Diodes AH285 User Manual
AH285
HALL-EFFECT SMART FAN MOTOR CONTROLLER
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
(Top View)
Vdd
1
GND
2
3 7
285
FG
5
DOBDO
4
SOT89-5L
Applications
• Two-coil BLDC cooling fans
• Low to medium voltage, low power BLDC motors
(12V)
D2
R
D1
pu
C3
5 4
285
132
GND
R1
C1
Coil2
Coil1
R2
C2
Typical Application Circuit
Vdd
FG
D3
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 2.2μF E-Cap capacitor for C1, C2 and C3. These values
AH285
Document number: DS31029 Rev. 8 - 2
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.
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Pin Descriptions
Pin Name Description
FG Frequency Generation
Vdd Input Power
DO Output Pin
DOB Output Pin
GND Ground
Functional Block Diagram
Vdd
AH285
HALL-EFFECT SMART FAN MOTOR CONTROLLER
Lock detect,
shutdown and
automatic re-start
Regulator
Hall
Plate
Amp.
Control Logic
DO
DOB
GND
FG
AH285
Document number: DS31029 Rev. 8 - 2
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AH285
θJAθ
HALL-EFFECT SMART FAN MOTOR CONTROLLER
Absolute Maximum Ratings (T
Symbol Characteristics Rating Unit
Vdd Supply Voltage 24 V
IO Output Current
PD Power Dissipation 800 mW
TST Storage Temperature -55 ~ 150
TJ Maximum Junction Temperature 150
θ
Thermal Resistance Junction to Case (Note 2) 156
JA
= 25°C)
A
TJ
TA
JC
I
500 mA
O (AVE)
I
O (PEAK)
Tc
700 mA
°C
°C
°C/W
Notes: 2. θJA should be confirmed with heat sink thermal resistance. If there is no heat sink contact, θJA will almost be the same as θJC..
Recommended Operating Conditions
Symbol Characteristic Conditions Min Max Unit
Vdd Supply Voltage Operating 3.8 20 V
TA Operating Ambient Temperature Operating -40 100
°C
AH285
Document number: DS31029 Rev. 8 - 2
3 of 9
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June 2010
© Diodes Incorporated
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