US890 / US891
Two-Coil Fan Driver – High Output Current
Features and Benefits
Peak output current up to 1200mA
Low start-up voltage
Low output resistance
High sensitivity integrated Hall Sensor
Power-efficient CMOS and power MOSFETs
Built-in output protection clamping diode
Locked rotor protection and auto-restart
Integrated tachometer (US890) or alarm (US891)
signal protected output
Low cost
2-coil fan driver with FG/RD output in
RoHS Compliant 4-pin VK package
Application Examples
5V/12V DC brushless motor/fan
PC, server, laptop cooling fan
Power supply cooling fan
Large and small fan size
Ordering Information
Part No.
US890
US891
Temperature Code
E (-40° to 85°
C
C)
E (-40° to 85°
C
C)
Package Code
VK (4-pin TO-92)
VK (4-pin TO-92)
1 Functional Diagram
2 General Description
The US890/891 is a one-chip solution for driving
two-coil brushless DC motors and fans.
Based on the advanced Melexis CMOS process,
the IC contains a Hall-effect sensor, dynamic
offset correction and powerful output drivers with
1200mA peak output current capability.
Specially designed for driving large fans, the
device is optimized for low start-up voltage.
Frequency Generator or Rotation Detection is
available. The open-drain output makes easier the
connectivity with any external interface such as
hardware monitoring or Super I/O IC.
These features are combined with the Melexis
patented no-V
DD
design to fit the IC in a small 4-
pin VK package.
3901000890
Rev 002
Page 1 of 12
Data Sheet
Sep/07
US890 / US891
Two-Coil Fan Driver – High Output Current
Table of Contents
1 Functional Diagram ........................................................................................................ 1
2 General Description........................................................................................................ 1
3 Glossary of Terms .......................................................................................................... 3
4 Absolute Maximum Ratings ........................................................................................... 3
5 Pin Definitions and Descriptions................................................................................... 3
6 General Electrical Specifications .................................................................................. 4
7 Magnetic Specifications ................................................................................................. 4
8 Driver Output vs Magnetic Pole..................................................................................... 4
9 Detailed General Description ......................................................................................... 5
10 Unique Features............................................................................................................ 5
11 Performance Graphs .................................................................................................... 7
11.1 R
DSON
vs T
A
............................................................................................................... 7
11.2 R
DSON
vs V
DD
............................................................................................................. 7
11.3 Magnetic parameters vs T
A
....................................................................................... 7
11.4 Magnetic parameters vs V
DD
..................................................................................... 7
11.5 I
DD
vs T
A
.................................................................................................................... 7
11.6 I
DD
vs V
DD
.................................................................................................................. 7
12 Test conditions ............................................................................................................. 8
12.1 V
DD
– operating ......................................................................................................... 8
12.2 R
DSON
........................................................................................................................ 8
12.3 I
DD
............................................................................................................................. 8
12.4 FG/RD Output Low Voltage ...................................................................................... 8
13 Application Information................................................................................................ 9
13.1 Typical application circuit .......................................................................................... 9
13.2 Recommended circuit for ground disconnection protection....................................... 9
14 Application Comments ................................................................................................. 9
15 Standard information regarding manufacturability of Melexis products with
different soldering processes......................................................................................... 10
16 ESD Precautions ......................................................................................................... 10
17 VK Package Information (4-pin TO-92)...................................................................... 11
18 Disclaimer.................................................................................................................... 12
3901000890
Rev 002
Page 2 of 12
Data Sheet
Sep/07
US890 / US891
Two-Coil Fan Driver – High Output Current
3 Glossary of Terms
Two-coil fan
MilliTesla (mT), Gauss
V
DD
I
DD
Peak output current
Continuous output current
Locked rotor
FG
RD
A fan with two-coil windings where current alternates from 1 coil to the other
depending on the direction of the magnetic field.
Units of magnetic flux density :
1mT = 10 Gauss
Voltage on the common point of the fan coils.
Current supplying the chip which flows through the coil connected to the
switched off output driver.
The current flowing in the coil at start-up, only limited by the coil resistance
R
COIL
and the output driver resistance R
DSON.
The average current flowing in the coil when the fan is spinning normally.
The state when the fan stopped spinning due to mechanical blockage.
Frequency generator or tachometer output
Rotation detection or alarm output
4 Absolute Maximum Ratings
Parameter
Symbol
Fan Supply Voltage
V
DD
Peak Output Current
I
OUTp
Continuous Output Current
I
OUTc
FG/RD Pull-Up Voltage
V
FG, RD
FG/RD Reverse Current
I
FG_REV, RD_REV
Operating Temperature Range
T
A
Junction Temperature
T
J
Storage Temperature Range
T
S
Magnetic Flux Density
B
ESD Sensitivity (AEC Q100 002)
-
Table 1: Absolute maximum ratings
Value
18
1200
600
18
60
-40 to 85
125
-55 to 150
Unlimited
4
Units
V
mA
mA
V
mA
°C
°C
°C
mT
kV
Exceeding the absolute maximum ratings may cause permanent damage. Exposure to absolute-maximum-
rated conditions for extended periods may affect device reliability.
