STMicroelectronics L6728ATR

Overview

L6728ATR from STMicroelectronics is a high-frequency single-phase synchronous buck PWM controller with integrated high-current gate drivers, 0.8 V internal reference, ±0.8 % output voltage accuracy, fixed 600 kHz switching frequency, and sensorless over-current protection via low-side R_DS(on) sensing - designed for CPU/DSP and subsystem power supplies requiring fast transient response and pre-bias start-up capability.

For engineers reviewing the L6728ATR datasheet, L6728ATR pinout, L6728ATR application, or L6728ATR equivalent, key selection considerations include its VFDFPN10 package footprint, LS-LESS pre-bias startup behavior, dual-level OCP programmability via ROCSET, and VSEN-based OVP/UVP/PGOOD monitoring independent of FB divider.

Technical Context

L6728ATR implements voltage-mode control with a 15 MHz GBWP error amplifier and 8 V/μs slew rate to support high-bandwidth regulation. Its adaptive anti-cross-conduction logic uses PHASE and LGATE pin sensing to dynamically adjust dead time, minimizing body-diode conduction without external Schottky diodes.

The controller supports input conversion down to 1.5 V while operating from a 5–12 V VCC supply. It enables sensorless current sensing by comparing PHASE node voltage during LS conduction against user-programmed (via ROCSET) and internally scaled (×1.5) OCP thresholds, eliminating sense resistors.

Key Specifications

Pinout & Package

Supplied in VFDFPN10 (3 × 3 mm, 0.5 mm pitch) with exposed thermal pad - optimized for high-power density DC-DC converters requiring efficient heat dissipation in space-constrained applications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ISL6269CRZ-T and TPS54620RGYR, L6728ATR uniquely combines sensorless OCP, LS-LESS startup, and VSEN-decoupled protections in a 10-pin VFDFPN - offering superior flexibility for high-reliability, high-density POL designs where discrete MOSFET optimization and robust sequencing are critical.

Availability

L6728ATR is available at Aetrix Electronics and suitable for CPU and DSP power supply, memory termination, subsystem power (MCH/IOCH), and distributed POL applications requiring stable component supply, long-lifecycle support, and consistent parametric performance across production batches.

Supply support for L6728ATR 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

L6728ATR belongs to ST's high-frequency PWM controller product line, engineered specifically for high-efficiency, space-constrained synchronous buck converters in computing and communications infrastructure where precision regulation and robust fault handling are mandatory.

FAQ

What is the purpose of the VSEN pin, and how does it differ from the FB pin?

VSEN is a dedicated output voltage monitor pin used exclusively for over-voltage, under-voltage, and PGOOD protection functions. Unlike FB - which feeds the error amplifier for regulation - VSEN operates independently, allowing accurate protection even if the FB resistor divider fails or disconnects. It must be connected directly to the output or to the same node as the FB divider's top resistor to ensure coordinated regulation and protection thresholds.

How does LS-LESS startup prevent negative voltage spikes during pre-biased output conditions?

During LS-LESS startup, the low-side MOSFET remains disabled until the high-side MOSFET begins switching. This prevents reverse current flow through the inductor when the output is already charged above the target voltage. If the output remains pre-biased after soft-start completes, the LS MOSFET is then enabled to discharge the output safely to the regulated level - avoiding dangerous undershoot and load damage.

Can the L6728ATR operate with an input voltage below 5 V, and what are the limitations?

Yes - the power conversion input can be as low as 1.5 V, but the VCC supply must remain within 5–12 V. The controller itself is powered from VCC, not VIN. Therefore, a separate 5–12 V bias supply (e.g., auxiliary rail or LDO) is mandatory. The 1.5 V minimum applies only to the switched input (VIN), enabling use in intermediate bus architectures such as 3.3 V or 5 V input-to-core-voltage conversion.

What happens when over-current protection is triggered, and how is recovery performed?

Upon detection of a second-level OCP event (exceeding 1.5× programmed threshold), or four consecutive first-level OCP events, the controller latches both UGATE and LGATE low and halts switching. Recovery requires cycling the VCC supply - i.e., removing and reapplying the 5–12 V bias voltage - to reset internal protection latches and restart soft-start. No automatic retry or hiccup mode is implemented.