A3941 Datasheet

A3941
Automotive Full Bridge MOSFET Driver
Features and Benefits
Description
▪ High current gate drive for N-channel MOSFET full bridge
▪ High-side or low-side PWM switching
▪ Charge pump for low supply voltage operation
▪ Top-off charge pump for 100% PWM
▪ Cross-conduction protection with adjustable dead time
▪ 5.5 to 50 V supply voltage range
▪ Integrated 5 V regulator
▪ Diagnostics output
▪ Low current sleep mode
The A3941 is a full-bridge controller for use with external
N-channel power MOSFETs and is specifically designed for
automotive applications with high-power inductive loads, such
as brush DC motors.
Package: 28-pin TSSOP with exposed
thermal pad (suffix LP)
The full bridge can be driven in fast or slow decay modes using
diode or synchronous rectification. In the slow decay mode,
current recirculation can be through the high-side or the lowside FETs. The power FETs are protected from shoot-through
by resistor adjustable dead time.
A unique charge pump regulator provides full (>10 V) gate
drive for battery voltages down to 7 V and allows the A3941
to operate with a reduced gate drive, down to 5.5 V.
A bootstrap capacitor is used to provide the above-battery
supply voltage required for N-channel MOSFETs. An internal
charge pump for the high-side drive allows DC (100% duty
cycle) operation.
Integrated diagnostics provide indication of undervoltage,
overtemperature, and power bridge faults, and can be
configured to protect the power MOSFETs under most short
circuit conditions.
The A3941 is supplied in a 28-pin TSSOP power package with
an exposed thermal pad (suffix LP). This package is lead (Pb)
free, with 100% matte-tin leadframe plating.
Not to scale
Typical Application
VBAT
PWM
Direction
Fault Flags
3941-DS, Rev. 5
A3941
A3941
Automotive Full Bridge MOSFET Driver
Selection Guide
Part Number
A3941KLPTR-T
Packing
4000 pieces per reel
Absolute Maximum Ratings*
Characteristic
Load Supply Voltage
Symbol
Notes
VBB
Rating
Units
–0.3 to 50
V
–0.3 to 6.5
V
V5 Pin
–0.3 to 7
V
LSS Pin
–4 to 6.5
V
–0.3 to 6.5
V
SA and SB Pins
–5 to 55
V
VDRAIN Pin
–5 to 55
V
Logic Inputs and Outputs
VDSTH Pin
GHA and GHB Pins
Sx to Sx+15
V
GLA and GLB Pins
–5 to 16
V
CA and CB Pins
Operating Temperature Range
Junction Temperature
TA
–0.3 to Sx+15
V
–40 to 150
ºC
150
ºC
175
ºC
–55 to 150
ºC
Range K
TJ(max)
Transient Junction Temperature
TtJ
Storage Temperature Range
Tstg
Overtemperature event not exceeding
1 s, lifetime duration not exceeding 10 hr;
guaranteed by design characterization
ESD Rating, Human Body Model
AEC-Q100-002, all pins
2000
V
ESD Rating, Charged Device Model
AEC-Q100-011, all pins
1050
V
*With respect to GND.
THERMAL CHARACTERISTICS may require derating at maximum conditions
Characteristic
Package Thermal Resistance
Symbol
RθJA
Test Conditions*
4-layer PCB based on JEDEC standard
2-layer PCB with 3.8
RθJP
in.2
of copper area each side
Value
Units
28
ºC/W
32
ºC/W
2
ºC/W
*Additional thermal information available on Allegro website.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A3941
Automotive Full Bridge MOSFET Driver
Functional Block Diagram
Battery +
CP
VBB
V5
CP2
CP1
VBAT
Charge
Pump
Regulator
+5V Reg
VREG
CREG
FF1
FF2
VDSTH
VDRAIN
Diagnostics
and Protection
Charge
Pump
Bootstrap
Monitor
CA
CBOOTA
GHA
High
Side
RGHA
RGHB
RGLA
RGLB
SA
Low
Side
PWMH
GLA
PWML
LSS
Control
Logic
Charge
Pump
Bootstrap
Monitor
PHASE
CB
CBOOTB
GHB
High
Side
SR
SB
RESET
Low
Side
GLB
LSS
RDEAD
GND
PAD
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A3941
Automotive Full Bridge MOSFET Driver
ELECTRICAL CHARACTERISTICS valid at TJ = –40°C to 150°C, VBB = 7 to 50 V, unless noted otherwise
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Units
5.5
–
50
V
Supply and Reference
Load Supply Voltage Functional
Operating Range1
Load Supply Quiescent Current
VREG Output Voltage
VBB
IBBQ
RESET = high, outputs = low, VBB = 12 V
–
10
14
mA
IBBS
RESET = low, Sleep mode, VBB = 12 V
–
–
10
μA
VBB > 9 V, IREG = 0 to 10 mA
12.5
13
13.75
V
7.5 V < VBB ≤ 9 V, IREG = 0 to 7 mA
12.5
13
13.75
V
6 V < VBB ≤ 7.5 V, IREG = 0 to 7 mA
2×VBB
– 2.5
–
–
V
5.5 V < VBB ≤ 6 V, IREG < 5.5 mA
8.5
9.5
–
V
4.5
5
5.5
V
–
15
40
mV
VREG
V5 Output Voltage
V5(out)
No load
V5 Line Regulation
V5(line)
I5 = –2 mA
V5 Load Regulation
V5(load)
I5 = 0 to –2 mA
–
50
100
mV
VBB = 40 V, V5 = 0 V
–
28
35
mA
V5 Short-Circuit Current
Bootstrap Diode Forward Voltage
Bootstrap Diode Resistance
I5M
VfBOOT
rD
ID = 10 mA
0.4
0.7
1.0
V
ID = 100 mA
1.5
2.2
2.8
V
6
10
20
Ω
250
500
750
mA
rD(100mA) =
(VfBOOT(150mA) – VfBOOT(50mA)) / 100 mA
Bootstrap Diode Current Limit
IDBOOT
Top-off Charge Pump Current Limit
ITOCPM
–
400
–
μA
RGSH
250
–
–
kΩ
–
35
–
ns
High-Side Gate Drive Static Load Resistance
Gate Output Drive
Turn-On Time
tr
CLOAD = 1 nF, 20% to 80%
Turn-Off Time
tf
CLOAD = 1 nF, 80% to 20%
–
20
–
ns
TJ = 25°C, IGHx = –150 mA
6
8
12
Ω
TJ = 150°C, IGHx = –150 mA
10
13
16
Ω
TJ = 25°C, IGLx = 150 mA
2
3
4
Ω
Pullup On Resistance
Pulldown On Resistance
RDS(on)UP
RDS(on)DN
TJ = 150°C, IGLx = 150 mA
4.5
6
Ω
–
–
V
VREG
– 0.2
–
–
V
GHx Output Voltage
VGHX
GLx Output Voltage
VGLX
Turn-Off Propagation Delay2
tP(off)
Input change to unloaded gate output
change
60
90
150
ns
