US72/73
Single Coil Fan Driver
Features and Benefits
Full Bridge Driver
High Sensitivity Hall Sensor
Locked Rotor Shutdown and Auto-Restart
Power-Efficient CMOS and Power MOSFETs
Integrated tachometer (US72) or alarm (US73) signal outputs
Applications
For 12V/24V Fans
Ordering Information
Part No.
US72
US73
Temperature Suffix
E (-40° to 85°
C
C)
E (-40° to 85°
C
C)
Package Code
DC (8-Pin narrow SOIC)
DC (8-Pin narrow SOIC)
Functional Diagram
Out1
3
Out2
6
Vdd
1
Regulator
Clamp
8
Description
The US72 and US73 provide a monolithic
solution for driving single-coil fans. The bridge
drivers provide bi-directional current through the
single phase motor winding.
US72: The tachometer/Frequency Generator
(FG) version produces a logic signal, which is
aligned with the Hall plate signal.
US73: The Rotation Detector (RD) / Alarm
Signal version has a low output in the normal
condition. When a locked rotor condition occurs
the RD changes to a high state.
P1
Hall
Amp.
P2
Gate Drive
Switching
Logic
Gate Drive
2
FG/RD
N1
Locked-Rotor
Protection
N2
Gnd
4
7
5
3901090261
Rev. 002
Page 1 of 9
Data Sheet
May/04
US72/73
Single Coil Fan Driver
TABLE OF CONTENTS
FEATURES AND BENEFITS ................................................................................................................ 1
APPLICATIONS .................................................................................................................................... 1
ORDERING INFORMATION ................................................................................................................. 1
FUNCTIONAL DIAGRAM................................................................................................................... 1-1
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
GLOSSARY OF TERMS............................................................................................................. 3
ABSOLUTE MAXIMUM RATINGS............................................................................................. 3
US72/73 ELECTRICAL SPECIFICATIONS ............................................................................... 3
US72/73 MAGNETIC SPECIFICATIONS................................................................................... 4
GENERAL DESCRIPTION ......................................................................................................... 4
UNIQUE FEATURES .................................................................................................................. 4
PERFORMANCE GRAPHS........................................................................................................ 5
APPLICATIONS INFORMATION ............................................................................................... 6
APPLICATION COMMENTS...................................................................................................... 6
RELIABILITY INFORMATION.................................................................................................... 7
ESD PRECAUTIONS.................................................................................................................. 7
DC PACKAGE INFORMATION (SOIC-8) .................................................................................. 8
DISCLAIMER .............................................................................................................................. 9
3901090261
Rev. 002
Page 1-2 of 9
Data Sheet
May/04
US72/73
Single Coil Fan Driver
1. Glossary of Terms
Full Bridge: Two output drivers that can both source or sink current. When a load is placed between the
drivers, current can flow through the load in both directions.
FG: The Frequency Generator or tachometer signal; provides one pulse for every magnetic pole
RD: The Rotation detection or Lock Alarm signal is high when the rotor is blocked or spinning very slowly.
MilliTesla (mT), Gauss: Units of magnetic flux density; 1 milliTesla = 10 Gauss
Single Coil Fan: a fan with only one coil winding, usually requiring a bipolar or full-bridge driver
Locked rotor: The condition of a fan that has stopped spinning due to mechanical blockage
2. Absolute Maximum Ratings
Supply Voltage, V
DD
(overvoltage)
Output Voltage, FG or RD
Output Current, I
OUT
Operating Temperature Range, T
A
Junction Temperature, T
j
Storage Temperature, T
s
ESD Sensitivity (AEC Q100 002)
Magnetic Flux Density
28V
28V
500mA
-40 to 85°C
125°C
-55 to 150°C
2KV
No limit
Exceeding the absolute maximum ratings may cause permanent damage. Exposure to absolute-
maximum-rated conditions for extended periods may affect device reliability.
3. US72/73 Electrical Specifications
DC Operating Parameters T
A
= 25 C, V
DD
= 12V (unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
o
Max
Units
Supply Voltage
Supply Current
On Resistance
Bridge Current
Bridge Current
Thermal Resistance
Locked-Rotor Period
Locked-Rotor period
Freewheel Switching delay
FG/RD Output Leakage
FG/RD On voltage
V
DD
I
DD
R
dson
I
load
I
load
R
th
t
on
t
off
t
fw
I
off
V
dson
Operating
V
DD =
24V, No Load
Full bridge, R
nmos
+ R
pmos
Peak
Continuous
one-sided PCB, zero LFPM
4.5
4
3
28
6
5.3
500
350
150
0.25
1.25
200
Volts
mA
Ohms
mA
mA
o
C/Watt
S
S
uS
10
0.5
uA
Volts
V
out
= 24V
Iout = 5mA
3901090261
Rev. 002
Page 3 of 9
Data Sheet
May/04
US72/73
Single Coil Fan Driver
4. US72/73 Magnetic Specifications
DC Operating Parameters T
A
= 25, T
A
= 25 C, V
DD
= 12V (unless otherwise specified)
Parameter
Operate Point
Release Point
Hysteresis
Symbol
Bop
Brp
Hys
-6.0
Test Conditions
Min
Typ
3.0
-3.0
6.0
Max
6.0
Units
mT
mT
mT
o
Note:
1 mT = 10 Gauss
5. General Description
The US72 / US73 provide a one-chip solution for 2-wire or 3-wire fans with a single coil winding. The chip
contains the Hall-effect sensor, dynamic offset correction, and power drivers in a single package. The
output drivers and supply pins are fully protected against switching transients. The FG or RD open-drain
signal outputs are compatible with any TTL or CMOS logic input.
6. Unique Features
The switching of the load current is controlled to limit current slew-rate, and eliminate shoot-through
currents. The 200uS (typical) recirculation allows the current to decay, reducing the switching noise.
The built-in locked-rotor protection will automatically shut off the coil current when the rotor is
mechanically blocked, or the rotational speed drops below 60 RPM. The fan will try to restart every 1.5
seconds until the obstruction is clear. The On / Off cycling reduces the average stall current to 1/6
normal; this is enough to prevent overheating or damage to most fans.
A common two-coil fan with unipolar drivers only uses half of the coil windings at any time. The one-coil
design with full-bridge drivers uses all the windings all the time to generate torque. This generally allows
for a smaller, more efficient stator design.
3901090261
Rev. 002
Page 4 of 9
Data Sheet
May/04
US72/73
Single Coil Fan Driver
7. Performance Graphs
Rdson (NMOS + PMOS)
vs.
Vdd, Temperature
US72 / 73
10
8
Rdson (Ohms)
Rdson (Ohms)
10
8
Rdson (NMOS + PMOS)
vs.
Vdd, Temperature
US72 / 73
4V
6
4
2
0
-40
5V
12 V
30 V
6
4
125
25
2
0
0
40
80
120
4
8
12
16
20
24
28
Junction Tem perature (C)
Vdd Voltage (V)
Bop, Brp
vs.
Temperature
5
Bop
3
Bop, Brp (mT)
US72 / 73
Bop, Brp
vs.
Vdd Voltage
US72 / 73
5
Bop
3
Bop, Brp (mT)
1
-1
Brp
-3
-5
1
-1
Brp
-3
-5
-40
0
40
80
120
0
10
20
30
Junction Temperature (C)
Vdd (Volts)
3901090261
Rev. 002
Page 5 of 9
Data Sheet
May/04
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