A4931 Datasheet

A4931
3-Phase Brushless DC Motor Pre-Driver
Features and Benefits
Description
▪ Drives 6 N-channel MOSFETs
▪ Synchronous rectification for low power dissipation
▪ Internal UVLO and thermal shutdown circuitry
▪ Hall element inputs
▪ PWM current limiting
▪ Dead time protection
▪ FG outputs
▪ Standby mode
▪ Lock detect protection
▪ Overvoltage protection
The A4931 is a complete 3-phase brushless DC motor pre-driver.
The device is capable of driving a wide range of N-channel
power MOSFETs and can support motor supply voltages up to
30 V. Commutation logic is determined by three Hall-element
inputs spaced at 120°.
Other features include fixed off-time pulse width modulation
(PWM) current control for limiting inrush current, locked-rotor
protection with adjustable delay, thermal shutdown, overvoltage
monitor, and synchronous rectification. Internal synchronous
rectification reduces power dissipation by turning on the
appropriate MOSFETs during current decay, thus shorting
the body diode with the low RDS(on) MOSFET. Overvoltage
protection disables synchronous rectification when the motor
pumps the supply voltage beyond the overvoltage threshold
during current recirculation.
Package: 28-contact QFN (ET package)
The A4931 offers enable, direction, and brake inputs that can
control current using either phase or enable chopping. Logic
outputs FG1 and FG2 can be used to accurately measure motor
rotation. Output signals toggle state during Hall transitions,
providing an accurate speed output to a microcontroller or
speed control circuit.
Approximate Scale 1:1
Operating temperature range is –20°C to 105°C. The A4931
is supplied in a 5 mm × 5 mm, 28-terminal QFN package with
exposed thermal pad. This small footprint package is lead (Pb)
free with 100% matte tin leadframe plating.
Typical Application
0.1 μF
0.1 μF
0.1 μF 2 kΩ
VIN
CLD HBIAS
CP1
CP2 VCP VBB
VIN
GHA
SA
GLA
M
FG1
A4931
System
Control
Logic
FG2
BRAKEZ
ENABLE
DIR
GHB
SB
GLB
GHC
SC
GLC
SENSE
GND HA+ HA– HB+ HB– HC+ HC–
4931-DS, Rev. 6
0.1 μF
A4931
3-Phase Brushless DC Motor Pre-Driver
Selection Guide
Part Number
A4931METTR-T
Packing
Package
1500 pieces per reel
5 mm x 5 mm, 0.90 mm nominal height QFN
Absolute Maximum Ratings
Characteristic
Load Supply Voltage
Symbol
Notes
VBB
Motor Phase Output
SX
tw < 500 ns
Hall Input
VHx
DC
Logic Input Voltage Range
VIN
Units
38
V
–3
V
–0.3 to 7
V
–0.3 to 7
V
Operating Ambient Temperature
TA
–20 to 105
ºC
Maximum Junction Temperature
TJ(max)
150
ºC
Tstg
–40 to 150
ºC
Rating
Units
32
ºC/W
2
ºC/W
Storage Temperature
Range M
Rating
Thermal Characteristics
Characteristic
Symbol
Package Thermal Resistance, Junction
RθJA
to Ambient
Package Thermal Resistance, Junction
RθJP
to Exposed Pad
*For additional information, refer to the Allegro website.
