MLX90285
24V Low Noise Two-Coil Fan Driver
7 Magnetic Specifications
DC Operating Parameters TJ = 25°C, VDD = 5 to 30V (unless otherwise specified)
Parameter
Operate point
Release point
Hysteresis
Symbol
BOP
Min
0.5
-6
Typ
3
Max
6
Units
mT
BRP
-3
6
-0.5
mT
BHYST
2
mT
Table 3: Magnetic specifications
8 Driver Output vs Magnetic Pole
Parameter
North pole
South pole
Test Conditions
B < Brp – all packages
OUT1
High
Low
OUT2
Low
FG (6)
High
Low
B > Bop - all packages
Table 4: Driver output vs. magnetic pole (7)
High
9 Detailed General Description
The MLX90285 is a one-chip solution for driving two-coil brushless DC cooling fans.
Based on mixed-signal CMOS design, the device includes Hall-effect sensor with offset cancellation scheme, voltage
regulator, digital logic and power output drivers in a single package.
The MLX90285-FG version has an open-drain tachometer FG output that follows the Hall signal. This signal is used by
hardware monitoring system to determine the rotation speed of the fan.
In the MLX90285-RD version, the open-drain alarm output RD is a safety signal which allows detecting if the fan rotates or
not. It is active low during normal spinning of the motor. It goes high when the magnetic flux switching frequency drops
below nearly 1.15Hz (35RPM for 2 pole-pair fan)
The built-in locked rotor protection automatically shuts off the coil current when the rotor is mechanically blocked for more
than 0.43 second. The fan tries to restart every 3 seconds until the rotor is released. This on/off cycling reduces the average
current by factor of about 7. This protection prevents the fan to be overheated or damaged.
The device is based on the Melexis patented “no-VDD” design which removes the need of separate supply voltage pin for
two-coil fan. During operation, the power outputs are always operating as complementary, meaning also that one power
output is kept inactive while the other is active. Melexis cleverly turned this fact into benefit as “No-VDD” devices such as
MLX90285 recover the power supply through the inactive power output pin. Therefore, a separate supply voltage pin is not
required anymore and the device including logical output FG/RD can fit into a small 4-pin through-hole package VK.
In the application, the “No-VDD” design inherently isolates the IC behind the fan coils. Without direct output to the external
environment, the device is best protected against ESD and over-voltage issue on the power supply voltage line.
6 FG state is only valid during normal operation. In locked rotor protection, FG signal is high
7 The magnetic pole is applied facing the branded side of the package
3901090285
Rev. 005
Page 5 of 14
DataSheet
Aug/14
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