US651 / US661
Two-Coil Low Noise Fan Driver
Features and Benefits
Soft Switching for low noise applications
Slope control setting by dedicated pin
One-chip solution
(Hall + Drivers)
Advanced Protection
(enhanced locked rotor,
reverse voltage, thermal, output clamping)
Application Examples
5V/12V DC brushless motors
Continuous output current up to 350mA
Low noise brushless cooling fans
PC, server, laptop cooling fan
Power supply cooling fan
Large and small fan size
Integrated tachometer (US651) or
alarm (US661) signal output
Ordering Information
Part No.
US651
US661
Temperature Code
E (-40° to 85°
C
C)
E (-40° to 85°
C
C)
Package Code
DC (8-pin narrow SOIC8)
DC (8-pin narrow SOIC8)
1 Functional Diagram
2 General Description
The US651/661 is a one-chip solution for driving
two-coil brushless DC fan and motors. It is
especially suitable for relatively high-current rated
operation as it can drive up to 350mA continuous
output current.
The use of Melexis Soft Switching concept lowers
the acoustic and electrical motor noise and
provides smoother operation. This efficient
solution is combined with an innovative slope
control design controllable via a dedicated pin.
The device includes reverse voltage protection,
locked rotor protection and thermal protection.
Therefore, the IC robustness perfectly suits for
consumer and automotive-on-board applications.
Tachometer (FG) or Alarm (RD) open-drain output
is available. It makes the connectivity with external
interface such as hardware monitoring or Super
I/O IC easier.
The device is delivered in RoHS compliant DC
package (SMD) for automatic soldering
390109020902
Rev 002
Page 1 of 12
Preliminary Datasheet
Mar/07
US651 / US661
Two-Coil Low Noise Fan Driver
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 Output Behaviour vs Magnetic Pole.............................................................................. 5
9 Detailed General Description ......................................................................................... 5
10 Unique Features............................................................................................................ 6
10.1 Soft Switching & Slope setting.................................................................................................................6
10.2 Enhanced Locked Rotor Protection.........................................................................................................7
11 Performance Graphs .................................................................................................... 7
11.1 R
DSON
vs T
J
...............................................................................................................................................7
11.2 R
DSON
vs V
DD
............................................................................................................................................7
11.3 I
DD
vs T
J
....................................................................................................................................................7
11.4 I
DD
vs V
DD
.................................................................................................................................................7
11.5 Internal Slope Duration vs V
DD
................................................................................................................8
11.6 Slope Duration vs V
DD
..............................................................................................................................8
11.7 V
OL
vs. T
J
.................................................................................................................................................8
11.8 I
LEAK
vs. T
J
................................................................................................................................................8
11.9 I
FGLIM
vs. V
DD
............................................................................................................................................8
11.10 P
Dmax
vs. T
A
............................................................................................................................................8
12 Application Information................................................................................................ 9
13 Application Comments ................................................................................................. 9
14 Standard information regarding manufacturability of Melexis products with
different soldering processes......................................................................................... 10
15 ESD Precautions ......................................................................................................... 10
16 DC Package Information (8-pin narrow SOIC) .......................................................... 11
17 Disclaimer.................................................................................................................... 12
390109020902
Rev 002
Page 2 of 12
Preliminary Datasheet
Mar/07
US651 / US661
Two-Coil Low Noise Fan Driver
3 Glossary of Terms
Two-coil fan
MilliTesla (mT), Gauss
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
The current flowing in the coil at start-up, only limited by the coil resistance
R
COIL
and the output driver resistance R
DSON.
Average absolute value of the output current when the fan is spinning.
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
Supply Voltage
V
DD
FG / RD voltage
V
FG
(V
RD
)
Voltage on pin SLOPE
V
SLOPE
Peak output current
I
OUTp
Continuous output current
I
OUTc
Operating Temperature Range
T
A
Junction temperature
T
J
Storage Temperature Range
T
S
Magnetic flux density
B
Table 1: Absolute maximum ratings
Value
-12 to 18
-7 to 18
-0.5 to 18
700
350
-40 to 85
125
-55 to 150
Unlimited
Units
V
V
V
mA
mA
°C
°C
°C
mT
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 Function
FG (RD)
Tachometer (Alarm) open-drain output
VDD
Power Supply pin
SLOPE
Slope Control pin
OUT1
Open Drain Coil Driver 1
GND
Ground pin
OUT2
Open Drain Coil Driver 2
NC
Not connected
NC
Not connected
Table 2: Pin definitions and descriptions
Pin number (DC)
1
2
3
4
5
6
7
8
390109020902
Rev 002
Page 3 of 12
Preliminary Datasheet
Mar/07
US651 / US661
Two-Coil Low Noise Fan Driver
6 General Electrical Specifications
DC Operating Parameters T
J
= 25 C, V
DD
= 12V (unless otherwise specified)
Parameter.
