AH285

HALL-EFFECT SMART FAN MOTOR CONTROLLER

AH285

Document number: DS31029 Rev. 8 - 2

1 of 9

www.diodes.com

June 2010

© Diodes Incorporated

Description

The AH285 is a single-chip solution for driving two-coil

brushless direct current (BLDC) fans and motors. The device

includes a Hall-effect sensor, dynamic offset correction and

two complementary open-drain output drivers with internal

Zener diode protection.

To help protect the motor coils, the AH285 provides Rotor

Lock Protection which shuts down output drives if rotor lock is

detected. The device automatically re-starts when the rotor

lock is removed.

A Tachometer output is provided by open-drain Frequency

Generator (FG) Pin which allows external interface to monitor

motor rotation or speed. The FG output is the magnetic

change frequency.

The AH285 is available in SOT89-5L package.

Features

•

Single-chip solution

•

Operating Voltage: 3.8V to 20V

•

Built-in Hall sensor and input amplifier

•

Tachometer (FG) output

•

Rotor Lock Protection (Lock detection, output shutdown

and automatic re-start)

•

Built-in Zener protection for output driver

•

Average output current up to 500mA

•

Packaged in SOT89-5L

•

Green Molding Compound

Pin Assignments

1

2

3

74

5

DOB

DO

GND

FG

Vdd

SOT89-5L

285

(Top View)

Applications

•

Two-coil BLDC cooling fans

•

Low to medium voltage, low power BLDC motors

Typical Application Circuit

285

1

3

2

Vdd (12V)

Coil2

Coil1

FG

D2

D1

C3

5

4

GND

D3

R1

C1

R2

C2

12V DC Brush-less Fan with FG output function

Notes:

1. Typically it is recommended to us a 56 Ohm resistor for R1 and R2 and a 2.2

μF E-Cap capacitor for C1, C2 and C3. These values

may need to be optimized depending on the coils used.

To help with IC protection it’s advised to add a Zener diode between Vdd and ground. The Zener diode should be chosen to help

prevent the supply voltage exceeding the maximum rating of the device.