A4915 Datasheet

A4915
3-Phase MOSFET Driver
Description
Features and Benefits
•5 to 50 V supply voltage
•Latched TSD with fault output
•Drives six N-channel high current MOSFETs
•Internally controlled synchronous rectification
•Speed voltage input enables internal PWM duty cycle
control of full bridge
•Center aligned PWM
•Internal UVLO and crossover current protection
•Hall switch inputs
•Adjustable dead time protection
•Low power sleep mode for battery-powered applications
The A4915 is designed for pulse width modulated (PWM)
current control of 3-phase brushless DC motors. The A4915
is capable of high current gate drive for 6 all N-channel power
MOSFETs. An internal charge pump ensures gate drive down
to 7 V supply and provides limited gate drive down to 5 V. A
bootstrap capacitor is used to generate a supply voltage greater
than the source voltage of the high side MOSFET, required
for N-channel MOSFETs.
Internal synchronous rectification control circuitry is provided
to improve power dissipation in the external MOSFETs during
PWM operation. Internal circuit protection includes latched
thermal shutdown, dead time protection, and undervoltage
lockout. Special power up sequencing is not required.
Packages:
28-pin TSSOP
with exposed thermal pad
(LP package)
The A4915 is supplied in a 28-pin TSSOP with an exposed
thermal pad (suffix LP) and a 28-contact 5 × 5 mm QFN with
an exposed thermal pad (suffix ET). These packages are lead
(Pb) free, with 100% matte-tin leadframe plating.
28-contact QFN
5 mm × 5 mm × 0.90 mm
(ET package)
Not to scale
VDD
Comm
Logic
HA
HB
0.47 µF
CP1
CP2
Functional Block Diagram
Charge Pump
Regulator
A4915
VBB
VIN
CREG
VREG
47 V
TVS
CVBB1
CVBB2
HC
VDD
VDD
TDEAD
Control
Logic
Voltage to
Duty
VRESET
FAULT
A4915-DS, Rev. 4
RGATE
SB
SC
GLA
GLB
OSC
SPEED
R3
HA
HB
HC
CBOOTA
SA
VREG
VDD
CA
CB
CC
GHA
GHB
GHC
DIR
ENABLE
R2
R1
High Side
Driver
BRAKEn
Rdead
Phase A
Bootstrap
Monitor
CVDD1
Low Side
Driver
RGATE
To Phase B
To Phase C
GLC
One of three phases shown
LSS
GND
A4915
3-Phase MOSFET Driver
Selection Guide
Part Number
Package
Packing*
A4915METTR-T
28-contact QFN with
exposed thermal pad
1500 pieces
per 7-in. reel
A4915MLPTR-T
28-pin TSSOP with
exposed thermal pad
4000 pieces
per 13-in. reel
Absolute Maximum Ratings
Characteristic
Symbol
Notes
Rating
Unit
Load Supply Voltage
VBB
–0.3 to 50
V
Logic Supply Voltage
VDD
–0.3 to 6
V
VREG Pin
VREG
–0.3 to 16
V
CP1 Pin
VCP1
–0.3 to 16
V
CP2 Pin
VCP2
VCP1 – 0.3 to
VREG + 0.3
V
VI
–0.3 to 6
V
Logic Inputs
Hall Inputs
VHx
–0.3 to 6
V
Logic Outputs
VO
–0.3 to 6
V
SPEED Input
VSPEED
–0.3 to 6
V
CA, CB, and CC Pins
VCx
–0.3 to
VREG + 50
V
GHA, GHB, and GHC Pins
VGHx
VCx – 16 to
VCX + 0.3
V
VSx
VCx – 16 to
VCx + 0.3
V
SA, SB, and SC Pins
GLA, GLB, GLC Pins
VGLx
VREG – 16 to 18
V
LSS Pin
VLSS
VREG – 16 to 18
V
TJ(max)
150
°C
Storage Temperature Range
Tstg
–55 to 150
°C
Operating Ambient Temperature
Range
TA
–20 to 105
°C
Maximum Continuous Junction
Temperature
Thermal Characteristics may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance
Symbol
RθJA
Test Conditions*
Value
Unit
Package ET, on 4-layer PCB based on JEDEC standard
32
ºC/W
Package LP, on 4-layer PCB based on JEDEC standard