Turn-On Propagation Delay2
tP(on)
Input change to unloaded gate output
change
60
90
150
ns
Propagation Delay Matching, Phase-to-Phase
∆tPP
Measured between corresponding
transition points on both phases
–
10
–
ns
Propagation Delay Matching, On-to-Off
∆tOO
Measured across one phase
–
10
–
ns
Dead Time2
tDEAD
Bootstrap capacitor fully charged
3
VCx
– 0.2
RDEAD = 3 kΩ
–
180
–
ns
RDEAD = 30 kΩ
815
960
1110
ns
RDEAD = 240 kΩ
–
3.5
–
μs
RDEAD tied to V5
–
6
–
μs
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A3941
Automotive Full Bridge MOSFET Driver
ELECTRICAL CHARACTERISTICS (continued) valid at TJ = –40°C to 150°C, VBB = 7 to 50 V, unless noted otherwise
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Logic Inputs and Outputs
FF1 and FF2 Fault Output (Open Drain)
VFF(L)
IFF = 1 mA, fault not present
–
–
0.4
V
FF1 and FF2 Fault Output Leakage Current3
IFF(H)
VFF = 5 V, fault present
–1
–
1
μA
RDEAD Current3
IDEAD
RDEAD = GND
–200
–
–70
μA
Input Low Voltage
VIN(L)
–
–
1
V
Input High Voltage
VIN(H)
3.5
–
–
V
Input Hysteresis (Except RESET Pin)
VINhys
300
500
–
mV
200
–
–
mV
–1
–
1
μA
Input Hysteresis (RESET Pin)
Input Current (Except RESET Pin)3
VINRSThys
IIN
0 V < VIN < V5
Input Pulldown Resistor (RESET Pin)
RPD
–
50
–
kΩ
RESET Pulse Time
tRES
0.1
–
3.5
μs
V
Protection
VREG Undervoltage Lockout Threshold
VREGUVon
VREG rising
7.5
8
8.5
6.75
7.25
7.75
V
59
–
69
%VREG
–
13
–
%VREG
VREGUVoff
VREG falling
Bootstrap Undervoltage Threshold
VBOOTUV
Cx with respect to Sx
Bootstrap Undervoltage Hysteresis
VBOOTUVhys
V5 Undervoltage Turn-Off Threshold
V5UVoff
V5 Undervoltage Hysteresis
V5UVhys
VDSTH Input Range
VDSTH
VDSTH Input Current
IDSTH
V5 falling
0 V < VDSTH < 2 V
3.4
3.6
3.8
V
300
400
500
mV
0.1
–
2
V
–
10
30
μA
VDSTH Disable Voltage
VDSDIS
When not connected directly to V5
4.95
–
–
V
VDRAIN Input Voltage
VDRAIN
VDSTH = 2 V, VBB = 12 V,
7
VBB
50
V
VDRAIN Input Current
IDRAIN
VDSTH = 2 V, VBB = 12 V,
0 V < VDRAIN < VBB
–
–
250
μA
Short-to-Ground Threshold Offset4
VSTGO
High-side on, VDSTH ≥ 1 V
–
±100
–
mV
High-side on, VDSTH < 1 V
–150
±50
150
mV
Short-to-Battery Threshold Offset5
VSTBO
Low-side on, VDSTH ≥ 1 V
–
±100
–
mV
Overtemperature Fault Flag Threshold
Overtemperature Fault Hysteresis
Low-side on, VDSTH < 1 V
–150
±50
150
mV
TJF
Temperature increasing
150
170
–
ºC
TJFhys
Recovery = TJF – TJFhys
–
15
–
ºC
1Functions
correctly, but parameters are not guaranteed, below the general limits (7 V).
2See Gate Drive Timing diagrams.
3For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
4As V
Sx decreases, fault occurs if VBAT –VSx > VSTG. STG threshold, VSTG = VDSTH + VSTGO .
5As V
Sx increases, fault occurs if VSx – VLSS > VSTB . STB threshold, VSTB = VDSTH+VSTBO .
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
A3941
Automotive Full Bridge MOSFET Driver
Timing Diagrams
Gate Drive Timing – PWM inputs, Slow Decay, Synchronous Rectification
PWML
PWMH
tP(off)
tP(off)
tP(off)
tP(off)
GHx
GHx
tDEAD
GLx
tDEAD
tDEAD
GLx
SR=1, PWML=1
tDEAD
SR=1, PWMH=1
Gate Drive Timing – PWM inputs, Slow Decay, Diode Rectification
PWML
PWMH
tP(off)
tP(on)
tP(off)
GHx
GHx
GLx
GLx
SR=0, PWML=1
tP(on)
SR=0, PWMH=1
Gate Drive Timing – Phase Input, Fast Decay,
Synchronous Rectification
Gate Drive Timing – PWM Input, Fast Decay,
Diode Rectification
PHASE
PWMH
PWML
tP(off)
tP(off)
tDEAD
tDEAD
tP(off)
GHA
GHA
GLA
GLA
GHB
GHB
GLB
GLB
PWML=1, PWMH=1
tP(on)
PHASE=1
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
A3941
Automotive Full Bridge MOSFET Driver
Functional Description
The A3941 is a full-bridge MOSFET driver (pre-driver) requiring
a single unregulated supply of 7 to 50 V. It includes an integrated
5 V logic supply regulator.
The four high current gate drives are capable of driving a wide
range of N-channel power MOSFETs, and are configured as two
high-side drives and two low-side drives. The A3941 provides
all the necessary circuits to ensure that the gate-source voltage
of both high-side and low-side external FETs are above 10 V, at
supply voltages down to 7 V. For extreme battery voltage drop
conditions, correct functional operation is guaranteed at supply
voltages down to 5.5 V, but with a reduced gate drive voltage.
The A3941 can be driven with a single PWM input from a
microcontroller and can be configured for fast or slow decay.
Fast decay can provide four-quadrant motor control, while slow
decay is suitable for two-quadrant motor control or simple inductive loads. In slow decay, current recirculation can be through
the high-side or the low-side MOSFETs. In either case, bridge
efficiency can be enhanced by synchronous rectification. Crossconduction (shoot through) in the external bridge is avoided by
an adjustable dead time.
A low power sleep mode allows the A3941, the power bridge, and
the load to remain connected to a vehicle battery supply without
the need for an additional supply switch.
The A3941 includes a number of protection features against
undervoltage, overtemperature, and power bridge faults. Fault
states enable responses by the device or by the external controller, depending on the fault condition and logic settings. Two fault
flag outputs, FF1 and FF2, are provided to signal detected faults
to an external controller.
