A4955
Full-Bridge PWM Gate Driver
FEATURES AND BENEFITS
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DESCRIPTION
Standard IN1/IN2 control logic
Overcurrent indication
Adjustable off-time and blank-time
Adjustable current limit
Adjustable gate drive
Synchronous rectification
Internal UVLO
Crossover-current protection
MOSFET VDS protection
Voltage output proportional to load current
PACKAGES:
20-Pin QFN (suffix “ES”)
with Exposed Thermal Pad
Designed for pulse-width-modulated (PWM) control of DC
motors, the A4955 is capable of 50 V operation and provides
gate drive for an all N-channel external MOSFET bridge.
Input terminals are provided for use in controlling the speed and
direction of a DC motor with externally applied PWM control
signals. Internal synchronous rectification control circuitry is
provided to lower power dissipation during PWM operation.
Internal circuit protection includes VDS protection, thermal
shutdown with hysteresis, undervoltage monitoring of VBB,
and crossover-current protection.
The A4955 is supplied in a low-profile 4 × 4 mm, 20-contact
QFN package (suffix “ES”) and a 20-lead eTSSOP (suffix
“LP”), both with exposed thermal pad.
20-Pin eTSSOP (suffix “LP”)
with Exposed Thermal Pad
Not to scale
CP2
CP1
0.1 µF
TSD
UVLO
VIN
CHARGE PUMP
VCP
ISET
VBB
VREG
0.1 µF
VCP
RC
STANDBY
GHA
GHB
SLEEPn
GHA
SB
Control
Logic
IN1
GATE
DRIVE
IN2
OCLn
System
Controller
OCL
Filter
optional
AIOUT
HOLD
SA
SA
GLA
GLB
GLA
×10
+
SENSE
RSENSE
Inrush current limit =
VREF/10 * RSENSE
–
VREF
÷10
GND
Functional Block Diagram
A4955-DS, Rev. 5
MCO-0000347
July 18, 2022
A4955
Full-Bridge PWM Gate Driver
SPECIFICATIONS
SELECTION GUIDE
Part Number
Ambient Temperature Range
Packing
A4955GESTR-T
–40°C to 105°C
1500 pieces per 7-inch reel
A4955GLPTR-T
–40°C to 105°C
4000 pieces per 13-inch reel
A4955KLPTR-T [1]
–40°C to 125°C
4000 pieces per 13-inch reel
Notes
AEC-Q100 Qualified
[1] The A4955KLPTR-T variant is in production but have been determined to be NOT FOR NEW DESIGN. This classification indicates that sale of this
device is currently restricted to existing customer applications. The device should not be purchased for new design applications because obsolescence in
the near future is probable. Samples are no longer available. Date of status change: July 1, 2019.
ABSOLUTE MAXIMUM RATINGS
Characteristic
Symbol
Load Supply Voltage
VBB
Motor Outputs
VSx
Notes
VSx – VSENSE; VBB – VSx
Rating
Unit
50
V
–2 to 52
V
–0.5 to 0.5
V
SENSE
VSENSE
–4 to 4
V
OCLn
VOCLn
–0.3 to 5.5
V
VREF
VREF
–0.3 to 5.5
V
ISET
VISET
–0.3 to 5.5
V
AIOUT
VAIOUT
–0.3 to 5.5
V
–0.3 to 5.5
V
Logic Input Voltage Range
VIN
tW < 500 ns
SLEEPn, IN1, IN2
Junction Temperature
TJ
150
°C
Storage Temperature Range
TS
–55 to 150
°C
Range G
–40 to 105
°C
Range K
–40 to 125
°C
Operating Temperature Range
TA
THERMAL CHARACTERISTICS (may require derating at maximum conditions; see application information)
Characteristic
ES Package
LP Package
Symbol
RθJA
Test Conditions*
4-Layer PCB, 1
