DC to DC Buck Converter Based on L3751 Controller-Perceptive Electronic Components

DC to DC Buck Converter Based on L3751 Controller

Published Time: 2023-03-14 14:57:38

DC Input 6 V to 75 V Wide Voltage Range STEVAL-L3751V12 Synchronous Buck Evaluation Board has extreme voltage conversion ratio at switching frequency.

Introduce

DC Input 6 V to 75 V Wide Voltage Range STEVAL-L3751V12 Synchronous Buck Evaluation Board has extreme voltage conversion ratio at switching frequency. The board provides a regulated 5 V output at a switching frequency of 230 kHz. The output voltage can easily be set to 12 V using jumper connectors.

A different voltage output can be selected by changing the resistor to a lower VIN range.

The STEVAL-L3751V12 is a 100 W demonstration board. The default maximum current setting is 15 A. You can easily choose to change a resistor in the following ways. The evaluation board is based on the L3751 synchronous buck controller implementing a voltage-mode wrapper in a VQFN. Diode emulation (DEM) implements pulse-skipping mode to maximize efficiency at light loads with controlled output voltage ripple.

Forced PWM (FPWM) overload range keeps switching frequency constant and minimizes output voltage ripple. A power-good open-collector output verifies the regulated output voltage for monitoring. It enables output voltage sequencing of digital ICs during power-up phase. Embedded gate drivers are designed for standard Vth MOSFETs, minimizing external component count. Embedded protections such as output overcurrent, input voltage UVLO, internal voltage monitoring, and 150°C thermal shutdown in telecom, networking, and industrial applications.

You can use the eDesignSuite software tool to configure the L3751 buck converter and meet your application requirements.

How to use the board

STEVAL-L3751V12 is configured through L3751 with adjustable VOUT. The board is set up to provide 5 V or 12 V output voltage (see Section 3.4 Signal Manager - J5), FSW = 230 kHz.

To use this board, follow the steps below.

Step 1. Connect the supply voltage between the VIN and GND connectors.

Step 2. Connect a load (power resistor or active load) between the VOUT and GND connectors.

NOTE: We recommend using a short wire to connect steps 1 and 2.

Step 3. Set the supply voltage VIN from 6 to 75 V, VOUT = 5 V, or set VIN from 13 to 75 V, VOUT = 12 V.

Step 4. To reach IoutMax, increase active load or decrease power resistor.

External airflow is recommended to reduce heating of the board.

Board Setting Capability

The STEVAL-L3751V12 overcurrent limit is set to 18 A (average) through R5. By increasing or decreasing this resistor, the current limit can be increased or decreased (check the datasheet or eDesignSuite further for details). The switching frequency is set by R10. It can be changed from 100 KHz to 1 MHz. Consider that increasing Fsw will generate a lot of self-heating (see datasheet or eDesignSuite for further details).

The STEVAL-L3751V12 is a 100 W power evaluation board. Therefore, when VOUT = 5 V, IoutMax = 15 A, IoutMax = 10 A for VOUT = 12 V. For high output power, we recommend 200 LMF airflow to reduce self-heating and avoid OTP. High input current increases EMI inductor temperature. In this case, it can be achieved by using R18 = 0 Ω or choosing an inductor with a higher Irms.

VIN UVLO is set to 14.5V. However, the VIN UVLO partition can be changed by changing R9 and R19 (see datasheet or eDesignSuite for more details). VOUT can be selected from a range of 5.07 V to 12.18 V using J1. VOUT1 and VOUT2 can be varied by choosing different values for R12, R13 and R21.

• VOUT1→Pin 6 to GND→VOUT = (1+(R12+R11)/(R13//R21)) x VFB, where VFB is fixed at 0.8 V.

• VOUT2 → pin 6 floating → VOUT = (R11+R12+R13)/R13 x VFB where VFB is fixed at 0.8 V (see L3751 datasheet for more details).

►Scene Application Diagram