Supply Voltage
Supply Current
OUT1, OUT2 ON Resistance
OUT1, OUT2 Clamp Voltage
FG / RD Output Low Voltage
FG / RD Output Clamp Voltage
FG / RD Output Leakage Current
FG / RD Output Current Limit
Output Switching Slope Duration
(1)
Output Switching Slope Duration
(1)
Output Switching Slope Duration
(1)
Output Switching Slope Duration
(1)
Locked Rotor Period
Locked Rotor Period
Locked Rotor Period
Locked Rotor Period
Thermal Protection Shutdown
Thermal Protection Release
Symbol
V
DD
I
DD
R
DSON 1,2
V
OUT 1,2
V
OL
V
CLMP
I
LEAK
I
FGLIM
T
SW
T
SW
T
SW
T
SW
T
ON
T
OFF
T
ON
T
OFF
T
SD
T
REL
Test Conditions
Operating
Min
3
Typ
12
3
3
0.35
18
V
FG
(V
RD
) = 5V
V
FG
(V
RD
) = 12V
V
DD =
12V,
pin SLOPE left open
V
DD
= 12V,
R
SLOPE
=100k
V
DD
= 5V,
pin SLOPE left open
V
DD
= 5V,
R
SLOPE
=100k
V
DD
= 12V
V
DD
= 12V
V
DD
= 5V
V
DD
= 5V
Note 2
Note 2
Single layer PCB
40
87
73
87
0.24
1.44
0.48
2.88
10
20
70
120
126
120
0.29
1.5
0.6
3.65
160
130
150
160
189
250
189
0.39
2.34
0.89
5.34
s
s
s
s
o
C
o
C
o
C/Watt
o
Max
18
5
5
0.5
36
I
OL
= 4mA
Units
V
mA
Ω
V
V
V
A
mA
s
s
s
s
DC Package Thermal Resistance
R
TH
Table 3: Electrical specifications
Note 1:
Measured with active load connected to the output, from 10% to 90% of the V
DD
voltage.
Note 2:
Guarantied by design
7 Magnetic Specifications
DC Operating Parameters T
J
= 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
-6
2
Typ
3
-3
6
Max
6
Units
mT
mT
mT
o
390109020902
Rev 002
Page 4 of 12
Preliminary Datasheet
Mar/07
US651 / US661
Two-Coil Low Noise Fan Driver
8 Output Behaviour vs Magnetic Pole
Parameter
Test Conditions
North pole
B < Brp
South pole
B > Bop
Table 5: Driver output vs magnetic pole
OUT1
Low
High
OUT2
High
Low
FG
Low
High
Note :
The magnetic pole is applied facing the branded side of the package
9 Detailed General Description
The US651/661 is a one-chip solution for driving two-coil brushless DC fans. Based on CMOS process, the
chip contains a Hall-effect sensor with dynamic offset correction, logic control and two low-ohmic open-drain
output drivers.
The output drivers OUT1 and OUT2 are fully protected against switching transients. So there is no need of
external zener diode to cut the high voltage spikes induced by the fan coils.
In case the junction temperature T
J
exceeds T
SD
, the thermal protection stops the current flowing through the
full bridge by setting the outputs OUT1 and OUT2 low and setting the output FG (RD) high.
The IC stays in this state until the junction temperature decreases below T
REL
.
Reverse voltage protection is integrated on the V
DD
pin.
The FG/RD open drain output has an internal current limit which protects the driver in case of accidentally big
current flow through the logic driver. It could occur if a low-ohmic pull-up resistor is used or if the FG/RD
output is directly short connected to a supply voltage.
The US651 has an open-drain tachometer FG output that follows the Hall signal, thus enabling to determine
the rotation speed of the fan.
In the US661, 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:
- 2Hz for 12V application (60RPM for 2 pole-pair fan)
- 1Hz for 5V application (30RPM for 2 pole-pair fan)
390109020902
Rev 002
Page 5 of 12
Preliminary Datasheet
Mar/07
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