in.2
4-Layer PCB, 1
in.2
Value
Unit
copper
37
°C/W
copper
28
°C/W
*Power dissipation and thermal limits must be observed.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
2
A4955
RC
IN1
IN2
VREF
OCLn
GND
20
19
18
17
16
Full-Bridge PWM Gate Driver
AIOUT
1
20
CP1
2
19
VBB
ISET
1
15
AIOUT
OCLn
3
18
CP2
SLEEPn
2
14
GND
VREF
4
17
VCP
SENSE
3
13
CP1
IN2
5
16
SA
PAD
PAD
8
9
10
GHA
SA
VCP
CP2
7
VBB
11
SB
12
5
6
4
GLA
GHB
GLB
IN1
6
15
GHA
RC
7
14
SB
ISET
8
13
GHB
SLEEPn
9
12
GLA
SENSE
10
11
GLB
Package ES, 20-Pin QFN Pinouts
Package LP, 20-Pin eTSSOP Pinouts
Terminal List Table
Name
Number
ES Package
LP Package
Function
ISET
1
8
Terminal to set gate drive current
SLEEPn
2
9
Sleep input, active low
SENSE
3
10
Sense resistor connection, low-side gate return
GLB
4
11
Gate driver
GLA
5
12
Gate driver
GHB
6
13
Gate driver
SB
7
14
High-side bridge reference
GHA
8
15
Gate driver
SA
9
16
High-side bridge reference
VCP
10
17
Charge pump reservoir cap connection
CP2
11
18
Charge pump terminal
VBB
12
19
Supply voltage
CP1
13
20
Charge pump terminal
GND
14
1
Ground
AIOUT
15
2
Analog output proportional to VSENSE
OCLn
16
3
OCP and OVP output flag, open drain
VREF
17
4
Analog OCP reference input
IN2
18
5
Digital IN2 input
IN1
19
6
Digital IN1 input
RC
20
7
Terminal to set blank- and off-time
PAD
–
–
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
3
A4955
Full-Bridge PWM Gate Driver
ELECTRICAL CHARACTERISTICS: Valid for Temperature Range G version at TJ = 25°C and
for Temperature Range K version at TJ = –40°C to 150°C, VBB = 5.5 to 50 V, unless otherwise specified
Characteristics
VBB Supply Current
Symbol
Test Conditions
IBB
IBB
SLEEPn = low, Standby Mode
Min.
Typ.
Max.
Unit
–
6
10
mA
–
–
5
µA
6.5
6.8
7.5
V
–
5.2
–
V
GATE DRIVE
High-Side Gate Drive Output
VGH
Low-Side Gate Drive Output
VGL
Gate Drive Pull-Up Current
Gate Drive Pull-Down Current
Dead-Time
Passive Pull-Down Resistance
Relative to VBB, IGATE = 200 µA, VBB = 8 to 50 V
Relative to VBB, IGATE = 200 µA, VBB = 5.5 V
IGATE = 200 µA, VBB = 8 to 50 V
6.5
6.8
7.5
V
IGATE = 200 µA, VBB = 5.5 V
–
5.4
–
V
IGPU
RISET = 30 kΩ; VGH = VGL = 4 V
21
30
39
mA
IGPD
RISET = 30 kΩ; VGH = VGL = 4 V
47
68
89
mA
tDT
–
1000
–
ns
RGPD
30
50
70
kΩ
LOGIC INPUT AND OUTPUT
Logic Output Voltage
VOCLn
I = 2 mA, overcurrent detected
–
0.2
0.3
V
Logic Output Leakage
IOCLn
V = 5 V, normal operation
–
–
5
µA
PWM Current Limit Flag Timer
tOCLn
300
500
600
µs
VIH
2.0
–
–
V
–
–
0.8
V
–
–
0.4
V
Logic Input Voltage
VIL
VIL(SLEEPn)
SLEEPn input
Logic Input Hysteresis
VHYS
–
320
–
mV
Logic Input Pull-Down Resistor
RPD
30
50
70
kΩ
VREF Input Current
IVREF
–5
VREF
OUTA
OUTB
Function
x
x
0
x
Z
Z
Sleep (Standby) Mode
0
0
1
x
Z
Z
Coast
0
1
1
false
L
H
Reverse
1
0
1
false
H
L
Forward
1
1
1
x
L
L
Slow Decay SR (Brake)
0
1
1
true
H/L
L
Internal Chop Reverse, Mixed Decay *
1
0
1
true
L
H/L
Internal Chop Forward, Mixed Decay *
* In fast decay, outputs change to high-Z state when load current approaches zero, to prevent reversal of current.
