A4941 Datasheet PDF - Allegro Micro Systems
| Part Number | A4941 | |
| Description | Three-Phase Sensorless Fan Driver | |
| Manufacturers | Allegro Micro Systems | |
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A4941
Three-Phase Sensorless Fan Driver
Features and Benefits
• 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
Package: 16-pin TSSOP with exposed
thermal pad (suffix LP)
Description
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.
Not to scale
12 V
10 μF
VBB
SLEW
PWM
25 kHz
VBB
O/C FC
TEST
10 kΩ
FG
Functional Block Diagram
VCP
0.1 μF
CP1
0.1 μF
CP2
+VINT
Soft
Switch
Control
Logic
Charge
Pump
3-Phase
Half Bridges
OUTA
OUTB
OUTC
M
OSC
Timers
Startup
OSC
Sequencer
(Direction)
CDCOM
Adaptive
Commutation
Delay
FCOM
OCP
SENSE
0.167 Ω
GND
OUTA
OUTB
OUTC
CTAP
GND
BEMF Comparator
A4941-DS, Rev. 4
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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.
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.
Standby Mode
Driving PWM low for 500 μs causes the IC to enter a low power
standby mode.
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 pulled-
up to logic high level.
• 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 mini-
mum 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.
SLEW Input
Enables or disables soft switching by connection as follows:
SLEW Pin Connection
GND
Open
Soft Start Status
Enabled
Disabled
FC Input
This is the logic input to set force commutation time at startup, by
connection as follows:
FC Pin Connection
GND
VBB
Open
Startup Commutation Time
(ms)
100
50
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
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for A4941 electronic component. |
| Information | Total 9 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ A4941.PDF Datasheet ] | |
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