This step-up/step-down voltage regulator consists of an isolated DC-to-DC power module between an input step-down (buck) regulator and an output step-up (boost) regulator. This enables up to 100 mA at 12 V out or 300 mA at 5 V out from a wide 5.5 V to 36 V input.

This step-up/step-down voltage regulator consists of a Texas Instruments UCC33420RAQR isolated DC-to-DC power module between a 5 V buck regulator on the input side and a 12 V boost regulator on the output side, enabling up to 100 mA at 12V out from a wide 5.5 V to 36 V input. The 5 V output of the UCC33420 that powers the boost regulator is also brought out, which can provide up to 300 mA continuous when there is no 12 V current draw (using the 5 V output will reduce available current from the 12 V output). Unlike non-isolated regulators, the output ground (GNDO) is effectively independent of the input side (GNDI), which can be useful for preventing ground loops and avoiding ground currents that can cause unpredictable system behavior or even lead to damage to potentially expensive components.

Here are some of the regulator’s key features:

Input voltage: 5.5 V to 36 V (can operate down to 4.6 V with reduced output current capabilities)
Outputs:

12 V (with 4% accuracy), up to 100 mA continuous (when 5V output current is zero)
5 V (with 4% accuracy), up to 300 mA continuous (when 12V output current is zero)

Galvanic isolation between input and output using the Texas Instruments UCC33420, which has the following isolation ratings:

3000 VRMS basic isolation rating
820 VRMS maximum working isolation voltage
See the UCC33420 datasheet for more information

Typical no-load quiescent current: 1 mA to 10 mA (see the quiescent current graph below)
Typical efficiency: 40% to 50%, depending on input voltage and load (see efficiency graph below)
Input (buck) switching frequency: ~1.1 MHz under heavy loads
Output (boost) switching frequency: ~1.6 MHz under heavy loads
Input and output switching frequencies decrease at low currents to improve light-load efficiency
Over-temperature protection
Size: 0.4″ × 1.3″ with breadboard-compatible, 0.1″-pitch through holes

Using the module

The connections are labeled on the back side of the PCB and are arranged with a 0.1″ spacing along the edges of the board for compatibility with solderless breadboards, connectors, and other prototyping arrangements that use a 0.1″ grid. You can solder wires or 0.1″ header pins directly to the board. Note: header pins are not included with this product, but straight and right-angle male headers are available separately.

We manufacture these boards in-house at our Las Vegas facility, so we can make these regulators with customized components to better meet the needs of your project, such as by customizing the output voltage between 5.5 V and 28 V (though please note that the available current decreases significantly at higher output voltages). If you are interested in customization, please contact us.

Typical efficiency

The efficiency of a voltage regulator, defined as (Power out)/(Power in), is an important measure of its performance, especially when battery life or heat are concerns. The graph below shows the efficiencies of the VOUT (12 V) output at different input voltages as a function of output current:

Please note that as this module consists of three chained regulators and includes isolated power transfer, the efficiency is below 50%, which is much lower than our non-isolated switching voltage regulators. The efficiency of the 5 V output is slightly higher since that does not go through the final boost stage, but it is still below 60%.

Maximum continuous output current

The graph below shows the typical VOUT (12 V) maximum continuous output current this regulator can deliver at room temperature with no forced airflow or heat sinking.

For the 5 V output, the maximum continuous output current is 300 mA. Please note that these two outputs are NOT independent, since both ultimately come from the UCC33420, which is the limiting factor. When drawing 100 mA from VOUT, no additional current is available from the 5 V output, and when drawing 300 mA from the 5 V output, no additional current is available from VOUT.

During normal operation, this product can get hot enough to burn you. Take care when handling this product or other components connected to it.

Quiescent current

The quiescent current is the current the regulator uses just to power itself, and the graph below shows this for the different regulator versions as a function of the input voltage.

Reduced output current for input voltages under 5.5 V

The recommended minimum input voltage for this regulator is 5.5 V, but it can operate down to around 4.6 V with reduced VOUT (12 V) output current capabilities as shown in the graph below:

Isolation rating and board creepage considerations

The UCC33420 provides basic isolation with a manufacturer-rated working voltage of 820 VRMS. The IC package has a clearance and creepage of >4.1 mm, and our PCB has a routed slot under the IC that increases the PCB creepage to 4.9 mm. A rough rule of thumb is that uncontaminated FR4 PC Bs should have roughly 1 mm of creepage per 100 VRMS of isolation. Please note that our regulator module is not certified to any particular safety standard.

LC voltage spikes

When connecting voltage to electronic circuits, the initial rush of current can cause voltage spikes that are much higher than the input voltage. If these spikes exceed the regulator’s maximum voltage (36 V), the regulator can be destroyed. In our tests with typical power leads (~30″ test clips), we observed spikes approaching 36 V at input voltages approaching 20 V. Power supplies or leads with high inductance will make these spikes worse. An electrolytic capacitor (33 μF is a good starting point) can be added close to the regulator between VIN and GND to help suppress these spikes.

Specifications