A4941 Datasheet

A4941
Three-Phase Sensorless Fan Driver
Features and Benefits
Description
• Sensorless (no Hall sensors required)
• Soft switching for reduced audible noise
• Minimal external components
• PWM speed input
• FG speed output
• Low power standby mode
• Lock detection
• Optional overcurrent protection
• Variant A automotive qualified to AEC-Q100 Grade 2
The A4941 three-phase motor driver incorporates BEMF
sensing to eliminate the requirement for Hall sensors in fan
applications.
A pulse wave modulated (PWM) input is provided to control
motor speed, allowing system cost savings by eliminating
external variable power supply. PWM input can also be used
as an on/off switch to disable motor operation and place the
IC into a low power standby mode.
The A4941 is provided in a 16-pin TSSOP package (suffix LP)
with an exposed thermal pad. It is lead (Pb) free, with 100%
matte tin leadframe plating.
Package: 16-pin TSSOP with exposed
thermal pad (suffix LP)
Not to scale
Functional Block Diagram
12 V
0.1 μF
VCP
0.1 μF
CP1
VBB
CP2
Charge
Pump
10 μF
+VINT
OUTA
SLEW
Soft
Switch
PWM
Control
Logic
3-Phase
Half Bridges
OUTB
M
OUTC
25 kHz
OSC
SENSE
OCP
Timers
VBB
0.167 Ω
TEST
Sequencer
(Direction)
Startup
OSC
CTAP
CDCOM
Adaptive
Commutation
Delay
+
FG
FCOM
+
–
BEMF Comparator
A4941-DS, Rev. 4
OUTA
OUTB
–
10 kΩ
GND
–
FC
+
O/C
OUTC
GND
A4941
Three-Phase Sensorless Fan Driver
Selection Guide
Part Number
Application
A4941GLPTR-T
A4941GLPTR-A-T
Packing
Commerical/Industrial
Automotive
4000 pieces per 13-in. reel
4000 pieces per 13-in. reel
Absolute Maximum Ratings
Characteristic
Symbol
Supply Voltage
VBB
Logic Input Voltage Range
VIN
Logic Output Voltage
VOUT
Output Current
IOUT
Notes
Rating
Unit
20
V
PWM, SLEW
–0.3 to 5.5
V
FC
–0.3 to VBB
V
FG
VBB
V
Peak (startup and lock rotor)
1.25
A
r m s , duty cycle = 100%
900
mA
Operating Ambient Temperature
TA
–40 to 105
ºC
Maximum Junction Temperature
TJ(max)
150
ºC
Tstg
–55 to 150
ºC
Storage Temperature
G temperature range
Recommended Operating Conditions
Characteristic
Symbol
Supply Voltage
Conditions
Min.
VBB
Output Current
IOUT
Typ.
Max.
Unit
5
–
16
V
Peak (startup and lock rotor)
–
–
1
A
Run current
–
<500
–
mA
Value
Unit
On 4-layer PCB based on JEDEC standard
34
ºC/W
On 2-layer PCB with 1 in.2 of copper area each side
52
ºC/W
Thermal Characteristics may require derating at maximum conditions
Characteristic
Symbol
RθJA
Package Thermal Resistance
Test Conditions*
*Additional thermal information available on the Allegro website
Terminal List Table
Pin-out Diagram
OUTC 1
16 OUTB
CP1 2
15 OUTA
CP2 3
14 SENSE
VCP 4
GND 5
SLEW 6
PWM 7
FG 8
PAD
13 VBB
Name
Number
Function
CP1
2
Charge pump
CP2
3
Charge pump
CTAP
12
Motor terminal center tap
FC
10
Logic input
FG
8
GND
5, 11
Speed output signal
Ground
OUTA
15
Motor terminal A
OUTB
16
Motor terminal B
10 FC
OUTC
1
Motor terminal C
9 TEST
PWM
7
Logic input
SENSE
14
Sense resistor connection
SLEW
6
Logic input
TEST
9
Test use only, leave open circuit
VBB
13
Input supply
VCP
4
Charge pump
12 CTAP
11 GND
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4941
Three-Phase Sensorless Fan Driver
ELECTRICAL CHARACTERISTICS Valid at TJ = –40 to 105°C, VBB = 5 to 16 V*; unless otherwise noted
Characteristics
VBB Supply Current
Symbol
Test Conditions
IBB
IBBST
Min.
Typ.
Max.
