STMicroelectronics L6731D

Overview

L6731D from STMicroelectronics is an adjustable step-down controller with synchronous rectification dedicated to DDR memory supply and termination rail applications. The controller drives external N-channel MOSFETs in a synchronous buck topology, supports an input voltage range from 1.8 V to 14 V, operates from a 4.5 V to 14 V supply, and regulates output voltage down to 0.6 V with high reference accuracy.

For engineers reviewing the L6731D datasheet, L6731D pinout, L6731D application, or L6731D equivalent, this controller is most relevant for DDR memory supply, DDR termination supply, low-voltage distributed DC/DC converters, high-current niPoL converters, compact DC/DC modules, and graphic-card power rails requiring source / sink capability, programmable MOSFET RDS(on) overcurrent sensing, selectable 250 kHz / 500 kHz operation, and HTSSOP16 exposed-pad assembly.

Technical Context

L6731D uses fixed-frequency voltage-mode PWM control and drives a high-side and low-side external MOSFET pair through HGATE and LGATE. The device supports 0% to 100% duty cycle and minimum on-time below 100 ns, allowing very low conversion ratios such as low-voltage DDR rails generated from higher intermediate buses.

For DDR applications, the DDR-IN pin selects internal or external reference operation and determines switching frequency. The internal divider and buffer generate VTTREF at one-half of DDR-IN, and the controller can regulate VTT and VTTREF within 1% of VDDQ. Protection functions include high-side peak current limit, low-side valley current limit, overvoltage protection, feedback disconnection detection, thermal shutdown, power-good monitoring, and hiccup behavior after overcurrent events outside soft-start.

Key Specifications

Pinout & Package

L6731D is supplied in an HTSSOP16 exposed-pad package with 0.65 mm lead pitch and compact 16-pin surface-mount construction. The exposed-pad TSSOP format helps route gate-drive, phase-node, feedback, DDR reference, and current-limit signals in a small synchronous buck layout while improving ground connection and thermal transfer from the controller package to the PCB.

Key Features

• Adjustable synchronous step-down controller dedicated to DDR memory supply and termination rails.
• 1.8 V to 14 V converter input range and 4.5 V to 14 V controller supply range.
• Output voltage adjustable down to 0.6 V with ±0.8% reference accuracy over line and temperature.
• VTT and VTTREF regulation within 1% of VDDQ for DDR memory requirements.
• Selectable 250 kHz / 500 kHz fixed-frequency voltage-mode control.
• High-current MOSFET drivers with predictive anti-cross-conduction control and source / sink capability.
• Programmable high-side and low-side RDS(on) overcurrent sensing without a dedicated current-sense resistor.
• Power-good output, soft-start / inhibit, overvoltage protection, hiccup-mode OCP, and thermal shutdown.

Applications

Equivalent & Alternatives

When evaluating L6731D equivalent devices, engineers should compare DDR reference behavior, input voltage range, output-voltage accuracy, switching frequency, high-side and low-side driver capability, RDS(on) current-limit method, source / sink operation, HTSSOP16 footprint, and production packaging format.

Compared with L6731DTR, L6731D keeps the same DDR memory supply controller function, pinout, HTSSOP16 package, MOSFET driver structure, and protection behavior. L6731D vs L6731DTR selection depends mainly on tube versus tape-and-reel packaging requirements rather than electrical redesign.

Quality

L6731D should be sourced as original STMicroelectronics components through traceable and controlled supply channels. Quality verification procedures may include HTSSOP16 exposed-pad package inspection, top-mark validation, tube label review, solderability testing, VCCDR regulator output verification, DDR-IN reference behavior checks, HGATE / LGATE driver function testing, PGOOD threshold verification, current-limit setting review, and incoming inspection according to DDR memory power-supply production requirements.

Availability

L6731D is available at Aetrix Electronics and suitable for DDR memory supplies, DDR termination rails, low-voltage distributed DC/DC modules, graphic-card power rails, and compact synchronous buck converter designs requiring stable component supply and repeatable production support.

Supply support may include scheduled delivery planning, volume procurement support, BOM continuity assistance, traceable sourcing management, and long-term availability support for OEM manufacturers, memory-module power designers, graphic-card hardware developers, industrial computing builders, and electronics production programs.

For production deployment, confirming the HTSSOP16 exposed-pad package, tube packaging format, DDR-IN reference mode, switching frequency setting, MOSFET driver requirements, current-limit design, thermal requirements, environmental specifications, and sourcing continuity helps reduce procurement risk and improve manufacturing stability.

Manufacturer

STMicroelectronics supplies power-management ICs, controllers, converters, RF devices, discrete semiconductors, sensors, and embedded semiconductor products for computing, industrial, automotive, communication, and consumer systems. L6731D belongs to ST's synchronous step-down controller portfolio for DDR memory and low-voltage point-of-load power conversion.

FAQ

What is L6731D used for?

L6731D is used to control synchronous buck converters for DDR memory supply, DDR termination supply, low-voltage distributed DC/DC rails, niPoL converters, compact DC/DC modules, and graphic-card power rails. It drives external N-channel MOSFETs and can source or sink current, which is important for DDR termination rail behavior.

How does L6731D support DDR memory power requirements?

L6731D includes a DDR-IN input, internal divider, and VTTREF buffer. It can regulate VTT and VTTREF within 1% of VDDQ, and it supports an external reference from 0 V to 2.5 V for DDRI and DDRII requirements. This allows the controller to handle both fixed low-voltage buck regulation and DDR tracking reference behavior.

What switching frequencies can L6731D use?

L6731D supports two fixed switching-frequency options: 250 kHz and 500 kHz. The selection is made through the voltage condition at DDR-IN. Engineers choose the frequency based on inductor size, switching loss, transient response, output ripple, MOSFET selection, and EMI behavior.

How does L6731D implement overcurrent protection?

L6731D senses current through the RDS(on) of the external MOSFETs rather than requiring a separate current-sense resistor. The OCH pin sets high-side peak current limit, while the OCL pin sets low-side valley current limit. This dual-threshold approach helps protect both on-time and off-time current conditions in high-current synchronous buck converters.

What should be considered in L6731D PCB layout?

L6731D layout should keep PGND close to the low-side MOSFET source, route PHASE carefully because it is both a switching node and current-limit sensing node, place the bootstrap capacitor close between BOOT and PHASE, bypass VCCDR with at least 1 µF ceramic capacitance, and keep FB / COMP compensation traces away from noisy gate-drive and switching-current paths.

What package is used by L6731D?

L6731D uses an HTSSOP16 exposed-pad package. The package supports compact synchronous buck controller placement and provides an exposed pad for improved grounding, thermal transfer, and mechanical stability compared with a standard non-exposed TSSOP package.

What is the difference between L6731D and L6731DTR?

L6731D and L6731DTR use the same controller architecture, package, pinout, and electrical function. The key difference is packaging logistics: L6731D is supplied in tube packaging, while L6731DTR is supplied in tape-and-reel packaging for automated production assembly.