IOCL = VREF / RSENSE / 10
I_OUT
tOCLn
OCLn
OCLn Output Flag
OCLn output function is described in the Functional Description section.
A
A
B
B
C
300 µs
AIOUT
0V
VSENSE = VREF /10
V SENSE
0V
IN 1
(IN2 = High)
AIOUT Output
A. Internal OCL chop. AIOUT holds while SENSE voltage varies during the mixed-decay off-time.
B. INx chop. AIOUT holds while SENSE voltage drops to 0 V during slow decay.
C. Slow-decay timeout. AIOUT is forced to 0 V 300 µs after ENABLE goes low.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
5
A4955
Full-Bridge PWM Gate Driver
FUNCTIONAL DESCRIPTION
Device Operation
The A4955 is designed to operate DC motors. The output drivers
are capable of 50 V with gate-driver capability for an all N-channel external MOSFET H-bridge. Control logic includes synchronous rectification to reduce power dissipation. Current limit
is regulated by fixed off-time pulse-width-modulated (PWM)
control circuitry.
Internal PWM Current Control
Peak current is regulated by monitoring the voltage on an external sense resistor.
VREF
IPEAK =
(10 × RSENSE)
When the peak current is exceeded, the source driver turns off
for a fixed period tOFF to chop the current. The outputs operate
in mixed-decay mode during tOFF. Refer to the Fixed Off-Time
Setting section to set tOFF.
The internal current-sense circuit is ignored for tBLANK after
PWM transitions. The comparator output is blanked to prevent
false overcurrent detection due to reverse recovery currents of the
clamp diodes, or switching transients related to the capacitance of
the load, or both. Refer to the Blank-Time Setting section to set
tBLANK.
Brake
It is important to note that the internal PWM current-control
circuit will not limit the current when braking, since the current
does not flow through the sense resistor. The maximum current
can be approximated by VBEMF / RMOTOR. Care should be taken
to ensure that the maximum ratings of the external MOSFET are
not exceeded in worst-case braking situations of high speed and
high inertial loads.
ISET
A resistor from ISET terminal to ground sets the magnitude of
the gate current. The sink and source current ratios are fixed at
approximately 2-to-1 where the pull-down current is approximately two times the pull-up current. RISET should be between
15 and 150 kΩ.
The formula for determining the gate drive is:
IGATE_HS (mA) = 1.9 +
900
RISET (kΩ)
IGATE_LS (mA) = 3.5 +
1700
RISET (kΩ)
RC
The RC terminal is used to set both fixed off-time and blank-time
for the internal PWM current control. Refer to the following three
sections to select RC component values.
Fixed Off-Time Setting
The internal PWM current-control circuitry uses a one-shot to
control the time the drivers remain off. The one-shot off-time
(tOFF) is determined by the selection of an external resistor and
capacitor connected from the RC timing terminal to ground. The
off-time, over a range of values of CRC = 470 to 1500 pF and
RRC = 12 to 100 kΩ, is approximated by:
tOFF = RRC × CRC + dead time
Blank-Time Setting
This circuit blanks the output of the current-sense comparator
when the outputs are switched by the internal current-control
circuitry or by an external PWM chop command. The comparator
blanking time, tBLANK, is determined by the selection of an external resistor and capacitor connected from the RC timing terminal
to ground, and is approximated by:
(3.6/RRC (kΩ))
tBLANK = 2.6 µs × CRC (nF) × e
Slow Decay
In slow-decay mode, the low-side switch stays on and the
high-side switch turns off. Due to the synchronous rectification
feature, the complementary low-side switch turns on after a deadtime.