28
ºC/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4915
3-Phase MOSFET Driver
22 GHA
23 SA
24 CA
25 VREG
26 CP2
27 CP1
28 GND
Pin-out Diagrams
LSS 1
28 HC
GLC 2
27 HB
GHC 3
26 HA
VBB
1
21 GLA
SC 4
25 BRAKEn
SPEED
2
20 CB
CC 5
24 DIR
TDEAD
3
19 SB
GLB 6
VDD
4
18 GHB
GHB 7
17 GLB
SB 8
21 VDD
CB 9
20 TDEAD
GLA 10
19 SPEED
GHA 11
18 VBB
SA 12
17 GND
CA 13
16 CP1
VREG 14
15 CP2
FAULT
PAD
5
GHC 14
GLC 13
LSS 12
BRAKEn
HC 11
15 SC
HB 10
16 CC
7
8
6
DIR
HA 9
ENABLE
ET Package
PAD
23 ENABLE
22 FAULT
LP Package
Terminal List Table
Name
VBB
SPEED
TDEAD
VDD
FAULT
ENABLE
DIR
BRAKEn
Function
Number
ET
LP
Name
Function
Number
ET
LP
Supply voltage
1
18
SC
High-side source connection
15
4
Reference voltage input
2
19
CC
Bootstrap output phase C
16
5
Terminal for dead time setting
3
20
GLB
Low-side gate drive
17
6
Logic supply input
4
21
GHB
High-side gate drive
18
7
Fault output
5
22
SB
High-side source connection
19
8
Logic input, PWM control
6
23
CB
Bootstrap output phase B
20
9
Logic input, motor direction
7
24
GLA
Low-side gate drive
21
10
Logic input, motor brake (active low)
8
25
GHA
High-side gate drive
22
11
HA
Hall input phase A
9
26
SA
High-side source connection
23
12
HB
Hall input phase B
10
27
CA
Bootstrap output phase a
24
13
HC
Hall input phase C
11
28
VREG
Gate drive supply output
25
14
LSS
Sense input
12
1
CP2
Charge pump capacitor terminal
26
15
GLC
Low-side gate drive
13
2
CP1
Charge pump capacitor terminal
27
16
GHC
High-side gate drive
14
3
GND
Ground
28
17
PAD
Exposed pad for enhanced thermal dissipation
–
–
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4915
3-Phase MOSFET Driver
ELECTRICAL CHARACTERISTICS Valid at TA = 25°C, VBB = 24 V; unless otherwise specified
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Supply and Reference
Operating Voltage Range
Motor Supply Current
VBB
IBB
Operating, outputs active
5.0
–
50
V
fENB = 30 kHz, CLOAD = 10 nF
–
10
20
mA
fPWM ≈ 20 kHz, CLOAD = 10 nF
–
12
24
mA
VREG = 13 V, outputs disabled
–
3
3.5
mA
Sleep mode
–
–
1
µA
ID = 10 mA
0.4
0.7
1.0
V
ID = 100 mA
1.5
2.2
2.8
V
Bootstrap Diode Forward Voltage
VfBOOT
Bootstrap Diode Current Limit
VDBOOT
250
500
750
mA
VDD
3
–
5.5
V
VDD Input Voltage
VDD Input Current
IDDQ
ENABLE = high, outputs disabled
–
6
10
mA
IDDS
Sleep mode
–
–
10
µA
ENABLE = low for longer than tSLEEP,
SPEED = high
–
–
1
µA
ENABLE = high,
SPEED = low for longer than tSLEEP
–
–
1
µA
–
–
1
µA
ENABLE Input Current Sleep Mode
IENB(SLP)
SPEED Input Current Sleep Mode
ISPEED(SLP)
BRAKEn Input Current Sleep Mode
IBRAKE(SLP) ENABLE = low for longer than tSLEEP
DIR Input Current Sleep Mode
ENABLE Input Frequency Range
Internal PWM Frequency
SPEED Input Voltage Range
IDIR(SLP)
ENABLE = low for longer than tSLEEP
–
–
1
µA
fENB
VSPEED = VDD
1
–
100
kHz
fPWM
VENABLE = VDD
14
20
26
kHz
0
–
VDD
V
VSPEED
SPEED Disable Voltage
VSPEED(D)
Measured as VSPEED / VDD , duty cycle = 0%
10
15
20
%
SPEED Enable Voltage*
VSPEED(E)
Measured as VSPEED / VDD , duty cycle = 100%
79
82
86
%
SPEED Bias Current
ISPEED(bias) VSPEED = VDD= 5 V
VBB = 9 V
VREG Output Voltage
VREG
VBB = 7.5 V
–25
0
25
µA
11.8
13
13.75
V
11.5
13
13.75
V
2 × VBB
– 3.5 V
–
–
V
VBB = 5.5 V
8.0
9.5
