Overview

These buck (step-down) voltage regulators generate lower output voltages from input voltages as high as 42V. They are switching regulators (also called switched-mode power supplies (SMPS) or DC-to-DC converters) and have a typical efficiency between 80% to 90%, which is much more efficient than linear voltage regulators, especially when the difference between the input and output voltage is large. This regulator is available with a fixed 3.3V output at 600mA. A 300mA maximum output current version is also available (D24V6Fx).

The regulator has short-circuit protection, and thermal shutdown prevents damage from overheating. The board does not have reverse-voltage protection.

Features

• input voltage: 5V to 42V
• fixed 3.3 V output with 4% accuracy
• maximum output current: 600 mA (D24V3Fx)
• 550 kHz switching frequency
• 2 mA typical no-load quiescent current (20 μA typical quiescent current with SHDN = LOW)
• integrated over-temperature and over-current shutoff
• small size: 0.5" × 0.4" × 0.1" (13 × 10 × 3mm)

Using the Regulator

Connections

The buck regulator has four connections: shutdown (SHDN), input voltage (VIN), ground (GND), and output voltage (VOUT).

The SHDN pin can be driven low (under 0.3V) to turn off the output and put the board into a low-power state that typically draws 20μA. The SHDN pin can be driven high (above 2.3V) to enable the board, or it can be connected to VIN or left disconnected if you want to leave the board permanently enabled.

The input voltage, VIN, should be at least a few volts above VOUT, and you must ensure that noise on your input does not exceed the 42V maximum. Additionally, please be wary of destructive LC spikes (see below for more information).

The output voltage, VOUT, is fixed.

The four connections are labeled on the back side of the PCB, and they 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 directly to the board or solder in either the 4×1 straight male header strip or the 4×1 right-angle male header strip that is included.

Typical Efficiency and Output Current

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. As shown in the graphs above, this switching regulator typically has an efficiency of 80 to 90%.

Note that the above graphs apply to both the 300mA and 600mA versions, which is why the x axis extends to 600 mA. You should not expect to get more than 300mA from the 300mA versions (D24V3Fx).

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 (42V), the regulator can be destroyed. In our tests with typical power leads (~30" test clips), input voltages above 20V caused spikes over 42V. If you are connecting more than 20 V or your power leads or supply has high inductance, we recommend soldering a 33μF or larger electrolytic capacitor close to the regulator between VIN and GND. The capacitor should be rated for at least 50V.

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