US90A / US91A
24V Hall IC Fan Driver
Features and Benefits
Low cost
12V/24V fans
High sensitivity Hall Sensor
Peak current up to 500mA
Application Examples
Locked rotor protection and auto-restart
Power-efficient CMOS and power MOSFETs
Built-in output protection clamping diode
Integrated tachometer (US90A) or alarm (US91A)
signal output
2-coil fan driver with FG/RD output in 4-pin VK / VA
and 8-pin narrow SOIC packages (all RoHS
Compliant
Ordering Code
Product Code
Temperature Code
Package Code
Option Code
Packing Form Code
US90A
US90A
US91A
US90A
US90A
US91A
US91A
US90A
US91A
Legend:
Package Code:
E
E
E
E
E
E
E
E
E
DC
DC
DC
VK
VK
VK
VK
VA
VA
AAA-000
AAA-000
AAA-000
AAA-000
AAA-000
AAA-000
AAA-000
AAA-000
AAA-000
RE
RX
RX
BU
RX
BU
RX
BU
BU
o
o
o
Packing Form:
o
o
o
DC for SOIC150Mil,
VK for
Plastic Single in Line thickness 1.5 - 1.6mm
VA for
Plastic Single in Line thickness 1.1 -1.2mm
RE for Reel (face up, live bug)
RX for Reel (face down, dead bug)
VKAAA000-RX: Trimmed leads: 5.17mm
BU for Bulk
Ordering example:
US90A-EDC-AAA-000-RE
1 Functional Diagram
2 General Description
The US90A/91A is a one-chip solution for driving two-
coil brushless DC cooling fans.
Based on the advanced Melexis CMOS process, the IC
contains a Hall-effect sensor, dynamic offset correction
and low side output drivers.
Frequency Generator or Rotation Detection is available.
The open-drain output makes the connectivity with any
external interface such as hardware monitoring or
Super I/O IC easier.
These features are combined with the Melexis patented
no-V
DD
design to fit the IC in small 4-pin VK and VA
package. The device is also delivered in DC package
for automatic assembly.
3901090263
Rev 008
Page 1 of 12
Data Sheet
Jan/14
US90A / US91A
24V Hall IC Fan Driver
3 Glossary of terms
Two-coil fan
MilliTesla (mT), Gauss
V
DD
I
DD
Peak output current
Continuous output
current
Locked rotor
FG
RD
LFPM
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 coils common node.
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 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
Linear Feet Per Minute – Unit of airflow velocity
4 Absolute maximum rating
Parameter
Fan Supply Voltage
Peak Output Current
Continuous Output Current
FG / RD Output Current
Junction Temperature
Symbol
V
DD
I
OUTp
I
OUTc
I
FG (RD)
T
J
Value
30
500
250
20
-40 to 125
Units
V
mA
mA
mA
°C
Storage Temperature Range
T
S
-55 to 150
°C
Magnetic Flux Density
B
Unlimited
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
FG (RD)
OUT1
OUT2
GND
Pin number (VK)
1
2
3
4
Pin number (DC)
1
2
4
3
5, 6, 7, 8
Pin number (VA)
1
2
4
3
Function
FG (RD) open drain output
signal
Open Drain Coil Driver 1
Open Drain Coil Driver 2
Ground pin
Not Connected
Table 2: Pin definitions and descriptions US90A (US91A)
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Data Sheet
Jan/14
US90A / US91A
24V Hall IC Fan Driver
6 General electrical specifications
o
DC Operating Parameters T
A
= 25 C, V
DD
= 24V (unless otherwise specified)
Symbo
l
V
DD
I
DD
V
DSON
1,2
Parameter
Fan Supply Voltage
Supply Current
Output Saturation Voltage
Output Saturation Voltage
Output Clamp Voltage
FG / RD Output Low
Voltage
FG / RD Output Clamp
Voltage
FG / RD Output Leakage
Current
DC Thermal Resistance
VK Thermal Resistance
VA Thermal Resistance
Test Conditions
Operating, R
COIL
= 50Ω
I
OUT
= 150mA
I
OUT
= 250mA
Min
4.7
(1)
Typ
Max
30
Units
V
mA
mV
mV
V
2
375
625
60
I
OL
= 10mA
28
V
FG
(V
RD
) = 18V
Onesided PCB, zero LFPM
Onesided PCB, zero LFPM
Onesided PCB, zero LFPM
150
200
170
250
4
V
DSON
1,2
V
OUT 1,2
V
OL
V
CLAMP
I
LEAK
R
THja
R
THja
R
THja
500
mV
V
10
uA
°C/Watt
°C/Watt
°C/Watt
Table 3: General electrical specifications
Note 1:
The minimal value of VDD should be determined using the following equation: V
DD
= 4.5V + R
COIL
* I
DD
7 Magnetic specifications
o
DC Operating Parameters T
A
= 25 C, V
DD
= 24V (unless otherwise specified)
Parameter
Operate point
Release point
Hysteresis
Symbol
B
OP
B
RP
B
HYST
Test Conditions
Min
6
2
Typ
3
3
6
Max
6
Units
mT
mT
mT
Table 4: Magnetic specifications
8 Driver output vs. Magnetic Pole
Parameter
North pole
South pole
Test Conditions
B < Brp – all packages
B > Bop all packages
OUT1
High
Low
OUT2
Low
High
Table 5: Driver output vs. magnetic pole
Note 3:
The magnetic pole is applied facing the branded side of the package
3901090263
Rev 008
Page 3 of 12
Data Sheet
Jan/14
US90A / US91A
24V Hall IC Fan Driver
9 Detailed general description
The US90A/91A is a one-chip solution for driving two-coil brushless DC fans. Based on advanced Melexis CMOS
process, the IC contains a Hall-effect sensor, dynamic offset correction and low side output drivers.
The output drivers OUT1 and OUT2 are fully protected against switching transients. So there is no need for an external
zener diode to cut the high voltage spikes induced by the fan coils.
The US90A has an open-drain integrated tachometer FG output that follows the Hall signal. In the US91A, 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
The absence of a V
DD
pin enables the two low side output drivers and FG/RD signal output to fit in a four-pin VK package.
The lack of a V
DD
pin decreases also the probability to damage the chip due to reverse voltage connection, using the coil
resistance to limit the reverse current. In this condition, the total reverse current is twice the peak current value of the fan
used.
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 (4-pole rotor magnet). 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 1/7 normal; this is
enough to prevent overheating or damage to most fans. Both the US90A and US91A have this feature.
3901090263
Rev 008
Page 4 of 12
Data Sheet
Jan/14
US90A / US91A
24V Hall IC Fan Driver
11 Performance Graphs
11.1 R
DSON
vs T
J
11.2 R
DSON
vs V
DD
11.3 Magnetic parameters vs T
J
11.4 Magnetic parameters vs V
DD
11.5 I
DD
vs T
J
11.6 I
DD
vs V
DD
11.7 V
OL
vs T
J
11.8 Power Dissipation vs. T
A
3901090263
Rev 008
Page 5 of 12
Data Sheet
Jan/14
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