Test Conditions*
4-layer PCB based on JEDEC standard
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4931
3-Phase Brushless DC Motor Pre-Driver
Functional Block Diagram
0.1 μF
CLD
Lock
Detect
CP1
CP2
0.1 μF
FG1
VCP
CHARGE PUMP
0.1 μF
HBIAS
2 kΩ
HA+
HALL
HA-
HB+
HALL
VIN
Enable
0.1 μF
VBB
VREG
OVP
VCP
Communication
Logic
VREG
GHA
SA
HB-
GHB
SB
GLB
GATE
DRIVE
HC+
HALL
HC-
GHC
SC
GLC
Control
Logic
FG1
FG2
GLA
BRAKEZ
SENSE
System
Logic
DIR
RSENSE
200 mV
ENABLE
VIN
GND
Terminal List
Number
Name
1
HA+
2
HA -
3
4
5
6
Description
Number
Name
Description
Hall input A
15
GLB
Low side gate drive B
Hall input A
16
GLA
Low side gate drive A
HB+
Hall input B
17
GHC
High side gate drive C
HB -
Hall input B
18
SC
HC+
Hall input C
19
GHB
HC-
Hall input C
20
SB
7
GND
Ground
21
GHA
8
HBIAS
Hall bias power supply output
22
SA
9
CP1
Charge pump capacitor terminal
23
FG1
10
CP2
Charge pump capacitor terminal
24
FG2
FG 2 speed control output (ΦA input)
11
VBB
Supply voltage
25
CLD
Locked rotor detect timing capacitor
12
VCP
Reservoir capacitor terminal
26
DIR
13
SENSE
Sense resistor connection
27
ENABLE
Logic input – external PWM control
14
GLC
Low side gate drive C
28
BRAKEZ
Logic input – motor brake (active low)
High side source connection C
High side gate drive B
High side source connection B
High side gate drive A
High side source connection A
FG 1 speed control output (3 Φ inputs)
Logic input – motor direction
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4931
3-Phase Brushless DC Motor Pre-Driver
ELECTRICAL CHARACTERISTICS* Valid at TA= 25°C, VBB = 24 V, unless noted otherwise
Characteristics
Supply Voltage Range
Motor Supply Current
Symbol
VBB
IBB
Test Conditions
Min.
Typ.
Max.
Operating
8
–
VBBOV
V
fPWM < 30 kHz, CLOAD = 1000 pF
–
5
6
mA
–
3
3.5
mA
7.2
7.5
7.8
V
IHBIASlim
30
–
–
mA
VIN(1)
2
–
–
V
VIN(0)
–
–
0.8
V
HBIAS
VHBIAS
HBIAS Current Limit
Charge pump on, outputs disabled, Standby mode
Units
0 mA ≤ IHBIAS ≤ 24 mA
Control Logic
Logic Input Voltage
Logic Input Current
Input Pin Glitch Reject
IIN(1)
VIN = 2 V
–1
<1.0
1
μA
IIN(0)
VIN = 0.8 V
–1
<–1.0
1
μA
ENB pin
350
500
650
ns
DIR, BRAKEZ pins
700
1000
1300
ns
To outputs off
2.1
3
3.9
ms
tGLITCH
ENB Standby Pulse Propagation Delay
tdENB
HBIAS Wake-up Delay, Standby Mode
tdHBIAS
CHBIAS = 0.1 μF
–
15
25
μs
High-Side Gate Drive Output
VGS(H)
Relative to VBB, IGATE = 2 mA
7
–
–
V
Low-Side Gate Drive Output
VGS(L)
IGATE = 2 mA
7
–
–
V
Gate Drive
Gate Drive Current (Sourcing)
IGate
20
30
–
mA
Gate Drive Pull Down Resistance
RGate
GH = GL = 4 V
10
28
40
Ω
Dead Time
tdead
700
1000
1300
ns
Current Limit Input Threshold
VREF
180
200
220
mV
Fixed Off-Time
tOFF
18
25
37
μs
TJTSD
155
170
185
°C
Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
TJTSDhys
VBB UVLO Enable Threshold
VBBUV
VBB UVLO Hysteresis
VCP UVLO
Lock Detect Duration
VBB Overvoltage Threshold
Rising VBB
14
15
26
°C
6.2
7
7.85
V
0.4
0.75
1
V
Relative to VBB
4.6
–
6
V
tlock
C = 0.1 μF
1.5
2
2.5
s
VBBOV
Rising VBB
30
33
37.5
V
VIN = 0.2 to 3.5 V
–1
0
1
μA
VBBUVhys
VCPUV
Hall Logic
Hall Input Current
IHALL
Common Mode Input Range
VCMR
0.2
–
3.5
V
AC Input Voltage Range
VHALL
60
–
–
mVp-p
Difference between Hall inputs at transitions
–
+10,–10
–
mV
TJ = 25°C
10
20
30
mV
TJ = –20°C to 125°C
5
20
40
mV
–
2
–
μs
Hall Thresholds
Vth
Hall Threshold Hysteresis
VHYS
Pulse Reject Filter
tpulse
FG
FG Output Saturation Voltage
FG Leakage Current
VFG(sat)
IFG = 2 mA
–
–
0.5
V
IFGlkg
VFG = 5 V
–
–
1
μA
*Typical data are for initial design estimations only, and assume optimum manufacturing and application conditions. Performance may vary for
individual units, within the specified maximum and minimum limits.
