Diodes AH285 User Manual
Ah285, Hall-effect smart fan motor controller, Description
AH285
HALL-EFFECT SMART FAN MOTOR CONTROLLER
AH285
Document number: DS31029 Rev. 8 - 2
1 of 9
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
R
pu
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.