STMicroelectronics L6728

Overview

L6728 from STMicroelectronics is a single-phase synchronous buck PWM controller with integrated high-current gate drivers, 0.8 V internal reference, ±0.8 % output voltage accuracy, fixed 300 kHz switching frequency, and sensorless overcurrent protection via low-side R_DS(on) sensing - used in CPU/DSP and memory power supplies requiring precise regulation down to 0.8 V.

For engineers reviewing the L6728 datasheet, L6728 pinout, L6728 application, or L6728 equivalent, key selection considerations include its DFN10 package footprint, programmable dual-level OCP using LGATE/OC pin, PGOOD output with 0.89 V nominal threshold, and LS-less pre-bias startup capability for safe operation on already-biased rails.

Technical Context

L6728 implements voltage-mode control with a 15 MHz gain-bandwidth error amplifier and 8 V/μs slew rate, enabling fast transient response in DC-DC converters. Its adaptive dead-time logic monitors PHASE and LGATE to prevent shoot-through while minimizing body-diode conduction without external Schottky diodes.

The controller supports input conversion as low as 1.5 V while operating from a separate 5–12 V VCC supply. It features internal soft-start (4.5 ms), disable function via COMP/DIS pin (<0.75 V), and VSEN-based OVP/UVP with latched thresholds at 1.000 V and 0.600 V respectively.

Key Specifications

Pinout & Package

Supplied in a compact 3×3 mm DFN10 package with exposed thermal pad for enhanced power dissipation (R_th(JC) = 5 °C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck controller applications.

Compared with ISL6263CRZ and TPS54620RGYR, L6728 uniquely combines sensorless R_DS(on) OCP, VSEN-based protections, and LS-less startup in a DFN10 package - making it optimal for space-constrained, high-reliability CPU/memory rails where pre-bias safety and fault coverage are critical.

Availability

L6728 is available at Aetrix Electronics and suitable for CPU core power supply, memory termination supply, and subsystem power (MCH/IOCH) requiring stable component supply despite its obsolete status per STMicroelectronics documentation.

Supply support for L6728 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

L6728 belongs to ST's high-performance power controller product line, designed specifically for efficient, compact, and robust point-of-load regulation in computing and communications infrastructure.

FAQ

What is the purpose of the LGATE/OC pin on L6728?

The LGATE/OC pin serves dual functions: it outputs the low-side MOSFET gate drive signal and sources a precise 10 μA current during startup to program the first-level overcurrent threshold via an external ROCSET resistor. This enables sensorless current limiting without adding a sense resistor, directly leveraging the MOSFET's R_DS(on) for cost and space savings.

How does L6728 handle pre-biased output conditions during startup?

L6728 implements LS-less startup: during soft-start, the low-side driver remains disabled until the high-side begins switching. If the output is pre-biased above the target voltage, the high-side never turns on - so after 4.5 ms, the low-side is enabled to discharge the output to the regulated level. This prevents dangerous negative voltage spikes and ensures safe start-up on powered-backplane systems.

Can L6728 regulate output voltages higher than 0.8 V?

Yes - L6728 regulates higher outputs using a resistor divider from VOUT to FB and from FB to GND. With its 0.8 V internal reference, setting ROS = 100 kΩ and RFB = 10 kΩ yields a 8.8 V output. The FB pin draws only 100 nA bias current, minimizing divider error and enabling accurate scaling across wide output ranges.

What protection features does L6728 provide beyond overcurrent?

Beyond dual-level OCP, L6728 integrates overvoltage (OVP: 1.000 V), undervoltage (UVP: 0.600 V), and VSEN disconnection protection - all monitored independently on the VSEN pin. It also includes UVLO on VCC (4.1 V turn-on), PGOOD latching, and adaptive dead-time control to prevent shoot-through, delivering comprehensive fault coverage in a single IC.