Power Supplies
A single power supply connection is required to the VBB pin
through a reverse voltage protection circuit. The supply should be
decoupled with a ceramic capacitor connected close to the VBB
and ground pins.
The A3941 operates within specified parameters with a VBB
supply from 7 to 50 V and functions correctly with a supply down
to 5.5 V. This provides a very rugged solution for use in the harsh
automotive environment.
V5 Pin A 5 V low current supply for external pullup resistors is
provided by an integrated 5 V regulator. This regulator is also
used by the internal logic circuits and must always be decoupled
by at least a 100 nF capacitor between the V5 pin and GND. The
5 V regulator is disabled when RESET is held low.
Gate Drives
The A3941 is designed to drive external, low on-resistance,
power N-channel MOSFETs. It supplies the large transient currents necessary to quickly charge and discharge the external FET
gate capacitance in order to reduce dissipation in the external
FET during switching. The charge and discharge rate can be
controlled using an external resistor in series with the connection
to the gate of the FET.
Gate Drive Voltage Regulation The gate drives are powered by
an internal regulator which limits the supply to the drives and
therefore the maximum gate voltage. When the VBB supply is
greater than about 16 V, the regulator is a simple linear regulator.
Below 16 V, the regulated supply is maintained by a charge pump
boost converter, which requires a pump capacitor connected
between the CP1 and CP2 pins. This capacitor must have a minimum value of 220 nF, and is typically 470 nF.
The regulated voltage, nominally 13 V, is available on the VREG
pin. A sufficiently large storage capacitor must be connected to
this pin to provide the transient charging current to the low-side
drives and the bootstrap capacitors.
Top-off Charge Pump An additional top-off charge pump is
provided for each phase. The charge pumps allow the high-side
drives to maintain the gate voltage on the external FETs indefinitely, ensuring so-called 100% PWM if required. This is a low
current trickle charge pump, and is operated only after a high-side
FET has been signaled to turn on. The floating high-side gate
drive requires a small bias current (<20 μA) to maintain the highlevel output. Without the top-off charge pump, this bias current
would be drawn from the bootstrap capacitor through the Cx pin.
The charge pump provides sufficient current to ensure that the
bootstrap voltage and thereby the gate-source voltage is maintained at the necessary level.
Note that the charge required for initial turn-on of the high-side
gate is always supplied by the bootstrap capacitor. If the bootstrap
capacitor becomes discharged, the top-off charge pump will not
provide sufficient current to allow the FET to turn on.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
A3941
Automotive Full Bridge MOSFET Driver
In some applications a safety resistor is added between the gate
and source of each FET in the bridge. When a high-side FET is
held in the on-state, the current through the associated high-side
gate-source resistor (RGSH) is provided by the high-side drive and
therefore appears as a static resistive load on the top-off charge
pump. The minimum value of RGSH for which the top-off charge
pump can provide current is shown in the Electrical Characteristics table.
GLA and GLB Pins These are the low-side gate drive outputs for
the external N-channel MOSFETs. External resistors between the
gate drive output and the gate connection to the FET (as close as
possible to the FET) can be used to control the slew rate seen at
the gate, thereby providing some control of the di/dt and dv/dt of
the SA and SB outputs. GLx going high turns on the upper half of
the drive, sourcing current to the gate of the low-side FET in the
external power bridge, turning it on. GLx going low turns on the
lower half of the drive, sinking current from the external FET gate
circuit to the LSS pin, turning off the FET.
LSS Pin This is the low-side return path for discharge of the
capacitance on the FET gates. It should be tied directly to the
common sources of the low-side external FETs through an independent low impedance connection.
RDEAD Pin This pin controls internal generation of dead time
during FET switching.
• When a resistor greater than 3 kΩ is connected between
RDEAD and AGND, cross-conduction is prevented by the gate
drive circuits, which introduce a dead time, tDEAD , between
switching one FET off and the complementary FET on. The
dead time is derived from the resistor value connected between
the RDEAD and AGND pins.
• When RDEAD is connected directly to V5, cross-conduction is
prevented by the gate drive circuits. In this case, tDEAD defaults
to a value of 6 μs typical.
Logic Control Inputs
SA and SB Pins Directly connected to the motor, these terminals
sense the voltages switched across the load. These terminals are
also connected to the negative side of the bootstrap capacitors
and are the negative supply connections for the floating high-side
drives. The discharge current from the high-side FET gate capacitance flows through these connections, which should have low
impedance circuit connections to the FET bridge.
Four low-voltage level digital inputs provide control for the
gate drives. These logic inputs all have a nominal hysteresis of
500 mV to improve noise performance. They are used together
to provide fast decay or slow decay with high-side or low-side
recirculation. They also provide brake, coast, and sleep modes as
defined in tables 1 and 2.
GHA and GHB Pins These terminals are the high-side gate
current in the power bridge. PWMH provides high-side chopping
and PWML provides low-side chopping. When used together
they control the power bridge in fast decay mode. The PWM
options are provided in table 2.
drive outputs for the external N-channel FETs. External resistors
between the gate drive output and the gate connection to the FET
(as close as possible to the FET) can be used to control the slew
rate seen at the gate, thereby controlling the di/dt and dv/dt of the
SA and SB outputs. GHx going high turns on the upper half of
the drive, sourcing current to the gate of the high-side FET in the
external motor-driving bridge, turning it on. GHx going low turns
on the lower half of the drive, sinking current from the external
FET gate circuit to the corresponding Sx pin, turning off the FET.
CA and CB Pins These are the high-side connections for the
bootstrap capacitors and are the positive supply for the high-side
gate drives. The bootstrap capacitors are charged to approximately VREG when the associated output Sx terminal is low.
When the Sx output swings high, the charge on the bootstrap
capacitor causes the voltage at the corresponding Cx terminal to
rise with the output to provide the boosted gate voltage needed
for the high-side FETs.
PWMH and PWML Pins These inputs can be used to control
• Setting PWMH low turns off active high-side drives. This
provides high-side–chopped slow-decay PWM.
• Setting PWML low turns off active low-side drives. This
provides low-side–chopped slow-decay PWM.
• PWMH and PWML may also be connected together and driven
with a single PWM signal. This provides fast-decay PWM.
PHASE Pin The state of the PHASE pin determines the positive
direction of load current (see table 1). The PHASE pin can also
be used as a PWM input when full four-quadrant control (fast
decay synchronous rectification) is required (see table 2).