–
V
VBB = 6 V
Protection
Thermal Shutdown Temperature
VREG Undervoltage
VREG Undervoltage Hysteresis
TTSD
FAULT rising
155
170
185
°C
VREGON
VREG rising
7.0
7.8
8.6
V
VREGOFF
VREG falling
6.39
7.1
7.81
V
–
700
–
mV
VREGhys
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
A4915
3-Phase MOSFET Driver
ELECTRICAL CHARACTERISTICS (continued) Valid at TA = 25°C, VBB = 24 V; unless otherwise specified
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Protection (continued)
Bootstrap Undervoltage
Bootstrap Undervoltage Hysteresis
VDD Undervoltage
VDD Undervoltage Hysteresis
Sleep Wake-up Delay
VBOOTUV
Measured as a percentage of VREG
55
–
65
%
VBOOTUVhys Measured as a percentage of VREG
–
20
–
%
VDD rising
–
2.75
2.95
V
VDD falling
2.45
2.6
–
V
VDDUVhys
50
100
150
mV
tWAKE
–
–
3
ms
VCx – 0.2
–
–
V
–
–
VSx + 0.3
V
VREG – 0.2
–
–
V
–
–
0.3
V
VDDUV
Gate Drive
High-Side Gate Drive Output
VGHx
Low-Side Gate Drive Output
VGLx
CBOOTx fully charged, CLOAD = 10 nF
IGHx < 10 µA
VREG = 13 V, CLOAD = 10 nF
IGLx < 10 µA
TJ = 25°C, IGHx = –150 mA
6
9
12
Ω
TJ = 125°C, IGHx = –150 mA
–
17
–
Ω
TJ = 25°C, IGLx = –150 mA
2.4
3.5
4.6
Ω
TJ = 125°C, IGLx = –150 mA
–
5
–
Ω
Gate Drive Pull-Up Resistance
RGHx(ON)UP
Gate Drive Pull-Down Resistance
RGLx(ON)DN
GHx Passive Pull-Down
RGHx(PPD)
VGHx – VSx < 0.3 V
–
5000
–
Ω
GLx Passive Pull-Down
RGLx(PPD)
VGLx – VLSS < 0.3 V
–
5000
–
Ω
trGx
20% to 80%, CLOAD = 10 nF
–
200
–
ns
tfGx
80% to 20%, CLOAD = 10 nF
Output Switching Time
TDEAD tied to GND
Dead Time
tDEAD
Time delay measured
from turn-off to turn-on
–
150
–
ns
10
–
–
ns
RTDEAD = 12 kΩ
–
150
–
ns
RTDEAD = 64 kΩ
800
925
1050
ns
RTDEAD = 220 kΩ
–
2.9
–
µs
0.7 × VDD
–
–
V
–
–
0.3 × VDD
V
Logic I/O
Logic Input Voltage
Logic Input Current
VIN(H)
VIN(L)
BRAKEn, DIR, ENABLE, HA, HB, and HC pins
IIN(H)
VIN = high
–
10
–
µA
IIN(L)
VIN = low, ENABLE = low
–1
0
1
µA
No fault present, ISINK = 1mA
–
–
0.2
V
ENABLE = low, SPEED = high
1
2
3
ms
ENABLE = high, SPEED = low
1
2
3
ms
FAULT Output Voltage
VFAUlT
ENABLE and SPEED Sleep Timer
tSLEEP
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
5
A4915
3-Phase MOSFET Driver
ELECTRICAL CHARACTERISTICS (continued) Valid at TA = 25°C, VBB = 24 V; unless otherwise specified
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Logic I/O (continued)
SPEED Sleep Threshold
Fault Latch Reset Voltage
Fault Latch Reset Pulse Time
Hall Input Pull-Up Resistor
Hall Input Current
VSPEEDSLPth SPEED = low for longer than tSLEEP
–
–
295
mV
VRESET
Fault is present, outputs latched
–
–
0.8
V
tFAULT
Fault is present, outputs latched
12
–
–
µs
RHx(PU)
Hx pins, VIN = 0 V
–
100
–
kΩ
IHALL
Hx pins, VIN = 5 V
–
0
1
µA
Logic Input Pull-Down Resistor
RIN(PD)
ENABLE, DIR, BRAKEn, VIN = 5 V
–
50
–
kΩ
Login Input Current Sleep Mode
IIN(SLP)
ENABLE, DIR, BRAKEn
–
–
1
µA
tpd(on)
DIR or BRAKEn input to output change,
CLOAD = 0 nF
–
–
1200
ns
ENABLE input to output change, CLOAD = 0 nF
–
–
900
ns
DIR or BRAKEn input to output change,
CLOAD = 0 nF
–
–
1200
ns
ENABLE input to output change, CLOAD = 0 nF
–
–
900
ns
ENABLE
–
–
900
ns
DIR, BRAKEn
–
–
1000
ns
Propagation Delay
tpd(off)
Input Pin Glitch Reject
tglitch
*Output duty cycle limited by tDEAD .