Fast Decay SR
In fast-decay mode, the high-side and low-side switches turn off,
and the complementary pair of switches is turned on, effectively
reversing the voltage polarity across the motor winding.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
6
A4955
Full-Bridge PWM Gate Driver
Mixed Decay
Charge Pump
When the peak current is reached, as set by the sense resistor and
voltage on VREF, the PWM current limiter initiates an off-time.
The off-time is determined by the resistor and capacitor on the
RC terminal. In mixed-decay mode, the driver will initiate a fast
decay, after a dead-time, for 13% of the programmed off-time.
After the fast-decay time expires, the bridge will switch to slow
decay for the remaining off-time. When the bridge is operating
in fast decay, it will internally prevent current reversal by putting
the bridge in a high-Z state if the current through the sense resistor falls close to zero.
The charge pump is used to generate a supply above VBB to
drive the high-side MOSFETs. The VCP voltage is internally
monitored and, in the case of a fault condition, the outputs of the
device are disabled.
OCLn Output
An open-drain logic output will be driven low to indicate system
operation. The OCLn terminal is driven low under two conditions:
1. When the system is limiting current to value set by VREF and
RSENSE. Once overcurrent events are no longer detected, the
A4955 will release the indication after a time tOCLn.
2. When a VDS fault is detected, the OCLn terminal is driven
low. It is released when the fault is reset.
The OCLn terminal, in combination with the AIOUT terminal,
can provide valuable information about how the system is behaving:
• Overcurrent events can indicate a motor stall condition, in
which case the system controller can respond to the fault
condition by reducing PWM duty. When OCLn is low and the
voltage on AIOUT is greater than 0 V, the controller is actively
limiting current with the internal, fixed off-time PWM current
limiter.
• In the case of a VDS fault, the OCLn terminal is also driven
low, but the AIOUT voltage will be 0 V, because the bridge
has been disabled. This notifies the user that a VDS fault has
occurred and the driver has been disabled.
AIOUT
An analog output can be used to monitor current through the
external sense resistor (if used). The SENSE voltage is gained by
a factor of 10 and fed to the AIOUT terminal. A sample-and-hold
circuit is used to capture the voltage across the sense resistor and
holds it during periods when the voltage is not representative of
the current in the motor. The AIOUT Output diagram illustrates
when the voltage is held. The held voltage will droop at a rate
equal to VDROOP. In the case of a VDS fault on the bridge, the
AIOUT terminal will be discharged to zero volts.
MOSFET VDS Protection
The drain-to-source voltage is monitored across the MOSFET
any time the MOSFET is on. If the voltage across the MOSFET
exceeds VDSTH, the bridge is disabled and latched off.
In order to prevent false VDS faults, the VDS monitor is blanked
immediately after any MOSFET is turned on. The VDS monitor
waits for a blank-time defined by the components on the RC terminal before monitoring the VDS level. During the off-time when
SR is active, VDS blanking is fixed at 1 μs.
VDS Fault
When a VDS fault occurs, and the bridge is disabled, and the
fault is latched, the OCLn terminal is immediately driven low.
The latch can only be reset by going into standby or by dropping
VBB below the UVLO threshold.
Standby Mode
Low power standby mode is activated when SLEEPn is brought
low. Standby mode disables most of the internal circuitry, including the charge pump and internal regulator. When coming out of
standby mode, the A4955 requires up to 300 μs before the outputs
can respond to input commands.
TSD
If the die temperature increases to approximately TTSD, the full
bridge outputs will be disabled until the internal temperature falls
below TTSD minus a hysteresis level of THYS.
Fault Shutdown
In the event of a fault due to excessive junction temperature,
or 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 until the UVLO thresholds are
exceeded.