SR Pin This enables or disables synchronous rectification. When
SR is high, synchronous rectification is enabled. When a PWMoff phase occurs (low on either or both of the PWMH and PWML
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A3941
Automotive Full Bridge MOSFET Driver
Table 1. Phase Control Truth Table
Inputs
Outputs
PWMH
PWML
PHASE
SR
1
1
1
X
1
1
0
X
0
1
X
1
1
0
X
1
0
1
1
0
0
1
0
1
0
1
1
0
0
0
Bridge
GHA GLA GHB GLB
H
SA
SB
H
HS
LS
Mode of Operation
L
L
Bridge driven with A high and B low
L
H
H
L
LS
HS
Bridge driven with B high and A low
L
H
L
H
LS
LS
Slow decay, both low-side on or low-side brake
H
L
H
L
HS
HS
Slow decay, both high-side on or high-side brake
L
L
L
H
Z
LS
Slow decay, current flow A to B, low-side diode rectification
0
L
H
L
L
LS
Z
Slow decay, current flow B to A, low-side diode rectification
0
H
L
L
L
HS
Z
Slow decay, current flow A to B, high-side diode rectification
0
0
L
L
H
L
Z
HS
Slow decay, current flow B to A, high-side diode rectification
X
X
L
L
L
L
Z
Z
Fast decay, diode rectification/coast
X = don’t care (same for input 1 or input 0), HS = high-side FET active, LS = low-side FET active, Z = high impedance, both FETs off
Table 2. PWM Options
Inputsa
PWM Effectb
Decay
Mode of Operation
B to A
Fast
Full four-quadrant control, zero average load current at 50% PWM
Coast
Fast
Fast decay, diode recirculation or coast
Brake
Slow
High-side PWM, low-side MOSFET recirculation
Brake
Slow
Low-side PWM, high-side MOSFET recirculation
Brakec
Slow
High-side PWM, low-side diode recirculation
Brakec
Slow
Low-side PWM, high-side diode recirculation
Coast
Fast
Coast, all MOSFETs off
SR
PWMH
PWML
PHASE
100%
0%
X
1
1
PWM
A to B
0
PWM
PWM
1
A to B
0
B to A
1
PWM
1
1
A to B
0
B to A
1
1
PWM
1
A to B
0
B to A
0
PWM
1
1
A to B
0
B to A
0
1
PWM
1
A to B
0
B to A
X
0
0
X
Coast
aX
indicates don’t care condition. The action is the same for input 1 or input 0.
Effect indicates the effect on the load current direction or the equivalent action.
cWith SR disabled, braking is only effective in one direction when sufficient forward voltage is available to allow the diode to conduct.
bPWM
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
A3941
Automotive Full Bridge MOSFET Driver
pins), synchronous rectification turns on the MOSFET that is
complementary to the one that is turned off. This ensures that the
current passes through the lower resistance MOSFET rather than
the diode.
When SR is low, synchronous rectification is disabled. In this
case, fewer MOSFET switching cycles occur, reducing dissipation in the A3941. However, load current recirculates through the
higher resistance body diode of the power MOSFETs, causing
greater power dissipation in the power bridge.
RESET Pin This is an active-low input, and when active it allows
the A3941 to enter sleep mode. When RESET is held low, the
regulator and all internal circuitry are disabled and the A3941
enters sleep mode. Before fully entering sleep mode, there is a
short delay while the regulator decoupling and storage capacitors
discharge. This typically takes a few milliseconds, depending on
the application conditions and component values.
During sleep mode, current consumption from the VBB supply
is reduced to a minimal level. In addition, latched faults and the
corresponding fault flags are cleared. When the A3941 is coming
out of sleep mode, the protection logic ensures that the gate drive
outputs are off until the charge pump reaches its correct operating condition. The charge pump stabilizes in approximately 3 ms
under nominal conditions.
RESET can be used also to clear latched fault flags without
entering sleep mode. To do so, hold RESET low for less then the
reset pulse time, tRES. This clears any latched fault that disables
the outputs, such as short circuit detection or bootstrap capacitor
undervoltage.
Note that the A3941 can be configured to start without any external logic input. To do so, pull up the RESET pin to VBB by means
of an external resistor. The resistor value should be between
20 and 33 kΩ.
Coast and Brake States
To put the power bridge into a coast state, that is all power bridge
MOSFETs switched off, the two PWM inputs, PWMH and
PWML, must be held low and at the same time SR must be held
low. This forces all gate drive outputs low.
Braking is achieved by forcing the power bridge to apply a short
across the load, allowing the back EMF of the load to generate a
braking torque.
Several brake states are possible using combinations of inputs
on PWMH, PWML, and SR. For example, holding PWML and
SR high, while PWMH is low, turns on both low-side FETs to
short the load. The shorting path is always present and provides
braking in both directions of motor rotation. Another example is
holding SR low, when PWML is high and PWMH is low, making only one low-side FET active, and the braking current flow
through the body diode of the opposite low-side FET. This provides braking in only one direction, because the diode does not
permit the braking current to flow if the motor is reversed. Also,
the braking current can be made to circulate around the high-side
switches by swapping PWMH and PWML.
Diagnostics
Several diagnostic features are integrated into the A3941 to
provide indication of fault conditions and, if required, take action
to prevent permanent damage. In addition to system-wide faults
such as undervoltage and overtemperature, the A3941 integrates
individual drain-source monitors for each external FET, to provide short circuit detection.
Diagnostic Management Pins
VDSTH Pin Faults on the external FETs are determined by
measuring the drain-source voltage, VDS , of each active FET
and comparing it to the threshold voltage applied to the VDSTH
input, VDSTH. To avoid false fault detection during switching
transients, the comparison is delayed by an internal blanking
timer. If the voltage applied to the VDSTH pin is greater than the
disable threshold voltage, VDSDIS , then FET short circuit detection is disabled.
VDRAIN Pin This is a low current sense input from the top of the
external FET bridge. This input allows accurate measurement of
the voltage at the drain of the high-side FETs. It should be connected directly to the common connection point for the drains of
the power bridge FETs at the positive supply connection point.
The input current to the VDRAIN pin is proportional to the voltage on the VDSTH pin and can be approximated by:
IVDRAIN = 72 × VDSTH + 52 ,
where IVDRAIN is the current into the VDRAIN pin, in μA, and
VDSTH is the voltage on the VDSTH pin, in V.
FF1 and FF2 Pins These are open drain output fault flags, which
indicate fault conditions by their state, as shown in table 3. In
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
A3941
Automotive Full Bridge MOSFET Driver
the event that two or more faults are detected simultaneously, the
state of the fault flags will be determined by a logical OR of the
flag states for all detected faults.
Table 3. Fault Definitions
Flag State
FF1
FF2
Fault Description
Disable
Outputs*
Fault
Latched
Low
Low
No fault
No
–
Low
High
Short-to-ground
Yes
Yes
Low
High
Short-to-supply
Yes
Yes
Low
High
Shorted load
Yes
Yes
High
Low
Overtemperature
No
No
High
High
V5 undervoltage
Yes
No
High
High
VREG undervoltage
Yes
No
High
High
Bootstrap undervoltage
Yes
Yes
*Yes indicates all gate drives low, and all FETs off.