Unit
–
2.5
5
mA
Standby mode, PWM = 0 V, SLEW = FC = O/C
–
25
50
μA
I = 800 mA, TJ = 25°C
–
800
1200
mΩ
VOCL
180
200
220
mV
VIL
–
–
0.8
V
PWM High Level
VIH
2
–
–
V
Input Hysteresis
VHYS
–
300
600
mV
Total Driver RDS(on) (Sink + Source)
Overcurrent Threshold
PWM Low Level
Logic Input Current
Output Saturation Voltage
FG Output Leakage
RDS(on)
IIN
PWM, VIN = 0 V
–25
–15
–5
μA
SLEW, VIN = 0 V
–70
–50
–20
μA
FC, VIN = 0 V
μA
–30
–15
–5
VSAT
I = 5 mA
–
–
0.3
V
IFG
V = 16 V
–
–
1
μA
1.6
2
2.4
s
Protection Circuitry
Lock Protection
Thermal Shutdown Temperature
ton
toff
4
5
6
s
150
165
180
°C
15
–
°C
4.3
4.7
V
TJTSD
Temperature increasing
Thermal Shutdown Hysteresis
TJHYS
Recovery = TJTSD – ∆TJ
–
VBB Undervoltage Lockout (UVLO)
VUVLO
VBB rising
–
*For the A4941GLPTR-T the electrical test is performed at 12 V only and characterized across the voltage range.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4941
Three-Phase Sensorless Fan Driver
Functional Description
The driver system is a three-phase, BEMF sensing motor controller and driver. Commutation is controlled by a proprietary BEMF
sensing technique.
The motor drive system consists of three half bridge NMOS
outputs, BEMF sensing circuits, adaptive commutation control,
and state sequencer. The sequencer determines which output
devices are active. The BEMF sensing circuits and adaptive commutation circuits determine when the state sequencer advances to
the next state.
A complete self-contained BEMF sensing commutation scheme is
provided. The three half-bridge outputs are controlled by a state
machine with six possible states, shown in figure 1. Motor BEMF
is sensed at the tri-stated output for each state.
BEMF sensing motor commutation relies on the accurate comparison of the voltage on the tri-stated output to the voltage at the
center tap of the motor. The BEMF zero crossing, the point where
the tri-stated motor winding voltage crosses the center tap voltage, is used as a positional reference. The zero crossing occurs
roughly halfway through one commutation cycle.
Output
State
A
B
C
D
E
Adaptive commutation circuitry and programmable timers
determine the optimal commutation points with minimal
external components. The major blocks within this system are:
the BEMF zero crossing detector, Commutation Delay timer, and
the Blank timer.
BEMF Zero Cross Detection
BEMF zero crossings are detected by comparing the voltage at
the tri-stated motor winding to the voltage at the motor center
tap. Zero crossings are indicated by the FCOM signal, which
goes high at each valid zero crossing and low at the beginning
of the next commutation. In each state, the BEMF detector looks
for the first correct polarity zero crossing and latches it until the
next state. This latching action, along with precise comparator
hysteresis, makes for a robust sensing system. At the beginning
of each commutation event, the BEMF detectors are inhibited for
a period of time set by the Blank timer. This is done so that commutation transients do not disturb the BEMF sensing system.
Commutation Event
See figure 1 for timing relationships. The commutation sequence
is started by a CDCOM pulse or a valid XCOM at startup. After
F
A
B
C
D
E
F
OUTA
OUTB
OUTC
FCOM
CDCOM
FG
Figure 1. Motor Terminal Output States
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4941
Three-Phase Sensorless Fan Driver
the commutation delay period, a CDCOM is asserted, starting
the Blank timer. The Blank signal disables the BEMF detector so
the comparator is not active during the commutation transients.
The next zero crossing, detected on the tri-stated output, causes
FCOM to go high. This triggers the Commutation Delay timer
and the sequence repeats.
CTAP
Connection pin for motor center-tap if available. If not available
(such as with delta type motors), the null point will be generated
internally.
• PWM also can be used as a control input to start and stop the
motor.
• For PWM applications, input frequencies in the range
15 to 30 kHz are applied directly to the motor windings. If the
PWM duty cycle is very small, then the IC will apply a minimum pulse width of typically 6 μs. This minimum pulse width
effects the minimum speed. As a result of having a minimum
pulse width, the IC can startup and operate down to very short
duty cycles.
Startup
At startup, commutations are provided by an onboard oscillator.
These commutations are part of the startup scheme, to step the
motor to generate BEMF until legitimate BEMF zero crossings
are detected and normal BEMF sensing commutation is achieved.
Until an appropriate number of FCOM pulses are achieved (96),
100% PWM will be applied to the motor windings.
SLEW Input
Enables or disables soft switching by connection as follows:
Standby Mode
Driving PWM low for 500 μs causes the IC to enter a low power
standby mode.
FC Input
This is the logic input to set force commutation time at startup, by
connection as follows:
Lock Detect
Valid FCOM signals must be detected to ensure the motor is not
stalled. If a valid FG is not detected for 2 s, the outputs will be
disabled for 5 s before an auto-restart is attempted.
FG Output
The FG output provides fan speed information to the system.
FG is an open drain output.
PWM Input
The duty cycle applied to the PWM pin is translated directly
to an average duty cycle applied across the motor windings
to control speed.
• For voltage controlled applications, where VBB controls the
speed, PWM can be left open circuit. PWM is internally pulledup to logic high level.