For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
Specifications throughout the allowed operating temperature range are guaranteed by design and characterization.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4931
3-Phase Brushless DC Motor Pre-Driver
Logic States Table (See timing charts, below) X = Don’t Care, Z = high impedance
Inputs
Condition
DIR = 1
(Forward)
Resulting Pre-Driver Outputs
HA
HB
HC
BRAKEZ
ENB
A
+
–
+
HI
LO
Motor Output
GHA GLA GHB GLB GHC GLC
HI
LO
LO
HI
LO
A
B
C
LO
HI
LO
Z
B
+
–
–
HI
LO
HI
LO
LO
LO
LO
HI
HI
Z
LO
C
+
+
–
HI
LO
LO
LO
HI
LO
LO
HI
Z
HI
LO
D
–
+
–
HI
LO
LO
HI
HI
LO
LO
LO
LO
HI
Z
E
–
+
+
HI
LO
LO
HI
LO
LO
HI
LO
LO
Z
HI
F
–
–
+
HI
LO
LO
LO
LO
HI
HI
LO
Z
LO
HI
A
+
–
+
HI
LO
LO
HI
HI
LO
LO
LO
LO
HI
Z
F
–
–
+
HI
LO
LO
LO
HI
LO
LO
HI
Z
HI
LO
E
–
+
+
HI
LO
HI
LO
LO
LO
LO
HI
HI
Z
LO
D
–
+
–
HI
LO
HI
LO
LO
HI
LO
LO
HI
LO
Z
C
+
+
–
HI
LO
LO
LO
LO
HI
HI
LO
Z
LO
HI
B
+
–
–
HI
LO
LO
HI
LO
LO
HI
LO
LO
Z
HI
Fault*
+
+
+
HI
X
LO
LO
LO
LO
LO
LO
Z
Z
Z
Fault*
–
–
–
HI
X
LO
LO
LO
LO
LO
LO
Z
Z
Z
Brake*
X
X
X
LO
X
LO
HI
LO
HI
LO
HI
LO
LO
LO
DIR = 0
(Reverse)
* DIR = Don’t Care
DIR = 1 = FOR
A
B
C
D
DIR = 0 = REV
E
A
F
HA
HA
HB
HB
HC
HC
FG1
FG1
SA
SA
SB
SB
SC
SC
F
E
D
C
B
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
A4931
3-Phase Brushless DC Motor Pre-Driver
Power-up and Standby Modes Timing Diagram
VBB
VBBUV
Charge
Pump
HBIAS
Voltage
tdENB 3 ms
Standby Mode
Turn off Hall
Bias Supply
ENB
Outputs Enabled
Outputs Disabled
Outputs Enabled
Power-up and Standby Modes Timing Diagram
VBB
VBBUV
VBB+7.5 V
VCPUV
Charge
Pump
7.5V
VHBIAS
HBIAS
Voltage
ENB
PWM
Outputs Enabled
Outputs Disabled
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
A4931
3-Phase Brushless DC Motor Pre-Driver
Functional Description
Current Regulation Load current is regulated by an internal
fixed off-time PWM control circuit. When the outputs of the full
bridge are turned on, current increases in the motor winding until
it reaches a value, ITRIP , given by:
ITRIP = 200 mV / RSENSE
pletes, in order to provide the blanking function. The blanking
timer is reset when ENB is chopped or DIR is changed. With
external PWM control, a DIR change or an ENB on triggers the
blanking function. The duration is fixed at 1.5 μs.
Synchronous Rectification When a PWM-off cycle is
.
When ITRIP is reached, the sense comparator resets the source
enable latch, turning off the source driver. At this point, load
inductance causes the current to recirculate for the fixed off-time
period.
Enable Logic The Enable input terminal (ENB pin) allows
external PWM. ENB low turns on the selected sink-source pair.
ENB high switches off the appropriate drivers and the load
current decays. If ENB is held low, the current will rise until it
reaches the level set by the internal current control circuit. Typically PWM frequency is in 20 kHz to 30 kHz range. If the ENB
high pulse width exceeds 3 ms, the gate outputs are disabled. The
Enable logic is summarized in the following table:
ENB Pin Setting
Outputs
Outputs State
0
On
Drive
1
Source Chopped
Slow Decay with
Synchronous
Rectification
1 for > 3 ms typical
Off
Disable
Fixed Off-Time The A4931 fixed off-time is set to 25 μs
nominal.