Bootstrap Capacitor Undervoltage The A3941 monitors the
voltage across the individual bootstrap capacitors to ensure they
have sufficient charge to supply the current pulse for the highside drive. Before a high-side drive can be turned on, the voltage
across the associated bootstrap capacitor must be higher than the
turn-on voltage limit. If this is not the case, then the A3941 will
start a bootstrap charge cycle by activating the complementary
low-side drive. Under normal circumstances, this will charge the
bootstrap capacitor above the turn-on voltage in a few microseconds and the high-side drive will then be enabled.
The bootstrap voltage monitor remains active while the high-side
drive is active and, if the voltage drops below the turn-off voltage, a charge cycle is initiated.
In either case, if there is a fault that prevents the bootstrap capacitor charging, then the charge cycle will timeout, the fault flags
(indicating an undervoltage) will be set, and the outputs will be
disabled. The bootstrap undervoltage fault state remains latched
until RESET is set low.
Fault States
V5 Undervoltage The output of the logic supply regulator volt-
Overtemperature If the junction temperature exceeds the over-
age at V5 is monitored to ensure correct logical operation. If
the voltage at V5, V5 , drops below the falling V5 undervoltage
lockout threshold, V5UVoff , then the A3941 will enter the V5
undervoltage fault state. In this fault state, both FF1 and FF2 will
be high, and the outputs will be disabled. In addition, because
the state of other reported faults cannot be guaranteed, all fault
states and fault flags are reset and replaced by the fault flags corresponding to a V5 undervoltage fault state. For example, a V5
undervoltage will reset an existing short circuit fault condition
and replace it with a V5 undervoltage fault. The V5 undervoltage
fault state and the fault flags will be cleared when V5 rises above
the rising V5 undervoltage lockout threshold defined by V5UVoff
+ V5UVhys.
temperature threshold, typically 165°C, the A3941 will enter the
overtemperature fault state and FF1 will go high. The overtemperature fault state, and FF1, will only be cleared when the temperature drops below the recovery level defined by TJF – TJFhys .
No circuitry will be disabled. External control circuits must take
action to limit the power dissipation in some way so as to prevent
overtemperature damage to the A3941 chip and unpredictable
device operation.
VREG Undervoltage VREG supplies the low-side gate driver
and the bootstrap charge current. It is critical to ensure that the
voltages are sufficiently high before enabling any of the outputs.
If the voltage at VREG, VREG , drops below the falling VREG
undervoltage lockout threshold, VREGUVoff , then the A3941 will
enter the VREG undervoltage fault state. In this fault state, both
FF1 and FF2 will be high, and the outputs will be disabled. The
VREG undervoltage fault state and the fault flags will be cleared
when VREG rises above the rising VREG undervoltage lockout
threshold, VREGUVon.
The VREG undervoltage monitor circuit is active during power-up, and the A3941 remains in the VREG undervoltage fault
state until VREG is greater than the rising VREG undervoltage
lockout threshold, VREGUVon.
The V5 undervoltage monitor circuit is active during power-up,
and the A3941 remains in the V5 undervoltage fault state until V5
is greater than the rising VREG undervoltage lockout threshold,
V5UVoff +V5UVhys.
Short Fault Operation Shorts in the power bridge are determined
by monitoring the drain-souce voltage, VDS , of each active FET
and comparing it to the fault threshold voltage at the VDSTH pin.
Because power MOSFETs take a finite time to reach the rated
on-resistance, the measured drain-source voltages will show a
fault as the phase switches. To avoid such false short fault detec-
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
A3941
Automotive Full Bridge MOSFET Driver
tions, the output from the comparators are ignored under two
conditions:
▪ while the external FET is off, and
▪ until the end of the period, referred to as the fault blank time,
after the FET is turned on.
When the FET is turned on, if the drain-source voltage exceeds
the voltage at the VDSTH pin at any time after the fault blank
time, then a short fault will be detected. This fault will be latched
and the FET disabled until reset.
In applications where short detection is not required, this feature
may be disabled by connecting VDSTH to V5 or by applying a
voltage greater than the disable threshold voltage, VDSDIS . This
completely disables the VDS monitor circuits, preventing detection of short faults and any indication of short faults by the fault
flags. In this condition the external FETs will not be protected by
the A3941.
Short to Supply When VDSTH is less than the disable threshold
voltage, VDSDIS, a short from any of the motor phase connections to the battery or VBB connection is detected by monitoring
the voltage across the low-side FETs in each phase, using the
appropriate Sx pin and the LSS pin. This drain-source voltage,
VDS, is continuously compared to the voltage on the VDSTH pin.
The result of this comparison is ignored if the FET is not active.
It also is ignored for one fault blank time interval after the FET is
turned on. If, when the comparator is not being ignored, its output
indicates that VDS exceeds the voltage at the VDSTH pin, then
FF2 will be high.
Short to Ground When VDSTH is less than the disable threshold voltage, VDSDIS , a short from any of the motor phase connections to ground is detected by monitoring the voltage across
the high-side FETs in each phase, using the appropriate Sx pin
and the voltage at VDRAIN. This drain-source voltage, VDS , is
continuously compared to the voltage on the VDSTH pin. The
result of this comparison is ignored if the FET is not active. It
also is ignored for one fault blank time interval after the FET is
turned on. If, when the comparator is not being ignored, its output
indicates that VDS exceeds the voltage at the VDSTH pin, FF2
will be high.
Shorted Load The short-to-ground and short-to-supply monitor
circuits will also detect a short across a motor phase winding. In
most cases, a shorted winding will be indicated by a high-side
and low-side fault being detected at the same time. In some cases
the relative impedances may permit only one of the shorts to be
detected.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
A3941
Automotive Full Bridge MOSFET Driver
Applications Information
Power Bridge Management Using PWM Control
The A3941 provides two PWM control signals, a phase control
for current direction, and the ability to enable or disable synchronous rectification. This allows a wide variety of full bridge
control schemes to be implemented. The six basic schemes are
shown in table 2 and described further below.
Slow Decay Slow decay is the simplest and most common
control configuration. Figure 1A shows the path of the bridge
and load current when a PWM signal is applied to PWMH, with
PWML and PHASE tied high, and SR low.
In this case the high-side MOSFETs are switched off during the
current decay time (PWM off-time) and load current recirculates
through the low-side MOSFETs. This is commonly referred to as
high-side chopping or high-side PWM. The recirculating current
flows through the body diode of the low-side MOSFET, which
is complementary to the high-side MOSFET being switched off.
Improved efficiency can be achieved by turning on the complementary MOSFETs during the PWM off-time to short the reverse
diode and provide synchronous rectification. This can be easily
achieved by taking SR high as shown in figure 1B.