5 Pin Definitions and Descriptions
Pin Name
Pin number
Function
FG (RD)
1
Frequency Generator (Rotation Detection) Open Drain Output
OUT1
2
Open Drain Coil Driver 1
OUT2
3
Open Drain Coil Driver 2
GND
4
Ground pin
Table 2: Pin definitions and descriptions
3901000890
Rev 002
Page 3 of 12
Data Sheet
Sep/07
US890 / US891
Two-Coil Fan Driver – High Output Current
6 General Electrical Specifications
DC Operating Parameters T
A
= 25 C, V
DD
= 12V (unless otherwise specified)
Parameter
Fan Supply Voltage
Supply Current
OUT1, OUT2 ON Resistance
OUT1, OUT2 ON Resistance
OUT1, OUT2 Output Clamp Voltage
FG / RD Output Low Voltage
FG / RD Output Clamp Voltage
FG / RD Output Leakage Current
FG / RD Output Current Limit
Package Thermal Resistance
Locked Rotor Period
Locked Rotor Period
Locked Rotor Period
Locked Rotor Period
Output Switching Delay
Table 3: Electrical specifications
Symbol
V
DD
I
DD
R
DSON 1,2
R
DSON 1,2
V
OUT1,2
V
OL
V
CLMP
I
LEAK
I
FGLIM
R
TH
T
ON
T
OFF
T
ON
T
OFF
T
DELAY
Test Conditions
Operating – R
COIL
= 100Ω
V
DD
= 5V, T
A
= 25°C, I
OUT
= 300mA
V
DD
= 5V, T
J
= 125°C, I
OUT
= 300mA
36
I
OL
= 4mA
18
V
FG
(V
RD
) = 5V
V
FG
(V
RD
) = 12V
One-sided PCB, zero LFPM
V
DD
> 7V
V
DD
> 7V
V
DD
< 5.5V
V
DD
< 5.5V
“Dead time” when both drivers are off
0.33
25
0.15
23
200
0.25
1.5
0.53
(2)
3.2
(2)
50
0.5
10
Min
2.6
(1)
Typ
12
2.5
1
1.8
Max
18
4
1.4
2.5
Units
V
mA
Ω
Ω
V
V
V
A
mA
°C/Watt
s
s
s
s
µs
o
0.37
2.25
0.75
4.51
Note 1: The minimal value of V
DD
should be determined using the following equation:
V
DD
=2.5V + R
COIL
* I
DD
Note 2: Typical values valid at 5.5V. The values increase at lower voltage to improve fan start-up reliability.
7 Magnetic Specifications
DC Operating Parameters T
A
= 25 C, V
DD
= 12V (unless otherwise specified)
Parameter
Symbol
Test Conditions
Operate point
B
OP
Release point
B
RP
Hysteresis
B
HYST
Table 4: Magnetic specifications
Min
0
-6
2
Typ
Max
6
0
10
Units
mT
mT
mT
o
4.5
8 Driver Output vs Magnetic Pole
Parameter
North pole
South pole
Test Conditions
B < Brp
B > Bop
OUT1
High
Low
OUT2
Low
High
FG
High
Low
Table 5: Driver output vs magnetic pole
Note 1: The magnetic pole is applied facing the branded side of the package
3901000890
Rev 002
Page 4 of 12
Data Sheet
Sep/07
US890 / US891
Two-Coil Fan Driver – High Output Current
9 Detailed General Description
The US890/891 is a one-chip solution for driving two-coil brushless DC motors and fans. Based on advanced
Melexis CMOS process, the chip contains a Hall-effect sensor, dynamic offset correction and powerful output
drivers with 1200mA peak output current capability.
The low side output coil drivers are fully protected against switching transients. So an external zener diode is
not needed to cut the high voltage spikes induced by the motor coils.
The US890 has an open-drain integrated tachometer FG output that follows the Hall signal.
In the US891, the open-drain rotation detection output RD is active low during normal spinning of the motor. It
goes high when the flux switching frequency becomes too low, which means the motor is blocked.
10 Unique Features
Specially designed for driving large fans, both ICs have LRP characteristics optimised for low start-up
voltage. At low V
DD
, fans typically take longer to start up than at higher V
DD
.
The motor start-up phase (from zero to maximum rotation speed) is illustrated below. Big fans with large
inertia may have slow start-up causing a longer first output pulse after power-on. If this pulse duration is
longer than the LRP T
ON
period, the fan may falsely enter locked rotor condition.
The US890/891 provides an adequate and simple solution to prevent this by automatically adjusting the LRP
period at low voltage. It directly improves the motor start-up reliability.
3901000890
Rev 002
Page 5 of 12
Data Sheet
Sep/07
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