ALLEGRO A3984

A3984
DMOS Microstepping Driver with Translator
Package LP
3
4
MS1
5
MS2
6
RESET
7
ROSC
8
SLEEP
9
23 ENABLE
22 OUT2B
21 VBB2
20 SENSE2
Translator
& Control Logic
VCP
VREG
24 GND
Charge
Pump
2
Reg
1
CP2
OSC
CP1
19 OUT2A
18 OUT1A
17 SENSE1
16 VBB1
VDD 10
15 OUT1B
STEP 11
14 DIR
REF 12
13 GND
Approximate Scale 1:1
ABSOLUTE MAXIMUM RATINGS
Load Supply Voltage,VBB ...................................35 V
Output Current, IOUT ......................................... ±2 A*
Logic Input Voltage, VIN ..................... –0.3 V to 7 V
Sense Voltage, VSENSE .......................................0.5 V
Reference Voltage, VREF ………..........................4 V
Operating Temperature Range
Ambient, TA ................................. –20°C to 85°C
Junction Temperature, TJ(MAX)..................... 150°C
Storage Temperature, TS .................... –55°C to 150°C
*Output current rating may be limited by duty cycle,
ambient temperature, and heat sinking. Under any
set of conditions, do not exceed the specified current
rating or a junction temperature of 150°C.
26184.30A
The A3984 is a complete microstepping motor driver with built-in
translator for easy operation. It is designed to operate bipolar stepper
motors in full-, half-, quarter-, and sixteenth-step modes, with an output
drive capacity of up to 35 V and ±2 A. The A3984 includes a fixed offtime current regulator which has the ability to operate in Slow or Mixed
decay modes.
The translator is the key to the easy implementation of the A3984.
Simply inputting one pulse on the STEP input drives the motor one
microstep. There are no phase sequence tables, high frequency control
lines, or complex interfaces to program. The A3984 interface is an ideal
fit for applications where a complex microprocessor is unavailable or is
overburdened.
The chopping control in the A3984 automatically selects the current
decay mode (Slow or Mixed). When a signal occurs at the STEP input
pin, the A3984 determines if that step results in a higher or lower
current in each of the motor phases. If the change is to a higher current,
then the decay mode is set to Slow decay. If the change is to a lower
current, then the current decay is set to Mixed (set initially to a fast
decay for a period amounting to 31.25% of the fixed off-time, then
to a slow decay for the remainder of the off-time). This current decay
control scheme results in reduced audible motor noise, increased step
accuracy, and reduced power dissipation.
Internal synchronous rectification control circuitry is provided to
improve power dissipation during PWM operation.
Internal circuit protection includes: thermal shutdown with hysteresis,
undervoltage lockout (UVLO), and crossover-current protection.
Special power-on sequencing is not required.
The A3984 is supplied in a low-profile (1.2 mm maximum), 24-pin
TSSOP with exposed thermal pad (package LP). It is also available
in a lead (Pb) free version (suffix –T), with 100% matte tin plated
leadframes.
FEATURES
Low RDS(ON) outputs
Automatic current decay mode detection/selection
Mixed and Slow current decay modes
Synchronous rectification for low power dissipation
Internal UVLO and thermal shutdown circuitry
Crossover-current protection
Use the following complete part number when ordering:
Part Number
Pb-free
A3984SLP
–
A3984SLP-T
Yes
Package
Description
24-pin, TSSOP
Exposed thermal pad
A3984
DMOS Microstepping Driver with Translator
Functional Block Diagram
0.1 uF
0.22 uF
VREG
VDD
Current
Regulator
ROSC
CP1
CP2
Charge
Pump
OSC
VCP
0.1 uF
REF
DMOS Full Bridge
DAC
VBB1
OUT1A
OUT1B
PWM Latch
Blanking
Mixed Decay
STEP
DIR
RESET
SENSE1
Gate
Drive
Translator
MS1
Control
Logic
MS2
DMOS Full Bridge
RS1
VBB2
OUT2A
OUT2B
PWM Latch
Blanking
Mixed Decay
ENABLE
SLEEP
SENSE2
RS2
DAC
VREF
2
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
ELECTRICAL CHARACTERISTICS1 at TA = 25°C, VBB = 35 V (unless otherwise noted)
Characteristics
Output Drivers
Min.