By applying the PWM signal to the PWML pin instead of the
PWMH pin, the low-side MOSFET is turned off during the PWM
off-time and the load current recirculates through the high-side
MOSFETs as in figure 1C.
GHA
Fast decay with diode recirculation is achieved by applying a
PWM signal at the same time to both PWM inputs, PWMH and
PWML, with SR disabled (figure 2A). Because current recirculation is through the body diodes of the MOSFETs, the average load current cannot be negative so, as for the slow decay
GHA
GLB
GLA
GHB
LOAD
GLA
Inputs
PWMH
PWML
PHASE
SR
LOAD
GLB
Driving
Outputs
1 Phase A B
Recirculating
Inputs
Outputs
0 Phase A B
PWMH
1
1
0
PWML
PHASE
SR
GHx
H
L
GLx
L
H
1
1
0
GHx
H
L
GLx
L
H
(A) Slow decay, diode recirculation, high-side PWM
GHA
GHB
GHA
GHB
LOAD
GLA
Inputs
PWMH
PWML
PHASE
SR
LOAD
GLB
GLA
GLB
Driving
Outputs
1 Phase A B
Recirculating
Inputs
Outputs
0 Phase A B
PWMH
1
1
1
PWML
PHASE
SR
In the three slow decay configurations shown, the direction of the
average current in the load can be reversed by simply applying a
low level to the PHASE pin. Referring to the slow decay entries
in table 2, when PHASE is high the average current flows from
the phase A connection (SA) to the phase B connection (SB).
When PHASE is low the direction is from B to A.
Fast Decay While slow decay usually provides sufficient control
over the load current for most simple control systems, it is possible that current control stability can be affected by, for example,
the back EMF of the load. In these cases, typically actuator positioning or servo control systems, it may be necessary to use fast
decay to provide continuous control over the load current. The
A3941 can be configured to provide fast decay using either diode
recirculation or synchronous rectification.
GHB
GHx
H
L
GLx
L
H
1
1
1
GHx
L
L
GLx
H
H
(B) Slow decay, SR active, high-side PWM
GHA
GHB
GHA
GHB
LOAD
GLA
Inputs
PWMH
PWML
PHASE
SR
LOAD
GLB
GLA
GLB
Driving
Outputs
1 Phase A B
Recirculating
Inputs
Outputs
1 Phase A B
PWMH
1
1
1
PWML
PHASE
SR
GHx
H
L
GLx
L
H
0
1
1
GHx
H
H
GLx
L
L
(C) Slow decay, SR active, low-side PWM
Figure 1. Slow decay power bridge current paths
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
A3941
Automotive Full Bridge MOSFET Driver
schemes, the PHASE input is still required to reverse the load
current.
GHA
Although fast decay with diode rectification provides a higher
degree of current control than slow decay schemes, it still may
not provide sufficient control for servo systems where full fourquadrant control is required. This is only possible using fast
decay with synchronous rectification. By applying the PWM signal to the PHASE input, and holding PWMH and PWML and SR
high (figure 2B), the load current can be controlled in both directions with a single PWM signal. Because all four MOSFETs in
the bridge change state, the supply can be directly applied to the
load in either direction. The effect is: when the PWM duty cycle
is less than 50%, the average current flows from B to A; when
greater than 50%, the average current flows from A to B; and
when at 50%, the average current is zero. This allows the load
current to be independent of any back EMF voltage generated, for
example by a rotating motor, and effectively allowing the applied
torque to work with or against a motor in either direction.
GHA
GLB
GLA
GHB
LOAD
GLA
Inputs
PWMH
PWML
PHASE
SR
LOAD
GLB
Driving
Outputs
1 Phase A B
Recirculating
Inputs
Outputs
0 Phase A B
PWMH
1
1
0
PWML
PHASE
SR
GHx
H
L
GLx
L
H
0
1
0
GHx
L
L
GLx
L
L
(A) Fast decay, diode recirculation
GHA
GHB
GHA
GLB
GLA
GHB
LOAD
GLA
Inputs
Synchronous Rectification Synchronous rectification is used to
reduce power dissipation in the external MOSFETs. As described
above, the A3941 can be instructed to turn on the appropriate
low-side and high-side driver during the load current recirculation
PWM off-cycle. During the decay time, synchronous rectification allows current to flow through the selected MOSFET, rather
than through the source-drain body diode. The body diodes of the
recirculating power MOSFETs will conduct only during the dead
time that occurs at each PWM transition.
GHB
PWMH
PWML
PHASE
SR
LOAD
GLB
Driving
Outputs
1 Phase A B
Recirculating
Inputs
Outputs
1 Phase A B
PWMH
1
1
1
PWML
PHASE
SR
GHx
H
L
GLx
L
H
1
0
1
GHx
L
H
GLx
H
L
(B) Fast decay, SR active, full four-quadrant control
Figure 2. Fast decay power bridge current paths
4.5
4.0
3.5
3.0
To prevent cross-conduction (shoot through) in any phase of
the power FET bridge, it is necessary to have a dead time delay,
tDEAD , between a high-side or low-side turn-off and the next
complementary turn-on event. The potential for cross-conduction occurs when any complementary high-side and low-side pair
of FETs are switched at the same time; for example, when using
synchronous rectification or after a bootstrap capacitor charging cycle. In the A3941, the dead time for both phases is set by
a single dead-time resistor, RDEAD , between the RDEAD and
AGND pins.
t DEAD (μs)
Dead Time
2.5
2.0
1.5
1.0
0.5
0
0
50
100
150
200 250 300
RDEAD (kΩ)
350
400
450
Figure 3. Dead time versus RDEAD , (full range)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
14
A3941
Automotive Full Bridge MOSFET Driver
For RDEAD values between 3 kΩ and 240 kΩ, at 25°C the nominal value of tDEAD in ns can be approximated by:
7200
, (1)
tDEAD(nom) = 50 +
1.2 + (200 / RDEAD)
where RDEAD is in kΩ. Greatest accuracy is obtained for values
of RDEAD between 6 and 60 kΩ, which are shown in figure 3.
The IDEAD current can be estimated by:
1.2
IDEAD =
RDEAD
.
(2)
The maximum dead time, 6 μs typical, can be set by connecting
the RDEAD pin directly to the V5 pin.
The choice of power FET and external series gate resistance
determine the selection of the dead-time resistor, RDEAD. The
dead time should be long enough to ensure that one FET in a
phase has stopped conducting before the complementary FET
starts conducting. This should also take into account the tolerance
and variation of the FET gate capacitance, the series gate resistance, and the on-resistance of the A3941 internal drives.
Dead time will be present only if the on-command for one FET
occurs within tDEAD after the off-command for its complementary
FET. In the case where one side of a phase drive is permanently
off, for example when using diode rectification with slow decay,
then the dead time will not occur. In this case the gate drive will
turn on within the specified propagation delay after the corresponding phase input goes high. (Refer to the Gate Drive Timing
diagrams.)
