STMicroelectronics L6911E

Overview

L6911E from STMicroelectronics is a 5-bit programmable synchronous step-down DC/DC controller for microprocessor core power supplies, featuring voltage-mode PWM control, ±1% output accuracy over line and temperature, 200 kHz internal oscillator (adjustable 50 kHz–1 MHz), and integrated overvoltage/overcurrent protection with HICCUP mode recovery. It drives external N-channel MOSFETs in buck topology with 1.050 V to 1.825 V output range in 25 mV binary steps.

For engineers reviewing the L6911E datasheet, L6911E pinout, L6911E application, or L6911E equivalent, key selection considerations include VID-programmable VRM 8.5 compliance, R_DS(ON)-based current sensing, adaptive dead-time gate drivers (1.3 A high-side source), OVP-triggered SCR crowbar support, and soft-start/inhibit control via external capacitor and logic-level input.

Technical Context

The L6911E implements voltage-mode PWM control using an internal 15 MHz GBW error amplifier with 10 V/µs slew rate, enabling fast transient response across 0–100% load steps. Its 5-bit DAC sets both output voltage and associated PGOOD/OVP thresholds via TTL-compatible VID pins, eliminating external resistive dividers.

Oscillator frequency is set by an external resistor on the RT pin - sinking current from RT to GND increases frequency (up to 1 MHz), while sourcing into RT from V_CC reduces it (down to 50 kHz); open-circuit yields 200 kHz. Protection logic uses VSEN monitoring, OCSET current-source-based upper-FET R_DS(ON) sensing, and dual OVP action: internal low-side turn-on plus external SCR drive via OVP pin.

Key Specifications

Pinout & Package

The L6911E is housed in a SO-20 (Small Outline, 20-pin) package with standard 0.65 mm pitch and exposed thermal pad - optimized for thermal dissipation in high-current DC/DC applications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ISL6522CRZ and TPS51100PWR, the L6911E offers broader frequency adjustability (50–1000 kHz), VRM 8.5–compliant 5-bit VID, and unique OVP-driven SCR crowbar support - making it optimal for legacy server/desktop VRMs requiring field-serviceable overvoltage safety.

Availability

L6911E is available at Aetrix Electronics and suitable for desktop motherboard power delivery, server VRM modules, embedded microprocessor supplies, and industrial FPGA core regulation requiring stable component supply across extended lifecycle programs.

Supply support for L6911E 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 computing markets.

The L6911E belongs to ST's VRM-compliant DC/DC controller product line, engineered specifically for high-efficiency, high-accuracy core voltage regulation in x86 microprocessor systems prior to VRM 10.x adoption.

FAQ

What is the minimum recommended external soft-start capacitor value for L6911E?

The L6911E charges the soft-start capacitor with a precise 10 µA current. To achieve a typical 10 ms ramp to full output, a 100 nF capacitor yields ~1 V at t = (1 V × 100 nF) / 10 µA = 10 ms. ST recommends 47–220 nF ceramic capacitors; values below 22 nF may cause instability, while >470 nF extends startup unnecessarily.

Can L6911E operate with a 5 V VCC supply while driving 12 V gate signals?

Yes - the L6911E supports VCC from 4.5 V to 12 V. When VCC = 5 V, the low-side driver operates directly from VCC, while the high-side driver uses the BOOT capacitor charged from PHASE and VCC via a diode. The datasheet confirms 600 mA high-side source current at V_BOOT–V_PHASE = 5 V, sufficient for most 5 V logic-level MOSFETs.

How does the L6911E implement overcurrent protection without a sense resistor?

It measures voltage drop across the upper MOSFET's R_DS(ON) using the OCSET pin. An internal 200 µA current source flows through an external resistor (R_OCSET) tied between OCSET and the MOSFET drain. When V_DS exceeds (200 µA × R_OCSET), overcurrent is triggered - eliminating the need for a separate sense resistor and associated power loss.

Is the L6911E pin-compatible with newer VRM controllers like the ISL6522?

No - the L6911E uses a 20-pin SO package with unique pin assignments (e.g., VSEN, OCSET, RT, OVP), while ISL6522 uses a 28-pin QFN with different signal mapping and integrated bootstrap diode. Direct replacement requires PCB redesign; functional equivalence exists only at the system level with careful attention to VID encoding, protection thresholds, and frequency configuration.