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
7
A4955
Full-Bridge PWM Gate Driver
TERMINAL CIRCUIT DIAGRAMS
SX
VCP
6.7 V
GND
10 V
GND
VCP
GHX
VBB
GLX
IN1
IN2
RISET
AIOUT
VREF
SLEEPn
RC
OCLn
8V
6.7 V
GND
GND
SX
SENSE
CP2
CP1
VCP
8V
GND
VBB
GND
GND
SENSE
VBB
56 V
GND
8V
GND
GND
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
8
A4955
Full-Bridge PWM Gate Driver
PACKAGE OUTLINE DRAWINGS
For Reference Only – Not for Tooling Use
(Reference Allegro DWG-0000222 Rev. 4 or JEDEC MO-220WGGD)
Dimensions in millimeters – NOT TO SCALE
Exact case and lead configuration at supplier discretion within limits shown
0.30
0.50
4.00 BSC
20
20
1
0.95
A
1
2×
2
2
2.45
4.10
0.15
C
4.00 BSC
0.15
C
2×
2.45
21×
D
0.08
C
C
SEATING
PLANE
0.75 ±0.05
+0.03
0.02 –0.02
+0.05
0.25 –0.07
4.10
C
PCB Layout Reference View
0.50 BSC
1
XXXX
Date Code
Lot Number
0.40 ±0.10
B
2.45 ±0.10
2
E
1
Standard Branding Reference View
0.20 MIN
20
2.45 ±0.10
A
Line 1: Part Number
Line 2: 4 digit Date Code
Line 3: Characters 5, 6, 7, 8 of
Assembly Lot Number
Pin 1 Dot top left
Center align
Terminal #1 mark area
B
Exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion)
C
Reference land pattern layout (reference IPC7351 QFN50P400X400X80-21BM); 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
E
Branding scale and appearance at supplier discretion.
ES Package, 20-Pin QFN with Exposed Thermal Pad
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
9
A4955
Full-Bridge PWM Gate Driver
For Reference Only – Not for Tooling Use
(Reference JEDEC MO-153ACT; Allegro DWG-0000379, Rev. 3)
NOT TO SCALE
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
6.50 ±0.10
0.45
4.20
8°
0°
20
0.65
20
0.20
0.09
1.70
C
3.00
4.40 ±0.10
3.00
6.40 ±0.20
A
6.10
1.00 REF
0.60 ±0.15
1
2
1
0.25 BSC
20X
0.10
1.20 MAX
C
0.30
0.19
C
2
4.20
SEATING PLANE
GAUGE PLANE
SEATING
PLANE
B
PCB Layout Reference View
0.15
0.025
0.65 BSC
XXXXXXX
Date Code
Lot Number
A
Terminal #1 mark area
B
Reference land pattern layout (reference IPC7351 SOP65P640X110-21M); 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)
C
Exposed thermal pad (bottom surface)
D
Branding scale and appearance at supplier discretion
1
D
Standard Branding Reference View
Line 1: Part Number
Line 2: Logo A, 4 digit Date Code
Line 3: Characters 5, 6, 7, 8 of Assembly Lot Number
LP Package, 20-Pin eTSSOP with Exposed Thermal Pad
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
10
A4955
Full-Bridge PWM Gate Driver
Revision History
Revision
Revision Date
–
February 12, 2015
1
July 14, 2015
2
November 30, 2017
3
January 11, 2019
Description of Revision
Initial Release
Updated functional block diagram (page 1); added packing information (page 2); changed
references to LSS to SENSE
Updated ISET section (page 6)
Minor editorial updates
4
July 1, 2019
Updated A4955KLPTR-T product variant status to Not for New Design
5
July 18, 2022
Updated package drawings (pages 9-10)
Copyright 2022, Allegro MicroSystems.
Allegro MicroSystems 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 any devices or systems, including but not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems assumes no responsibility for its use; nor
for any infringement of patents or other rights of third parties which may result from its use.
Copies of this document are considered uncontrolled documents.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
11