SLEW Pin Connection
Soft Start Status
GND
Enabled
Open
Disabled
FC Pin Connection
Startup Commutation Time
(ms)
GND
100
VBB
50
Open
200
Overcurrent Protection
If needed, a sense resistor can be installed to limit current. (See
Applications Information section for more details.) The current
limit trip point would be set by:
IOCL = 200 mV / RS .
When the trip point is reached, if the threshold voltage, VOCL , is
exceeded, the drivers will be disabled for 25 μs.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
A4941
Three-Phase Sensorless Fan Driver
Input/Output Structures
VBB
VCP
GND
CP1
GND
CP2
GND
100 kΩ
SLEW
250 kΩ
PWM
8V
GND
GND
GND
VBB
VBB
8V
VBB
OUTA
25 V
CTAP
MOS
Parasitic
OUTB
OUTC
GND
GND
GND
MOS
Parasitic
OUTA
OUTB
OUTC
GND
VBB
FC
FG
TEST
GND
8V
GND
GND
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
A4941
Three-Phase Sensorless Fan Driver
Application Information
M
Name
CTAP
VBB
C3
VBB
R2
C2
1 OUTC
2 CP1
3 CP2
4 VCP
5 GND
6 SLEW
7 PWM
8 FG
A4941
PAD
OUTB 16
OUTA 15
SENSE 14
VBB 13
R1
D1
C1
CTAP 12
CTAP
GND 11
FC 10
TEST 9
Typical Value
C1
10 μF / 25 V
C2,C3
0.1 μF / 25 V
Charge pump ceramic capacitors
R2
10 kΩ
D1
>1.5 A rated
D2
15 V
R1
0.167 Ω
D2
VBB
Typical Application Circuit; speed adjusted via VBB
Startup Oscillator Setting (FC)
Typically, the 50 ms setting is optimum for motors appropriate
for use with the A4941. If the motor does not produce a proper
BEMF signal at startup when power is applied, a longer setting
may be required.
SLEW Setting
Connect SLEW to ground to enable the soft switching function. For some motors, soft switching may reduce audible noise.
Enabling the soft switching function can result in motor stall for
some motors, specifically motors with large inductance that run at
higher speeds. For this situation, there are two potential solutions:
• Limit the motor speed by lowering the maximum demand, by
reducing either Vmotor(max) or the PWM duty applied.
• Disable soft switching by leaving SLEW pin open circuit.
Current Limiting
Use of the current limit circuit is not required. If motor resistance
(phase-to-phase) will limit the current below the rating in the
Description
VBB supply capacitor, minimum 10 μF,
electrolytic can be used
FG pull-up resistor, can be pulled-up to
VBB if required
Optional blocking diode for supply reverse
polarity protection
Transient voltage suppressor (TVS)
Current limiting sense resistor, required for
low resistance motors
Absolute Maximum table, then simply connect the SENSE pin to
ground. That is:
• If (VBB(max) / Rmotor ) < 1.25 A, eliminate RS.
• If (VBB(max) / Rmotor ) > IOUT (max), the choice of RS determines the current limit setting; recommended range is
167 mΩ < RS < 250 mΩ.
Note: For some motor types, use of the current limit circuit may
prevent proper startup due to the effect of the chopping on the
BEMF voltage appearing on the tri-stated winding.
Layout Notes
• Connect GND pins (5,11) to exposed pad ground area under
package.
• Add thermal vias from exposed pad to bottom side ground
plane.
• Place VBB decoupling capacitor as close to the IC as possible.
• Place sense resistor, (if used), as close to the IC as possible.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
A4941
Three-Phase Sensorless Fan Driver
Package LP, 16-Pin TSSOP with Exposed Thermal Pad
0.45
5.00±0.10
16
0.65
16
8º
0º
0.20
0.09
1.70
B
3 NOM
4.40±0.10
3.00
6.40±0.20
6.10
0.60 ±0.15
A
1
1.00 REF
2
3 NOM
0.25 BSC
Branded Face
16X
SEATING
PLANE
0.10 C
0.30
0.19
C
3.00
C
PCB Layout Reference View
For Reference Only; not for tooling use (reference MO-153 ABT)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
1.20 MAX
0.65 BSC
1 2
SEATING PLANE
GAUGE PLANE
0.15
0.00
A Terminal #1 mark area
B
Exposed thermal pad (bottom surface); dimensions may vary with device
C Reference land pattern layout (reference IPC7351
SOP65P640X110-17M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as
necessary to meet application process requirements and PCB layout
tolerances; when mounting on a multilayer PCB, thermal vias at the
exposed thermal pad land can improve thermal dissipation (reference
EIA/JEDEC Standard JESD51-5)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A4941
Three-Phase Sensorless Fan Driver
Revision History
Revision
Revision Date
Rev. 4
December 20, 2012
Description of Revision
Add information on CTAP, Automotive variant
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Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
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use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
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Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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