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
A4915
3-Phase MOSFET Driver
Functional Description
from the supply. When coming out of sleep allow 3 ms for the
charge pump regulator to stabilize.
Basic Operation
The A4915 is a 3-phase MOSFET driver intended to drive high
current MOSFETs. It is designed for use in battery operated
equipment where low-voltage operation is critical. The A4915
also features a low current sleep mode which disables the device
and draws minimum supply current. The A4915 is capable of
driving 6 N-channel MOSFETs. Commutation logic includes
Enable, Direction, and Brake modes for external PWM control.
SPEED The duty cycle of the internally generated carrier fre-
A Speed input is provided which allows an external source to
PWM the bridge at 30 kHz typical. The PWM duty cycle is
controlled by applying an analog voltage to the SPEED pin from
0 V to VDD .
Pin Descriptions
DIR The Direction pin is used to change the commutation direc-
tion of the 3 bridges. Refer to Table 1 for phase commutation
information.
ENABLE The ENABLE input terminal allows external PWM
control. Setting ENABLE high turns on the selected sink-source
pair, and setting it low switches off the appropriate drivers and
the load current decays. If external PWM is used, the SPEED pin
must be tied to VDD.
When the ENABLE input is held low for longer than tSLEEP the
A4915 turns off all internal circuitry and draws minimum current
quency is controlled by applying a DC voltage on the SPEED
input. A plot showing the relationship of Speed to duty cycle is
shown in Figure 1. When SPEED is pulled directly to VDD the
internal carrier is disabled and the Enable input can be used to
PWM the bridge. When VSPEED < VSPEED(D) the output is guaranteed to be 0%. When VSPEED > VSPEED(E) the output is guaranteed to be 100%.
BRAKEn Brake mode turns all three sink drivers on and effectively shorts out the motor generated BEMF. The BRAKEn input
overrides the ENABLE and SPEED inputs except when in Sleep
mode. Refer to Table 2 for the logic truth table. In order to comply with Failure Mode Effects and Analysis (FMEA), the brake
function is normally active (logic low). If the BRAKEn pin on
the device is open due to some failure of solder joint or microprocessor failure, the device will automatically implement Brake
mode, preventing the motor from turning or pumping up the
supply. Applying logic high to the BRAKEn terminal deactivates
Brake mode and allows normal operation.
Care must be taken when applying the Brake command because
large currents can be generated. The user must ensure that the
maximum ratings of the MOSFETs are not exceeded under worst
Table 1: Commutation Table
HA
HB
HC
DIR
GLA
GLB
GLC
GHA
GHB
GHC
SA
SB
SC
1
1
0
1
1
0
0
1
1
0
0
2
1
0
0
1
0
0
1
0
1
0
High
–
Low
–
High
Low
3
1
1
0
1
1
0
0
0
1
4
0
1
0
1
1
0
0
0
0
0
Low
High
–
1
Low
–
High
5
0
1
1
1
0
1
0
0
0
6
0
0
1
1
0
1
0
1
0
1
–
Low
High
0
High
Low
–
1
1
0
1
0
1
0
0
0
2
1
0
0
0
0
1
0
0
0
1
Low
–
High
0
1
–
Low
High
3
1
1
0
0
0
1
0
4
0
1
0
0
0
0
1
1
0
0
High
Low
–
1
0
0
High
–
Low
5
0
1
1
0
0
0
1
0
1
0
–
High
Low
6
0
0
1
0
1
0
0
0
1
0
Low
High
–
Hall Fault
1
1
1
X
0
0
0
0
0
0
–
–
–
Hall Fault
0
0
0
X
0
0
0
0
0
0
–
–
–
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
A4915
3-Phase MOSFET Driver
case braking conditions. Maximum motor current during Brake
mode can be approximated by:
100
90
IBRAKEn = VBEMF / RL
80
where VBEMF is the voltage generated by the motor and RL is the
resistance of the phase winding.