Typ.2
Max.
Units
8
0
3.0
–
–
–
–
–
–
–
–
–
–
–
–
–
0.350
0.300
–
–
–
–
–
–
–
–
35
35
5.5
0.450
0.370
1.2
1.2
4
2
10
8
5
10
V
V
V
Ω
Ω
V
V
mA
mA
μA
mA
mA
μA
VIN(1)
VDD×0.7
–
–
V
VIN(0)
–
–
V
–20
<1.0
VDD×0.3
20
μA
–20
<1.0
20
μA
50
300
1
30
30
–
0
–
–
–
475
–
500
1.3
40
37
4
3
±15
±5
±5
800
kΩ
mV
μs
μs
μs
V
μA
%
%
%
ns
165
15
2.7
0.10
–
–
3
–
°C
°C
V
V
Symbol
Load Supply Voltage Range
VBB
Logic Supply Voltage Range
VDD
Output On Resistance
RDSON
Body Diode Forward Voltage
VF
Motor Supply Current
IBB
Logic Supply Current
IDD
Test Conditions
Operating
During Sleep Mode
Operating
Source Driver, IOUT = –1.5 A
Sink Driver, IOUT = 1.5 A
Source Diode, IF = –1.5 A
Sink Diode, IF = 1.5 A
fPWM < 50 kHz
Operating, outputs disabled
Sleep Mode
fPWM < 50 kHz
Outputs off
Sleep Mode
Control Logic
Logic Input Voltage
Logic Input Current
Microstep Select 2
Input Hysteresis
Blank Time
IIN(1)
IIN(0)
VIN = VDD×0.7
VIN = VDD×0.3
MS2
VHYS(IN)
tBLANK
Current Trip-Level Error3
errI
Crossover Dead Time
Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
UVLO Enable Threshold
UVLO Hysteresis
tDT
–
150
0.7
20
23
0
–3
–
–
–
100
TJ
TJHYS
UVLO
UVHYS
–
–
2.35
0.05
Fixed Off-Time
tOFF
Reference Input Voltage Range
Reference Input Current
VREF
IREF
OSC > 3 V
ROSC = 25 kΩ
VREF = 2 V, %ITripMAX = 38.27%
VREF = 2 V, %ITripMAX = 70.71%
VREF = 2 V, %ITripMAX = 100.00%
VDD rising
1Negative current is defined as coming out of (sourcing from) the specified device pin.
2Typical data are for initial design estimations only, and assume optimum manufacturing and application conditions. Performance may vary for
individual units, within the specified maximum and minimum limits.
I = (ITrip – IProg ) ⁄ IProg , where IProg = %ITripMAX ITripMAX.
3err
×
3
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Test Conditions*
Value Units
One-layer PCB, one-sided with copper limited to solder pads
Package Thermal Resistance
RθJA
One layer PCB, two-sided with copper limited to solder pads and
3.8 in.2 of copper area on each side, connected to GND pins
High-K PCB (multilayer with significant copper areas, based on
JEDEC standard)
100
ºC/W
32
ºC/W
28
ºC/W
*In still air. Additional thermal information available on Allegro Web site.
Maximum Power Dissipation, PD(max)
5.5
5.0
4.5
Power Dissipation, PD (W)
4.0
H
(R igh
3.5
θJ
3.0
Lo
(R w-K
2.5
θJ
2.0
A
=
A
-K
= PC
28 B
ºC
/W
PC
32 B
ºC
/
)
W
)
Minim
u
m
(R
-K P
θJA =
100 CB
ºC/W
)
1.5
1.0
0.5
0.0
20
40
60
80
100
120
Temperature (°C)
140
160
180
4
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
tA
tB
STEP
tC
tD
MS1, MS2,
RESET, or DIR
Time Duration
Symbol
Typ.
