regulator that requires careful placement and routing of the inductors to minimize noise from the switching node. However, because we are using integrated modules for the DC-DC converters in the array, the modules include the required inductance in a very compact package and we do not need to worry as much about this point regarding routing. This is one of the big advantages of using modules as opposed to designing with discrete components.

Instead, we only need to worry about placement of capacitors for DC stability and to filter any switching noise on the output. We can see this from the above schematic view, which was built following TDK’s reference designs for FS140x modules.

Because the power output can be moderately high, we also route each section using large copper fills. The power input routing to all of the DC-DC converter modules is routed on a dedicated layer (L3) using a large piece of copper pour. This also allows easy connections for capacitors on the input power rail. The outputs are routed to the screw terminal blocks as shown below; the other three outputs mirror this along the bottom edge of the board.

Ground is placed using two nets, PGND and a system GND. It’s important to note that this is a common practice with DC-DC converters and it is not implemented with the intent to isolate two different ground regions. Instead, this is used to control the return paths involved in the design; the two ground regions are set to the same potential internally in the converter modules, thus we use routed PGND lines on L1 and a continuous ground on L2.

The finalized design is shown in the 3D view below.

What Else Can You Do With This Design?

Because the design is extensible across a part number family, users can modify the design to produce new variants very quickly without needing to make changes to the PCB layout. If you were to make this into product that would be sold on the market, there are a few simple changes that can enhance the design:

• Add additional mounting holes to make the board standalone or integrated into a custom enclosure
• Swap the terminal blocks with pogo pins or plug-in connectors that could be exposed through the top side of an enclosure
• If the board will not use an enclosure, space out the terminal blocks a bit to show silkscreen markings for power levels
• Consider adding a small fan for airflow if the design will be run at high power

To download the project files for this design, click here.

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