FAULT The Fault output is active high. Under normal operation
(%)
low‑side gate drivers and to charge the bootstrap capacitors.
60
Ton / T
VREG A regulated voltage output that is used to supply the
70
50
40
the open drain output pulls the Fault output to ground. When
a fault occurs the open drain output is released, and the Fault
output is then pulled to a logic high through a connected external
passive pullup resistor. Fault conditions are shown in Table 3.
30
20
The presence of an invalid Hall combination is referred to as a
Hall Fault. Invalid Hall combinations are documented in Table 1.
When a Hall Fault is present, the outputs are disabled. Invalid
Hall Faults are not latched, and do not affect the state of the
FAULT pin. Latched faults that result in disabled outputs can be
reset in a number of ways:
•A UVLO on VDD will serve as a reset
10
10
0
20
30
40
50
60
70
80
90
100
VSPEED/VDD (%)
Figure 1: Speed in Relation to Duty Cycle
Table 3: Fault Conditions
•If the device is put into sleep mode the latch is reset
•A microprocessor can create a reset on the FAULT pin directly
by forcing VRESET on the FAULT pin when a fault is active for
longer than tFAULT (that is, when the outputs are latched)
LSS The LSS terminal is the low-side drain connection for the
Event
Fault Pin
TSD
High
Outputs Latched
Disabled
Yes
SLEEP
High
Disabled
No
UVLO VREG/VDD
High
Disabled
No
Invalid Hall
Low
Disabled
No
MOSFET. If an external PWM current control loop is used, a low
Table 2: Input Logic Truth Table
Inputs
Mode of Operation
ENABLE
SPEED
BRAKEn
Low
High
High
PWM chop slow decay synchronous rectification (center aligned)
Low
High
Low
Brake mode – All low-side gates on
High
High
High
Selected drivers onb
High
High
Low
Brake mode – All low-side gates on
High
VDD × VSPEED(E) to
VDD × VSPEED(D)
High
PWM chop slow decay synchronous rectification (center aligned)c
High
> VDD × VSPEED(E)
High
Selected drivers onb
High
< VDD × VSPEED(D)
High
PWM chop slow decay synchronous rectification (center aligned)
Low longer than tSLEEP
High
Xa
Sleep mode – coast
High
Low longer than tSLEEP
Xa
Sleep mode – coast
aX
= don’t care.
and minium duty cycle limited by boot capacitor charge management.
cInternal PWM active.
bMaximum
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A4915
3-Phase MOSFET Driver
value sense resistor can be placed from LSS to ground for current
sensing purposes. The resistor should be chosen so that the DC
voltage across the sense resistor is between 200 mV and
500 mV. If a sense resistor is not used then LSS should be connected directly to power ground.
time resistor (RDEAD) between the TDEAD pin and ground.
CA, CB, CC High-side connections for the bootstrap capacitors
(CBOOTx) and positive supply for high-side gate drive.
Current, IDEAD, can be calculated by:
GHA, GHB, GHC High-side gate drive outputs for N-channel
MOSFETs.
SA, SB, SC Motor phase connections, serve as the negative supplies for the high-side gate drive.
GLA, GLB, GLC Low-side gate drive outputs for N-channel
MOSFETs.
CP1, CP2 Connections for the charge pump switching capacitor.
Typical capacitance should be 0.47 µF.
For RDEAD values between 12 and 220 kΩ, at 25°C the nominal
value of tDEAD in ns can be approximated by:
tDEAD = 40 + (1.28 × 10–2 × RDEAD)
IDEAD = 1.2 / RDEAD
As values for R increase, current offsets and resistor mismatch
cause the error terms to increase. Figure 2 shows the typical
expected error for a given RDEAD value.
