5V Step-Up Voltage Regulator U3V9F5

The U3V9Fx family of boost (step-up) voltage regulators generate higher output voltages from input voltages as low as 2.6 V. They are switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) and have typical efficiencies between 70% and 95%.

The regulators actively limit the instantaneous input currents to 2.2 A when boosting, and input currents up to around 900 mA can typically be maintained for many minutes without triggering thermal shutdown, though the actual performance depends on the input and output voltages as well as external factors such as ambient temperature and airflow. For boost regulators, the output current equals the input current times the efficiency divided by the boost ratio of VOUT to VIN, so the more you are boosting, the lower the maximum output current will be (see the maximum continuous output current section below for performance graphs).

These regulators have several built-in protections, including cycle-by-cycle input current limiting and over-temperature shutdown.

Warning: This boost regulator uses the typical topology that connects the input to the output through an inductor and diode, with nothing to completely break that current path. Therefore, the input voltage will go through to the output if it exceeds the set output voltage, and exposure to short circuits or other excessive loads will damage the regulator. This regulator also does not have built-in protection against reverse voltage, but reverse-voltage protection modules are available for adding that functionality.

This family includes six versions with fixed output voltages ranging from 5 V to 24 V:

• U3V9F5: Fixed 5V output
• U3V9F9: Fixed 9V output
• U3V9F12: Fixed 12V output
• U3V9F15: Fixed 15V output
• U3V9F18: Fixed 18V output
• U3V9F24: Fixed 24V output

The different versions of the board all look very similar, so you might consider adding your own markings or other distinguishing features if you have multiple versions that you need to be able to tell apart.

Pololu manufacture these boards in-house at Pololu's Las Vegas facility, so Pololu can make these regulators with customized components to better meet the needs of your project, such as by customizing the output voltage between 4.5 V and 28 V. If you are interested in customization, please contact us.

Details for item #5581

5V Step-Up Voltage Regulator U3V9F5, top view.

Features and specifications

• Output voltage: 5 V with 4% accuracy
• Input voltage: 2.6 V to 20 V (Note: input voltages above 5 V will pass through to the output)
• Typical efficiency of 70% to 90%, depending on input voltage, output voltage, and load (see the efficiency graph below)
• Switching frequency: ~1.6 MHz under heavy loads
• Power-save mode that increases light load efficiency by reducing switching frequency
• Typical no-load quiescent currents under 0.2 mA (see the quiescent current graph below)
• 2.2 A switch current limit
• Typical continuous input currents up to around 900 mA (see the maximum continuous output current graph below)
• Tolerates input voltage above output set voltage (output will track input, see the connections section for details)
• Integrated protections:
  • Over-temperature shutdown
  • Soft-start feature limits inrush current and gradually ramps output voltage
  • Cycle-by-cycle peak input current limiting
• Compact size: 0.54" × 0.34" × 0.11" (13.6 × 8.6 × 2.8 mm)
• Weight: 0.4 g

Connections

The input voltage, VIN, must be at least 2.6 V and should not exceed 20 V. Please note that if VIN is higher than VOUT, the higher input voltage will show up on the output, which could be dangerous for your connected load if it cannot tolerate that higher voltage. The regulator itself should generally be able to tolerate such pass-through voltages as long as they do not exceed 20 V and the load is not trying to draw currents through the regulator that are beyond what the regulator can withstand.

VOUT is the regulated output voltage. The regulator’s soft-start feature gradually ramps up the VOUT voltage on start-up to limit in-rush current draw. The U3V9Fx regulators do not have short-circuit protection, so Pololu could be damaged if exposed to output shorts or excessive loads, and they do not have reverse-voltage protection. Reverse-voltage protection modules are available separately that can be inserted between the power supply and these regulators to protect them from accidental reversal of input power polarity.

The connections are labeled on the back side of the PCB and are arranged with a 0.1" spacing along the edge 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" headers directly to the board. Note: header pins are not included with this product, but 1×3 straight male headers and 1×3 right-angle male headers are available separately.

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.

Maximum continuous output current

The maximum achievable output current is approximately proportional to the ratio of the input voltage to the output voltage. Additionally, the maximum output current can depend on other factors, including the ambient temperature and air flow. The graph below shows the typical maximum continuous output currents these regulators can deliver at room temperature with no forced airflow or heat sinking.

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.

LC Voltage Spikes

When connecting voltage to electronic circuits, the initial rush of current can cause damaging voltage spikes that are much higher than the input voltage. In Pololu's tests with this family of regulator connected with typical power leads (~30" test clips), Pololu found that input voltages up to 13 V did not generally cause spikes high enough to damage the regulator itself, but even lower input voltages did cause spikes that could still be problematic for boost regulators operating with the input voltage close to the set output voltage, since input voltages above the set output voltage will propagate to the output and could damage circuits being powered by the regulator. 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.

More information about LC spikes can be found in Pololu's application note, Understanding Destructive LC Voltage Spikes.

Dimensions

General specifications

Identifying markings

Notes:

1

The input voltage is passed through to the output of the regulator if VIN exceeds VOUT.

2

Instantaneous. This is the rating for the switch, and the regulator actively limits input current to this when boosting. Sustainable input current is closer to 900 mA and depends on input and output voltage and external conditions like ambient temperature and airflow. See the graph under the description tab for more information.

3

See the quiescent current graph under the description tab for more information.

File downloads

• Dimension diagram for the Step-Up Voltage Regulator U3V9Fx (299k pdf)

• 3D model of the Step-Up Voltage Regulator U3V9Fx (3MB step)

• Drill guide for the Step-Up Voltage Regulator U3V9Fx (13k dxf)

  This DXF drawing shows the locations of all of the board’s holes.