Diodes Incorporated AH285-PL-B

Overview

AH285 from Diodes Incorporated is a Hall-effect smart fan motor controller IC for two-coil brushless DC (BLDC) cooling fans, integrating a Hall sensor, dynamic offset correction, dual complementary open-drain drivers (500mA avg), Rotor Lock Protection with auto-restart, and tachometer (FG) output. It operates from 3.8V to 20V and is packaged in SOT89-5.

For engineers reviewing the AH285 datasheet, AH285 pinout, AH285 application, or AH285 equivalent, key selection considerations include its integrated Hall sensing, FG frequency generation tied to magnetic change rate, Rotor Lock Protection timing (0.4–0.6s on, 2.4–3.6s off), Zener-protected outputs, and SOT89-5 thermal performance (θJA = 156°C/W).

Technical Context

The AH285 implements a closed-loop commutation control architecture using an on-chip Hall plate and amplifier to detect rotor position, feeding logic that drives complementary DO/DOB outputs with built-in Zener clamping (35–60V breakdown). Its lock detection circuit monitors back-EMF absence and initiates shutdown after 0.5s typical, then re-enables drive after 3s typical once rotation resumes.

The FG output delivers an open-drain square wave whose frequency equals the magnetic pole transition rate - directly proportional to motor RPM - while VDD regulation and thermal foldback (PD derating from 800mW at 25°C to 0mW at 150°C) ensure stable operation across -40°C to +100°C ambient.

Key Specifications

Pinout & Package

SOT89-5 package with exposed thermal pad (pin 3 = GND), 1.5mm pitch, 4.5mm × 2.5mm footprint, and 1.5mm height - optimized for surface-mount fan PCBs with minimal board area and direct thermal conduction to copper pour.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AH2985, the AH285 offers proven field reliability but wider magnetic hysteresis and higher IDD; versus A3977, it delivers full integration (sensor + logic + drivers + FG) at the cost of stepper flexibility - making AH285 optimal for cost-sensitive, volume BLDC fan applications where simplicity and BOM reduction are primary goals.

Availability

AH285 is available at Aetrix Electronics and suitable for server rack cooling fans, industrial enclosure ventilation fans, medical diagnostic equipment fans, and telecom base station heat sink fans requiring stable component supply despite its NRND status.

Supply support for AH285 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 power management, signal integrity, and protection solutions for industrial, computing, and consumer markets.

The AH285 belongs to Diodes' Hall-effect motor controller product line, designed specifically to replace multi-component fan drive solutions with single-chip integration for cost-sensitive, high-volume BLDC cooling applications.

FAQ

What is the function of the FG pin on the AH285?

The FG (Frequency Generator) pin is an open-drain output that produces a square wave whose frequency equals the rate of magnetic pole transitions sensed by the internal Hall element - directly proportional to motor RPM. It requires an external pull-up resistor and interfaces directly with microcontroller input capture or counter peripherals for speed monitoring without additional signal conditioning.

How does Rotor Lock Protection work and what are its timing parameters?

Rotor Lock Protection detects absence of magnetic transitions for ≥0.4s (min), triggering immediate shutdown of both DO and DOB outputs. After lock removal, the device remains disabled for 2.4–3.6s (typical 3s) before automatically re-enabling drive - preventing repeated lock attempts and allowing mechanical reset. This behavior is fully internal and requires no external components.

Can the AH285 drive three-phase BLDC fans?

No. The AH285 is designed exclusively for two-coil (single-phase commutated) brushless DC fans and motors. Its dual complementary outputs (DO/DOB) and Hall sensing architecture support only 180° conduction with two windings. Three-phase BLDC operation requires six-step commutation and three half-bridge drivers - beyond the AH285's functional scope.

Is the AH285 RoHS-compliant and halogen-free?

Yes. The AH285 is fully RoHS-compliant (2011/65/EU), lead-free, and halogen- and antimony-free - classified as a "Green" device per Diodes Incorporated's definition: <900ppm bromine, <900ppm chlorine (<1500ppm total Br+Cl), and <1000ppm antimony compounds - verified per material declarations and test reports.