Sleep Mode
The A4915 has a low-current Sleep mode to limit current draw on
the battery. When in low-current Sleep mode (when ENABLE =
low for longer than tSLEEP and SPEED = high), current into VBB
and VDD is less than 1 μA.
When ENABLE is held low for longer than tSLEEP and the
SPEED input is held high, the pull-up resistors on the Hall inputs
and the pull-down resistor on the BRAKEn pin are open-circuited
to minimize current draw into logic input terminals. Only the
condition where SPEED = high and ENABLE = low for longer
than tSLEEP results in low current on logic input terminals.
HA, HB, HC Hall input connections from Hall switches at the
motor.
Thermal Shutdown
If the die temperature exceeds TTSD , the FAULT output is
turned off and the outputs are disabled. Thermal shutdown is a
latched fault.
Dead Time
To prevent cross-conduction (shoot through) in any phase of the
bridge, it is necessary to have a dead time, tDEAD , between a
high- or low-side turn-off and the next complementary turn-on
event. The dead time for all three phases is set by a single dead
Center Aligned PWM
The A4915 features center aligned PWM, which improves
power dissipation and helps reduce EMI. During an off-time
triggered by either an internal PWM or by an external Enable
chop command, current recirculation will be in either the highside FETs or the low-side FETs, depending on the state of an
internal latch. On each bridge Enable command, the latch is reset
4000
3500
Maximum
Dead Time (ns)
3000
Typical
2500
Minimum
2000
1500
1000
500
0
10
30
50
70
90
110
130
150
170
190
210
230
250
RDEAD (kΩ)
Figure 2: RDEAD versus Dead Time Error
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A4915
and the current recirculation shifts from high-side recirculation to
low‑side recirculation.
This method of recirculation shifts 50% of the power to the
high‑side drivers during the off-time, reducing the power dissipation in the sink drivers. Reducing the overall temperature of the
output drivers by sharing power between the 6 FETs improves
system efficiency and battery life.
Internal/External PWM
The A4915 can be pulse width modulated (PWM) to control current. There are two methods by which PWM can be applied to the
device.
•External PWM. This method requires a PWM signal be applied
to the ENABLE pin. When the SPEED pin is tied directly to
VDD, the ENABLE pin can be chopped from 0 to 100%. If the
ENABLE input is held low for more than sleep timer, tSLEEP ,
the device enters low current sleep mode.
•Internal PWM. This method uses the internally generated PWM,
which is controlled by applying a DC voltage to the SPEED pin.
When the ENABLE pin is tied directly to VDD, the speed can
be controlled from 0 to 100%. See the SPEED pin description
for further information.
For complete description of all operating conditions, see Table 2.
Synchronous Rectification
When a PWM off-time cycle is triggered by an ENABLE chop
command or by an internal PWM off-time, load current recirculates. The A4915 synchronous rectification feature will turn on
the appropriate MOSFETs during the off-time and effectively
short out the body diodes with the low RSD(on) driver. This will
lower power dissipation significantly and eliminates the need for
external Schottky diodes.
Charge Pump Regulator
The gate drives for the low-side MOSFETs and the bootstrap
charge for the high-side drivers is accomplished by the charge
pump regulator. For VBB above 16 V, the regulator acts as a linear
regulator. Below 16 V, the regulated supply is maintained by
a charge pump boost converter that requires a pump capacitor
between CP1 and CP2.
3-Phase MOSFET Driver
The regulated voltage VREG is decoupled on the VREG terminal. The decoupling capacitance is based on the bootstrap capacitor which is dependent on the MOSFET selection. Refer to the
Application Information section for details on correct sizing of
VREG and bootstrap capacitors.
Gate Drive and RGATE
The gate drive for the external MOSFETs is capable of providing
the large current transients needed to quickly charge and discharge the gate capacitance to maintain fast switching speeds and
minimal power dissipation. The low-side driver current is sourced
by the capacitor on the VREG terminal. The high-side gate drive
current is supplied by the respective bootstrap capacitance connected between the Cx and Sx terminals. The charge and discharge of the gate can be controlled by using an external resistor
(RGATE) in series with the gate.
