Step-Down DC-DC Converter

The Buck Converter is designed to perform critical functions such as reducing the input voltage to the output and minimizing voltage ripple.

These critical functions are as follows:

- Reducing the 3.5V to 28V input voltage to a fixed 3.3V output voltage.

- Performing high-efficiency DC-DC conversion.

- Minimizing current and voltage ripple at the input and output voltages.

Design Parameters

The TPS54331 was selected as the core converter IC due to its integrated MOSFET's low RDS(on) resistance, which ensures high efficiency and cost-effectiveness. Additionally, its 1-μA shutdown supply current makes it suitable for battery-powered applications. The current mode control with internal slope compensation simplifies external compensation calculations, reduces component count, and allows for the use of ceramic output capacitors. A resistor divider sets the hysteresis for input undervoltage lockout. An overvoltage transient protection circuit limits voltage overshoot during startup and transient conditions. The device and load are protected from overloads by a cycle-by-cycle current-limit scheme, frequency foldback, and thermal shutdown.

The circuit operates over a wide voltage range of 3.5-28V, making it versatile for various applications. The ENABLE pin on the IC provides the necessary voltage for startup. A voltage divider sets a minimum input voltage of 5V. Decoupling capacitors at the inputs and outputs eliminate voltage fluctuations, ensuring pure DC power delivery to the circuit components.

The IC features a Programmable Slow Start, used with the SS pin, offering benefits such as input source protection, inrush current prevention, output overshoot prevention, and control loop stability. A 10nF capacitor achieves a 4ms time.

The IC operates with a fixed 570kHz switching frequency.

To prevent subharmonic oscillations when the device functions at duty cycles greater than 50%, the TPS54331 includes an integrated slope compensation. This is an additional ramp added to the switch-current signal.

The VSENSE pin serves as the inverting node of the transconductance (gm) error amplifier, which compares the VSENSE voltage to the internal reference voltage at the error amplifier's input.

The COMP pin is both the error-amplifier output and the input to the PWM comparator. Frequency compensation components are connected to this pin.

In current mode control, the COMP pin voltage is used to switch off the high-side MOSFET on a cycle-by-cycle basis. Each cycle compares the switch current with the COMP pin voltage. When the peak inductor current matches the COMP pin voltage, the high-side switch turns off. During overcurrent conditions that lower the output voltage, the error amplifier drives the COMP pin high, causing the switch to turn off.

Choosing SMD packages for the components used in the circuit design is advantageous in terms of compactness.

Circuit Diagram

All electronic components used in the project are:

• TPS54331 Buck Converter IC, SOIC-8

• Schottky Diode B340A, SMA

• Inductor 10uH, SMD 10×10

• LED Blue & Green, 1206

• Terminal Block 2x1, 5 mm

• Male Header 2x1, 2.54 mm

• Capacitors (ceramic, all values)

• Resistors (all values)