PWML=0). This effectively short-circuits the back EMF of the
motor, creating a breaking torque.
During braking, the load current can be approximated by:
VBEMF
IBRAKE =
,
RL
(3)
where VBEMF is the voltage generated by the motor and RL is the
resistance of the phase winding.
Care must be taken during braking to ensure that maximum ratings of the power FETs are not exceeded. Dynamic braking is
equivalent to slow decay with synchronous rectification.
Bootstrap Capacitor Selection
The bootstrap capacitors, CBOOTx, must be correctly selected to
ensure proper operation of the A3941. If the capacitances are too
high, time will be wasted charging the capacitor, resulting in a
limit on the maximum duty cycle and the PWM frequency. If the
capacitances are too low, there can be a large voltage drop at the
time the charge is transferred from CBOOTx to the FET gate, due
to charge sharing.
To keep this voltage drop small, the charge in the bootstrap
capacitor, QBOOT, should be much larger than the charge required
by the gate of the FET, QGATE. A factor of 20 is a reasonable
value, and the following formula can be used to calculate the
value for CBOOT :
QBOOT = CBOOT × VBOOT = QGATE × 20 ,
Fault Blank Time
To avoid false short fault detection, the output from the VDS
monitor for any FET is ignored when that FET is off and for a
period of time after it is turned on. This period of time is the fault
blank time. Its length is the dead time, tDEAD , plus an additional
period of time that compensates for the delay in the VDS monitors. This additional delay is typically 300 to 600 ns.
therefore:
CBOOT =
The A3941 can be used to perform dynamic braking either by
forcing all low-side FETs on and all high-side FETs off (SR=1,
PWMH=0, and PWML=1) or conversely by forcing all lowside FETs off and all high-side FETs on (SR=1, PWMH=1, and
VBOOT
,
(4)
where VBOOT is the voltage across the bootstrap capacitor.
The voltage drop across the bootstrap capacitor as the FET is
being turned on, ∆V , can be approximated by:
∆V ≈
Braking
QGATE × 20
QGATE
.
CBOOT
(5)
So, for a factor of 20, ∆V would be approximately 5% of VBOOT .
The maximum voltage across the bootstrap capacitor under
normal operating conditions is VREG(max). However, in some
circumstances the voltage may transiently reach 18 V, the clamp
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
A3941
Automotive Full Bridge MOSFET Driver
voltage of the Zener diodes between the Cx and Sx pins. In most
applications, with a good ceramic capacitor the working voltage
can be limited to 16 V.
Bootstrap Charging
It is good practice to ensure the high-side bootstrap capacitor is
completely charged before a high-side PWM cycle is requested.
The time required to charge the capacitor, tCHARGE (μs), is
approximated by:
tCHARGE =
CBOOT × ∆V
100
,
(6)
where CBOOT is the value of the bootstrap capacitor, in nF, and
∆V is the required voltage of the bootstrap capacitor.
At power-up and when the drives have been disabled for a long
time, the bootstrap capacitor can be completely discharged. In
this case ∆V can be considered to be the full high-side drive
voltage, 12 V. Otherwise, ∆V is the amount of voltage dropped
during the charge transfer, which should be 400 mV or less.
The capacitor is charged whenever the Sx pin is pulled low and
current flows from VREG through the internal bootstrap diode
circuit to CBOOT.
Bootstrap Charge Management
The A3941 provides automatic bootstrap capacitor charge
management. The bootstrap capacitor voltage for each phase
is continuously checked to ensure that it is above the bootstrap
under-voltage threshold, VBOOTUV. If the bootstrap capacitor voltage drops below this threshold, the A3941 will turn on the necessary low-side FET, and continue charging until the bootstrap
capacitor exceeds the undervoltage threshold plus the hysteresis,
VBOOTUV + VBOOTUVhys. The minimum charge time is typically
7 μs, but may be longer for very large values of bootstrap capacitor (>1000 nF). If the bootstrap capacitor voltage does not reach
the threshold within approximately 200 μs, an undervoltage fault
will be flagged.
capacitors. When a low-side FET is turned on, the gate-drive
circuit will provide the high transient current to the gate that is
necessary to turn on the FET quickly. This current, which can be
several hundred milliamperes, cannot be provided directly by the
limited output of the VREG regulator, and must be supplied by an
external capacitor connected to VREG.
The turn-on current for the high-side FET is similar in value to
that for the low-side FET, but is mainly supplied by the bootstrap capacitor. However the bootstrap capacitor must then be
recharged from the VREG regulator output. Unfortunately the
bootstrap recharge can occur a very short time after the lowside turn-on occurs. This requires that the value of the capacitor
connected between VREG and AGND should be high enough to
minimize the transient voltage drop on VREG for the combination of a low-side FET turn-on and a bootstrap capacitor recharge.
A value of 20 × CBOOT is a reasonable value. The maximum
working voltage will never exceed VREG , so the capacitor can be
rated as low as 15 V. This capacitor should be placed as close as
possible to the VREG pin.
Supply Decoupling
Because this is a switching circuit, there are current spikes from all
supplies at the switching points. As with all such circuits, the power
supply connections should be decoupled with a ceramic capacitor,
typically 100 nF, between the supply pin and ground. These capacitors should be connected as close as possible to the device supply
pins VBB and V5, and the ground pin, GND.
Power Dissipation
In applications where a high ambient temperature is expected, the
on-chip power dissipation may become a critical factor. Careful
attention should be paid to ensure the operating conditions allow
the A3941 to remain in a safe range of junction temperature.
The power consumed by the A3941, PD, can be estimated by:
PD = PBIAS + PCPUMP + PSWITCHING ,
VREG Capacitor Selection
The internal reference, VREG, supplies current for the low-side
gate drive circuits and the charging current for the bootstrap
(7)
given:
PBIAS = VBB × IBB ;
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
(8)
16
A3941
PCPUMP = [( 2 VBB) – VREG] IAV
or
= [VBB – VREG] IAV
Automotive Full Bridge MOSFET Driver
, for VBB < 15 V,
, for VBB ≥ 15 V,
PSWITCHING = QGATE × VREG × N × fPWM × Ratio ;
(9)
(10)
where:
IAV = QGATE × N × fPWM ,
N is the number of FETs switching during a PWM cycle, and
10
.
Ratio =
RGATE + 10
N = 1 for slow decay with diode recirculation, N = 2 for slow decay
with synchronous rectification or for fast decay with diode recirculation, and N = 4 for fast decay with synchronous rectification.
Layout Recommendations
Careful consideration must be given to PCB layout when designing high frequency, fast switching, high current circuits. The
following are recommendations regarding some of these considerations:
• The A3941 ground, GND, and the high-current return of the
external FETs should return separately to the negative side
of the motor supply filtering capacitor. This will minimize
the effect of switching noise on the device logic and analog
reference.