Bootstrap Charge Management
In order to protect the external MOSFETs from insufficient gate
drive, it is important that the bootstrap capacitor voltage be monitored. Before a high-side switch is allowed to turn on, it must
have sufficient charge on the bootstrap capacitor. If the voltage
on the bootstrap capacitor is below the turn-on voltage limit, the
A4915 will attempt to charge the bootstrap capacitor by turning
on the associated low-side driver. The bootstrap monitor stays
active during the duration of the switch on-time. If the voltage
falls out of compliance at any time when the high-side driver is
enabled, the driver is disabled and the low-side switch is activated to charge the bootstrap capacitor.
During normal operation and in conditions where the PWM
duty cycle creates short off-times, the low-side switch may be
activated more often to keep sufficient charge on the bootstrap
capacitor. Proper sizing of the bootstrap and VREG capacitors is
critical to being able to maintain effective gate drive. Refer to the
Application Information section for details on correct sizing of
VREG and bootstrap capacitors.
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A4915
3-Phase MOSFET Driver
Application Information
Bootstrap Capacitor Selection
In order to properly size the capacitor CBOOT, the total gate
charge must be known. Too large a bootstrap capacitor and the
charge time will be long, resulting in maximum duty cycle limitation. Too small a capacitor and the voltage ripple will be large
when charging the gate.
Size the CBOOT capacitor such that the charge, QBOOT, is 20
times larger than the required charge for the gate of the MOSFET,
QGATE:
CBOOT = (QGATE × 20) / VBOOT
where VBOOT is the voltage across the bootstrap capacitor. The
voltage drop across the bootstrap capacitor as the MOSFET gate
is being charged, ΔV, can be approximated by:
ΔV = QGATE / CBOOT
For the bootstrap capacitor, a ceramic type rated at 16 V or larger
should be used.
VREG Capacitor Selection
VREG is responsible for providing all the gate charge for the low
side MOSFETs and for providing all the charge current for the
three bootstrap capacitors. For these purposes, the VREG capacitor, CREG , should be 20 times the value of CBOOT:
CREG = 20 × CBOOT
Layout Recommendations
Careful consideration must be given to PCB layout when designing high frequency, fast-switching, high-current circuits (refer to
Figures 3 and 4):
•The A4915 ground, GND, and the high-current return of the external MOSFETs should return separately to the negative side of
the motor supply filtering capacitor. This minimizes the effect
of switching noise on the A4915.
•The exposed thermal pad should be connected to GND.
•Minimize stray inductance by using short, wide copper traces
at the drain and source terminals of all power MOSFETs. This
includes motor lead connections, the input power bus, and the
common source of the low-side power MOSFETs. This minimizes voltages induced by fast switching of large load currents.
•Consider the use of small (100 nF) ceramic decoupling capacitors across the source and drain of the power MOSFETs, to limit
fast transient voltage spikes caused by inductance in the traces.
•Keep the gate discharge return connections Sx and LSS as short
as possible. Any inductance on these traces causes negative
transitions on the corresponding A4915 terminals, which may
exceed the Absolute Maximum Ratings. If this is likely, consider the use of clamping diodes to limit the negative excursion
on these terminals with respect to GND.
•Supply decoupling for VBB, VREG, and VDD should be connected independently, close to the GND terminal. The decoupling capacitors should also be connected as close as possible to
the relevant supply terminal.
•Gate charge drive paths and gate discharge return paths may
carry large transient current pulses. Therefore the traces from
GHx, GLx, Sx (x = A, B, or C) and LSS should be as short as
possible to reduce the inductance of the trace.
•Provide an independent connection from LSS to the common
point of the power bridge. This can be the negative side of the
motor supply filtering capacitor or one end of a sense resistor. It
is not recommended to connect LSS directly to the GND terminal, as this may increase the noise at the digital inputs.
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A4915
3-Phase MOSFET Driver
VBB
GND
R1 R7
C2
Q1
PHASE A
R4 R10
C4
C7
C6
Q4
C8
GND
VBB
GND
R24
C5
R2
C9
R15
R8
Q2
C10
PHASE B
R5 R11
C1
Q5
VBB
R3 R9
Q3
GND
D1
PHASE C
R6 R12
Q6
LSS
VDD
ET Package Typical PCB Layout
C8
Solder
C6
Thermal (2 oz.)
SPEED
TDEAD
Thermal Vias
R4
GLA
R10
R7
Q1
C2
Q4
A4915
OUTA
CB
R24
PAD
ET Package Schematic Corresponding
to Typical PCB Layout
CA
SA
GHA
VREG
C4
CP1
VBB
Ground (1 oz.)