Unit
STEP minimum, HIGH pulse width
tA
1
μs
STEP minimum, LOW pulse width
tB
1
μs
Setup time, input change to STEP
tC
200
ns
Hold time, input change to STEP
tD
200
ns
Figure 1. Logic Interface Timing Diagram
Table 1. Microstep Resolution Truth Table
MS1
MS2
Microstep Resolution
Excitation Mode
L
L
Full Step
2 Phase
H
L
Half Step
1-2 Phase
L
H
Quarter Step
W1-2 Phase
H
H
Sixteenth Step
4W1-2 Phase
5
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
Functional Description
Device Operation. The A3984 is a complete microstepping motor driver with a built-in translator for easy operation
with minimal control lines. It is designed to operate bipolar
stepper motors in full-, half-, quarter-, and sixteenth-step
modes. The currents in each of the two output full-bridges
and all of the N-channel DMOS FETs are regulated with
fixed off-time PMW (pulse width modulated) control circuitry. At each step, the current for each full-bridge is set by
the value of its external current-sense resistor (RS1 or RS2), a
reference voltage (VREF), and the output voltage of its DAC
(which in turn is controlled by the output of the translator).
At power-on or reset, the translator sets the DACs and the
phase current polarity to the initial Home state (shown in figures 2 through 5), and the current regulator to Mixed Decay
Mode for both phases. When a step command signal occurs
on the STEP input, the translator automatically sequences the
DACs to the next level and current polarity. (See table 2 for
the current-level sequence.) The microstep resolution is set
by the combined effect of inputs MS1 and MS2, as shown in
table 1.
When stepping, if the new output levels of the DACs are
lower than their previous output levels, then the decay mode
for the active full-bridge is set to Mixed. If the new output
levels of the DACs are higher than or equal to their previous
levels, then the decay mode for the active full-bridge is set
to Slow. This automatic current decay selection improves
microstepping performance by reducing the distortion of
the current waveform that results from the back EMF of the
motor.
RESET Input (RESET). The RESET input sets the
translator to a predefined Home state (shown in figures 2
through 5), and turns off all of the DMOS outputs. All STEP
inputs are ignored until the RESET input is set to high.
Step Input (STEP). A low-to-high transition on the STEP
input sequences the translator and advances the motor one
increment. The translator controls the input to the DACs and
the direction of current flow in each winding. The size of
the increment is determined by the combined state of inputs
MS1 and MS2.
Microstep Select (MS1 and MS2). Selects the microstepping format, as shown in table 1. MS2 has a 50 kΩ pulldown resistance. Any changes made to these inputs do not take
effect until the next STEP rising edge.
Direction Input (DIR). This determines the direction of
rotation of the motor. When low, the direction will be clockwise and when high, counterclockwise. Changes to this input
do not take effect until the next STEP rising edge.
Internal PWM Current Control. Each full-bridge is
controlled by a fixed off-time PWM current control circuit
that limits the load current to a desired value, ITRIP . Initially, a diagonal pair of source and sink DMOS outputs are
enabled and current flows through the motor winding and
the current sense resistor, RSx. When the voltage across RSx
equals the DAC output voltage, the current sense comparator resets the PWM latch. The latch then turns off either the
source DMOS FETs (when in Slow Decay Mode) or the sink
and source DMOS FETs (when in Mixed Decay Mode).
The maximum value of current limiting is set by the selection of RSx and the voltage at the VREF pin. The transconductance function is approximated by the maximum value of
current limiting, ITripMAX (A), which is set by
ITripMAX = VREF / ( 8
× RS )
where RS is the resistance of the sense resistor (Ω) and VREF
is the input voltage on the REF pin (V).
The DAC output reduces the VREF output to the current
sense comparator in precise steps, such that
Itrip = (%ITripMAX / 100)
× ITripMAX
(See table 2 for %ITripMAX at each step.)
It is critical that the maximum rating (0.5 V) on the SENSE1
and SENSE2 pins is not exceeded.