• The exposed thermal pad should be connected to the GND
pin and may form part of the Controller Supply ground (see
figure 4).
• Minimize stray inductance by using short, wide copper traces at
the drain and source terminals of all power FETs. This includes
motor lead connections, the input power bus, and the common
source of the low-side power FETs. This will minimize voltages
induced by fast switching of large load currents.
• Consider the use of small (100 nF) ceramic decoupling
capacitors across the sources and drains of the power FETs to
limit fast transient voltage spikes caused by the inductance of
the circuit trace.
• Keep the gate discharge return connections Sx and LSS as short
as possible. Any inductance on these traces will cause negative
transitions on the corresponding A3941 pins, which may exceed
the absolute maximum ratings. If this is likely, consider the use
of clamping diodes to limit the negative excursion on these pins
with respect to GND.
• Sensitive connections such as RDEAD and VDSTH, which
have very little ground current, should be connected to the Quiet
ground (refer to figure 4), which is connected independently,
closest to the GND pin. These sensitive components should
never be connected directly to the supply common or to a
common ground plane. They must be referenced directly to the
GND pin.
• The supply decoupling for VBB, VREG, and V5 should
be connected to the Controller Supply ground, which is
independently connected close to the GND pin. The decoupling
capacitors should also be connected as close as practicable to
the relevant supply pin.
• If layout space is limited, then the Quiet and Controller Supply
grounds may be combined. In this case, ensure that the ground
return of the dead time resistor is close to the GND pin.
• Check the peak voltage excursion of the transients on the LSS
pin with reference to the GND pin, using a close grounded (tip
and barrel) probe. If the voltage at LSS exceeds the absolute
maximum shown in this datasheet, add either or both of
additional clamping and capacitance between the LSS pin and
the GND pin, as shown in figure 4.
• Gate charge drive paths and gate discharge return paths may
carry a large transient current pulse. Therefore, the traces from
GHx, GLx, Sx, and LSS should be as short as possible to reduce
the circuit trace inductance.
• Provide an independent connection from LSS to the common
point of the power bridge. It is not recommended to connect
LSS directly to the GND pin, as this may inject noise into
sensitive functions such as the timer for dead time.
• A low-cost diode can be placed in the connection to VBB to
provide reverse battery protection. In reverse battery conditions,
it is possible to use the body diodes of the power FETs to clamp
the reverse voltage to approximately 4 V. In this case, the
additional diode in the VBB connection will prevent damage
to the A3941 and the VDRAIN input will survive the
reverse voltage.
Note that the above are only recommendations. Each application
is different and may encounter different sensitivities. A driver
running a few amps will be less susceptible than one running with
150 A, and each design should be tested at the maximum current
to ensure any parasitic effects are eliminated.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
17
A3941
Automotive Full Bridge MOSFET Driver
Optional reverse
battery protection
VBB VDRAIN
+ Supply
GHB
VREG
GHA
A3941
VS
SA
Motor
SB
GLA
VDSTH
GLB
RDEAD
GND
LSS
RS
Optional components
to limit LSS transients
Quiet Ground
Supply
Common
Power Ground
Controller Supply Ground
Figure 4. Supply routing suggestions
Input and Output Structures
CP1
CP2
VDRAIN
VBB
VS
Cx
VBB
20 V
18 V
19 V
18 V
ESD
18 V
GHx
19 V
18 V
18 V
6V
20 V
Sx
(B) Supply protection structures
VREG
18 V
ESD
18 V
GLx
3 kΩ
10 Ω
FFx
RESET
50 kΩ
LSS
6V
(A) Gate drive outputs
(C) Fault output
(D) RESET input
ESD
ESD
6V
ESD
1.2 V
PWMx
SR
PHASE
VDSTH
8.5 V
(E) Logic inputs, no pulldown
100 Ω
1 kΩ
3 kΩ
RDEAD
8.5 V
(F) VDS monitor threshold input
8.5 V
(G) RDEAD
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
18
A3941
Automotive Full Bridge MOSFET Driver
Pin-out Diagram
1
LSS
2
28
VDSTH
27
GLB
RDEAD
3
26
FF2
SB
4
25
FF1
GHB
5
24
RESET
CB
6
23
PWMH
VREG
7
22
PWML
VREG
8
21
SR
CA
9
20
V5
GHA
10
19
PHASE
SA
11
18
GND
GLA
12
17
GND
VBB
13
16
CP1
VBB
14
15
CP2
tDEAD
Reg
Control Logic
VDRAIN
Reg
Charge
Pump
Terminal List
Number
Name
Description
Number
Name
1
VDRAIN
High-side common drain
16
CP1
Pump capacitor
2
LSS
Low-side common source
17
GND
Ground
3
GLB
Low-side gate drive B
18
GND
Ground
4
SB
Load connection B
19
PHASE
5
GHB
High-side gate drive B
20
V5
5 V regulator
6
CB
Bootstrap capacitor B
21
SR
SR control input
7
VREG
Regulated 13 V
22
PWML
Low-side PWM control input
8
VREG
Regulated 13 V
23
PWMH
High-side PWM control input
9
CA
Bootstrap capacitor A
24
RESET
10
GHA
High-side gate drive A
25
FF1
Description
Phase control input
Reset input
Fault Flag 1 output
11
SA
Load connection A
26
FF2
12
GLA
Low-side gate drive A
27
RDEAD
Dead time setting input
Fault Flag 2 output
13
VBB
Main supply
28
VDSTH
VDS threshold level Input
14
VBB
Main supply
15
CP2
Pump capacitor
–
PAD
Exposed pad for enhanced thermal
dissipation (underside)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
19
A3941
Automotive Full Bridge MOSFET Driver
Package LP 28-Pin TSSOP with Exposed Thermal Pad
0.45
9.70 ±0.10
4° ±4
28
+0.05
0.15 –0.06
0.65
28
1.65
B
3.00
4.40 ±0.10
6.40 ±0.20
3.00
6.10
0.60 ±0.15
A
1
(1.00)
2
5.00
0.25
28X
SEATING
PLANE
0.10 C
+0.05
0.25 –0.06
0.65
C
SEATING PLANE
GAUGE PLANE
1 2
5.00
C
PCB Layout Reference View
1.20 MAX
0.10 MAX
For reference only
(reference JEDEC MO-153 AET)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
A Terminal #1 mark area
B Exposed thermal pad (bottom surface)
C Reference land pattern layout (reference IPC7351 SOP65P640X120-29CM);
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
20
A3941
Automotive Full Bridge MOSFET Driver
Revision History
Revision
Revision Date
Rev. 5
August 23, 2011
Description of Revision
Change in I5M
Copyright ©2008-2013, 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:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
21
Similar pages