CP2
Signal (1 oz.)
C9
SB
GHB
VDD
R2
C5
GLB
FAULT
R8
Q2
VBB
R5
R11
Q5
R15
ENABLE
DIR
BRAKEn
HA
HB
HC
LSS
GLC
GHC
PCB
R1
Trace (2 oz.)
GND
A4915
OUTB
CC
SC
C10
R3
R9
Q3
C1
R6
R12
Q6
OUTC
VDD
Figure 3: Typical Application Information for ET Package
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A4915
3-Phase MOSFET Driver
VDD
LSS
Q6
R12 R6
Q3
R9
Q5
R11 R5
PHASE C
D1
GND
C1
R3
PHASE B
C10
Q2
R8
R15
C5
C9
R2
C4
C8
GND
VBB
R24
GND
C7
C6
Q4
R10 R4
Q1
R7
PHASE A
R1
GND
C2
LP Package Typical PCB Layout
VDD
OUTC
LSS
GLC
Q6
R12
HC
HB
HA
BRAKEn
DIR
ENABLE
R6
C1
Q3
R9
R3
C10
GHC
SC
CC
OUTB
A4915
A4915
Solder
Q5
Trace (2 oz.)
PCB
R11
R5
PAD
Signal (1 oz.)
VBB
Ground (1 oz.)
Q2
Thermal (2 oz.)
R8
R2
VDD
C5
R24
GHB
SB
TDEAD
CB
SPEED
C9
OUTA
R15
FAULT
GLB
Thermal Vias
VBB
LP Package Schematic Corresponding to
Typical PCB Layout
C4
GLA
Q4
Q1
C2
R7
R10
R4
R1
GHA
SA
GND
CA
CP1
VREG
CP2
C8
C6
Figure 4: Typical application information for LP package
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A4915
3-Phase MOSFET Driver
Input / Output Structures
VBB
VDD
VREG
FAULT
CP1
6V
18V
6V
50 kΩ
18V
14V
Figure 5: Supplies
2 kΩ
BRAKE
DIR
ENABLE
18V
18V
VDD
CP2
Figure 6:
Fault Output
6V
Figure 7: Charge Pump
6V
Figure 8: Logic Inputs with Pull-down:
BRAKEn, DIR, ENABLE
Cx
18V
VDD
VDD
50 kΩ
HA
HB
HC
18V
GHx
14V
Sx
5 kΩ
SPEED
2 kΩ
6V
VDD
18V
VREG
6V
6V
6V
18V
18V
GLx
LSS
Figure 9: Hall inputs with pull-up:
HA, HB, HC
Figure 10: Gate Drive Outputs
Figure 11: Speed Input
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A4915
3-Phase MOSFET Driver
Package ET, 28-Pin QFN
with Exposed Thermal Pad
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
+0.05
0.25 –0.07
0.90 ±0.10
C
4.80
C
PCB Layout Reference View
0.50
For Reference Only; not for tooling use
(reference JEDEC MO-220VHHD-1)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
0.73 MAX
B
2
1
28
3.15
3.15
A Terminal #1 mark area
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
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15
A4915
3-Phase MOSFET Driver
Package LP, 28-Pin TSSOP
with Exposed Thermal Pad
0.45
9.70±0.10
8º
0º
28
0.65
28
0.20
0.09
1.65
B
3 NOM
4.40±0.10
3.00
6.40±0.20
6.10
0.60 ±0.15
A
1
2
1.00 REF
5.08 NOM
0.25 BSC
Branded Face
28X
SEATING
PLANE
0.10 C
0.30
0.19
0.65 BSC
SEATING PLANE
GAUGE PLANE
C
1 2
5.00
C
PCB Layout Reference View
For Reference Only; not for tooling use (reference 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
1.20 MAX
0.15
0.00
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)
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115 Northeast Cutoff
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16
A4915
3-Phase MOSFET Driver
Revision History
Revision
Current
Revision Date
1
April 1, 2013
2
March 6, 2014
Update Absolute Maximum Ratings table and content on page 9
3
April 25, 2014
Revised Schematics on pp. 12 and 13
4
March 10, 2015
Description of Revision
Update EC table parameters
Changed Dead Time equation on page 9.
Copyright ©2012-2015, 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 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, 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
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17
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