Synchronous buck controller ideal for stepping down high-voltage battery supply

STMicroelectronics

The STMicroelectronics L3751, which operates from a very wide input-voltage range of 6 V to 75 V, can step the input from a power distribution bus down to a power rail at 12 V or 5 V.

The L3751 from STMicroelectronics is a synchronous dc-dc step-down power controller which can support extreme voltage-conversion ratios with good power efficiency.

 

Operating from an input-voltage range of 6 V to 75 V, the L3751 provides an adjustable output of between 0.8 V and 60 V while switching at frequencies ranging from 100 kHz to 1 MHz. The controller is ideal for circuits that convert the output from a high-voltage battery or unregulated 24 V and 48 V bus to an application’s 12 V or 5 V power rail.

 

In diode emulation mode, the L3751 implements a pulse-skipping function which maximizes efficiency at light loads, and limits output-voltage ripple. Forced PWM operation over the entire load range holds the switching frequency constant, and also minimizes output-voltage ripple.

 

The controller features a Power Good output which validates the regulated output voltage: this is useful for implementing power sequencing during a digital IC power-up phase.

 

The L3751 includes 7.5 V gate drivers compatible with standard MOSFETs, eliminating the need for external gate drivers in a converter circuit. Embedded protection functions include output over-current, under-voltage lockout, internal voltage monitoring, and thermal shutdown. 

 

Developers can use the ST eDesignSuite software tool to configure the L3751 buck converter for the application. The tool is available at www.st.com/content/st_com/en/campaigns/edesignsuite-edsim-simulation-tool-for-smps-and-analog-ics.html

Features

  • 40 ns minimum on-time
  • Internal voltage monitoring
  • Low drop-out operation during line transients
  • Adjustable soft-start or input-voltage tracking
  • Operating-temperature range: -40°C to 150°C

Applications

  • Telecoms and networking equipment
  • Fail-safe systems
  • Industrial equipment
STMicroelectronics — L3751 Buck Controller

Evaluation Board

Part Number: STEVAL-L3751V12

The STEVAL-L3751V12 demonstration board provides a regulated 5 V output at a switching frequency of 230 kHz. The output voltage can also be set to 12 V using a jumper connector, or to a different voltage by changing a resistor.

 

The STEVAL-L3751V12 board is rated for use with loads up to 100 W. The default maximum current is set to 15 A. It can be easily selected by changing a resistor.

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