Diodes Incorporated AH291-PG-B

Overview

AH291-PG-B from Diodes Incorporated is a monolithic Hall-effect smart fan motor controller for two-coil BLDC cooling fans, integrating an on-chip Hall sensor, complementary open-collector drivers (DO/DOB), rotor-lock detection, automatic restart, and built-in Zener protection. It operates from 1.8V to 5.75V, delivers 400mA average output current, and supports SIP-4L and SOT89-5L packages for compact thermal management in low-voltage cooling systems.

For engineers reviewing the AH291-PG-B datasheet, AH291-PG-B pinout, AH291-PG-B application, or AH291-PG-B equivalent, key selection criteria include rotor-lock protection timing (TRLP-ON = 0.4s, TRLP-OFF = 2.4–3.6s), output saturation voltage (≤600mV at 350mA), magnetic sensitivity (Bop = 30–60 Gauss), and dual-package availability for board-space-constrained thermal designs.

Technical Context

The AH291 implements a Hall-plate-based commutation control loop with integrated lock-detection logic that monitors back-EMF absence and triggers periodic shutdown/restart cycles during rotor stall. Its regulator supplies internal circuitry while maintaining operation down to 1.8V, though magnetic performance stabilizes only above 2.0V.

Complementary DO and DOB outputs drive external fan coils in push-pull configuration; each features 1.75Ω R_DS(ON), 15V Zener clamping, and 700mA peak current capability. The truth table defines rotating mode (H/L or L/H inputs) versus lockup mode (both inputs high), enabling deterministic state transitions without external microcontroller intervention.

Key Specifications

Pinout & Package

Available in SIP-4L (4-pin single-inline package) and SOT89-5L (5-pin surface-mount package). SIP-4L provides minimal footprint for axial fan PCBs; SOT89-5L offers higher power dissipation and NC pin for grounding or decoupling options.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Hall-effect BLDC fan controller applications.

Compared with A3921KLPTR-T and NCP170B, AH291-PG-B uniquely integrates Hall sensing, dual-driver outputs, and autonomous lock-recovery in a single 1.8–5.75V package-making it the only drop-in solution for space-constrained, low-voltage BLDC fan modules requiring zero external active components.

Availability

AH291-PG-B is available at Aetrix Electronics and suitable for server CPU cooling fans, network switch heat-sink fans, and industrial PLC enclosure fans requiring stable component supply across extended production lifecycles.

Supply support for AH291-PG-B 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, specializing in high-reliability power management, signal integrity, and motion control solutions for industrial, computing, and communications markets.

AH291-PG-B belongs to Diodes' Smart Motor Control product line, engineered specifically for cost-sensitive, low-voltage BLDC fan applications where integration, thermal resilience, and autonomous fault recovery are critical design requirements.

FAQ

What is the minimum supply voltage required for reliable Hall sensor operation?

The AH291-PG-B begins switching outputs at 1.8V, but its Hall sensor achieves stable magnetic response only above 2.0V. Below this threshold, Bop and Brp values shift unpredictably, risking missed commutation or false lock detection. Designers must ensure Vdd remains ≥2.0V during startup and transient conditions.

Can AH291-PG-B drive a three-phase BLDC fan?

No. AH291-PG-B is strictly a two-phase (bipolar) controller with complementary DO/DOB outputs. It lacks third-phase drive capability, Hall input decoding for six-step commutation, or timing logic for trapezoidal waveform synthesis. It is designed exclusively for two-coil axial fans with internal permanent magnet rotors.

How does the rotor-lock protection behave under continuous obstruction?

When rotor lock is detected, AH291-PG-B disables both outputs for 0.4 seconds (TRLP-ON), then re-enables them for 2.4–3.6 seconds (TRLP-OFF). This cycle repeats indefinitely until rotation resumes. No external watchdog or reset is needed-the IC manages timing autonomously using internal RC oscillators.

Is the NC pin on the SOT89-5L package electrically isolated?

Yes. The NC pin in the SOT89-5L package is not bonded to any internal die structure and has no electrical connection. It may be used as a mechanical anchor, grounded for EMI reduction, or left unconnected-none of these choices affect device functionality or specifications.