PWM Blank Timer When a source driver turns on, a current
spike occurs due to the reverse recovery currents of the clamp
diodes as well as switching transients related to distributed
capacitance in the load. To prevent this current spike from erroneously resetting the source Enable latch, the sense comparator is
blanked. The blanking timer runs after the off-time counter com-
triggered, either by a chop command on ENB or by an internal
fixed off-time cycle, load current recirculates. The A4931 synchronous rectification feature turns on the appropriate MOSFETs
during the current decay, and effectively shorts out the body
diodes with the low RDS(on) driver. This lowers power dissipation
significantly and can eliminate the need for external Schottky
diodes.
Brake Mode A logic low on the BRAKEZ pin activates Brake
mode. A logic high allows normal operation. Braking turns on all
three sink drivers, effectively shorting out the motor-generated
BEMF. The BRAKEZ input overrides the ENB input and also the
Lock Detect function.
It is important to note that the internal PWM current control circuit does not limit the current when braking, because the current
does not flow through the sense resistor. The maximum current
can be approximated by VBEMF / RLOAD. Care should be taken to
insure that the maximum ratings of the A4391 are not exceeded
in the worse case braking situation, high speed and high inertial
load.
HBIAS Function This function provides a power supply of
7.5 V, current-limited to 30 mA. This reference voltage is used to
power the logic sections of the IC and also to power the external
Hall elements.
Standby Mode To prevent excessive power dissipation due
to the current draw of the external Hall elements, Standby mode
turns off the HBIAS output voltage. Standby mode is triggered
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
A4931
3-Phase Brushless DC Motor Pre-Driver
by holding ENB high for longer than 3 ms. Note that Brake mode
overrides Standby mode, so hold the BRAKEZ pin high in order
to enter Standby mode.
Lock Detect Function The IC will evaluate a locked rotor
Charge Pump The internal charge pump is used to generate a
• The proper commutation sequence is not being followed. The
motor can be locked in a condition in which it toggles between
two specific Hall device states.
supply above VBB to drive the high-side MOSFETs. The voltage on the VCP pin is internally monitored, and in case of a fault
condition, the outputs of the device are disabled.
Fault Shutdown In the event of a fault due to excessive
junction temperature or due to low voltage on VCP or VBB,
the outputs of the device are disabled until the fault condition is
removed. At power-up the UVLO circuit disables the drivers.
condition under either of these two different conditions:
• The FG1 signal is not consistently changing.
Both of these fault conditions are allowed to persist for period
of time, tlock. tlock is set by capacitor connected to CLD pin. CLD
produces a triangle waveform (1.67 V peak-to-peak) with frequency linearly related to the capacitor value. tlock is defined as
127 cycles of this triangle waveform, or:
Overvoltage Protection VBB is monitored to determine if
tlock = CLD × 20 s/μF
a hazardous voltage is present due to the motor generator pumping up the supply bus. When the voltage exceeds VBBOV , the
synchronous rectification feature is disabled.
After the wait time, tlock , has expired, the outputs are disabled,
and the fault is latched. These fault conditions can only be cleared
by any one of the following actions:
Overtemperature Protection If die temperature exceeds
• Rising or falling edge on the DIR pin
approximately 170°C, the Thermal Shutdown function will disable the outputs until the internal temperature falls below the
15°C hysteresis.
Hall State Reporting The FG1 pin is an open drain output
that changes state at each transition of an external Hall element.
The FG2 pin is an open drain output that changes state at each
HAx transition.
• VBB UVLO threshold exceeded (during power-up cycle)
• ENB pin held high for > tlock / 2
The Lock Detect function can be disabled by connecting CLD to
GND.
When the A4931 is in Brake mode, the Lock Detect counter is
disabled.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A4931
3-Phase Brushless DC Motor Pre-Driver
ET Package, 28-Contact QFN
0.30
5.00 ±0.15
1.15
28
1
2
0.50
28
1
A
5.00 ±0.15
3.15
4.80
3.15
29X
D
SEATING
PLANE
0.08 C
C
4.80
C
+0.05
0.25 –0.07
PCB Layout Reference View
0.90 ±0.10
0.50
For Reference Only
(reference JEDEC MO-220VHHD-1)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
+0.20
0.55 –0.10
A Terminal #1 mark area
B
3.15
2
1
28
3.15
B Exposed thermal pad (reference only, terminal #1
identifier appearance at supplier discretion)
C Reference land pattern layout (reference IPC7351
QFN50P500X500X100-29V1M);
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)
D Coplanarity includes exposed thermal pad and terminals
Copyright ©2007-2013, Allegro MicroSystems, LLC
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.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
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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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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