Fixed Off-Time. The internal PWM current control circuitry uses a one-shot circuit to control the duration of time
that the DMOS FETs remain off. The one shot off-time, tOFF,
is determined by the selection of an external resistor connected from the ROSC timing pin to ground. If the ROSC
6
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
pin is tied to an external voltage > 3 V, then tOFF defaults to
30 μs. The ROSC pin can be safely connected to the VDD
pin for this purpose. The value of tOFF (μs) is approximately
tOFF ≈ (ROSC ⁄ 880) + 1.6
Blanking. This function blanks the output of the current
sense comparators when the outputs are switched by the
internal current control circuitry. The comparator outputs are
blanked to prevent false overcurrent detection due to reverse
recovery currents of the clamp diodes, and switching transients related to the capacitance of the load. The blank time,
tBLANK (μs), is approximately
tBLANK ≈ 1 μs
Charge Pump (CP1 and CP2). The charge pump is
used to generate a gate supply greater than that of VBB
for driving the source-side DMOS gates. A 0.1 μF ceramic
capacitor, should be connected between CP1 and CP2. In
addition, a 0.1 μF ceramic capacitor is required between
VCP and VBB, to act as a reservoir for operating the
high-side DMOS gates.
VREG (VREG). This internally-generated voltage is used
to operate the sink-side DMOS outputs. The VREG pin must
be decoupled with a 0.22 μF capacitor to ground. VREG
is internally monitored. In the case of a fault condition, the
DMOS outputs of the A3984 are disabled.
Enable Input (ENABLE). This input turns on or off all of
the DMOS outputs. When set to a logic high, the outputs are
disabled. When set to a logic low, the internal control enables
the outputs as required. The translator inputs STEP, DIR,
MS1, and MS2, as well as the internal sequencing logic, all
remain active, independent of the ENABLE input state.
Shutdown. In the event of a fault, overtemperature
(excess TJ) or an undervoltage (on VCP), the DMOS outputs of the A3984 are disabled until the fault condition is
removed. At power-on, the UVLO (undervoltage lockout)
circuit disables the DMOS outputs and resets the translator to
the Home state.
Sleep Mode (SLEEP). To minimize power consumption
when the motor is not in use, this input disables much of the
internal circuitry including the output DMOS FETs, current
regulator, and charge pump. A logic low on the SLEEP pin
puts the A3984 into Sleep mode. A logic high allows normal
operation, as well as start-up (at which time the A3984 drives
the motor to the Home microstep position). When emerging
from Sleep mode, in order to allow the charge pump to stabilize, provide a delay of 1 ms before issuing a Step command.
Mixed Decay Operation. The bridge can operate in
Mixed Decay mode, depending on the step sequence, as
shown in figures 3 thru 5. As the trip point is reached, the
A3984 initially goes into a fast decay mode for 31.25% of
the off-time. tOFF. After that, it switches to Slow Decay mode
for the remainder of tOFF.
Synchronous Rectification. When a PWM-off cycle
is triggered by an internal fixed–off-time cycle, load current
recirculates according to the decay mode selected by the
control logic. This synchronous rectification feature turns on
the appropriate FETs during current decay, and effectively
shorts out the body diodes with the low DMOS RDSON. This
reduces power dissipation significantly, and can eliminate
the need for external Schottky diodes in many applications.
Turning off synchronous rectification prevents the reversal of
the load current when a zero-current level is detected.
7
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
STEP
STEP
100.00
100.00
70.71
70.71
Slow
100.00
–100.00
100.00
70.71
Phase 2
IOUT2B
Direction = H
(%)
0.00
Slow
Slow Slow
Mixed
Mixed
Mixed
Slow
Slow
Mixed
0.00
–70.71
–70.71
–100.00
–100.00
Figure 2. Decay Mode for Full-Step Increments
Mixed
0.00
–70.71
70.71
Phase 2
IOUT2A
Direction = H
(%)
Mixed
Slow
Home Microstep Position
–100.00
Home Microstep Position
–70.71
Slow
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
0.00
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
Slow
Figure 3. Decay Modes for Half-Step Increments
STEP
100.00
92.39
70.71
38.27
Slow
Mixed
Slow
Mixed
Slow
0.00
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
–38.27
–70.71
–92.39
–100.00
100.00
92.39
70.71
Phase 2
IOUT2B
Direction = H
(%)
38.27
Slow
Mixed
Slow
Mixed
Slow
Mixed
0.00
–38.27
–70.71
–92.39
–100.00
Figure 4. Decay Modes for Quarter-Step Increments
8
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
STEP
100.00
95.69
88.19
83.15
77.30
70.71
63.44
55.56
47.14
38.27
29.03
19.51
Phase 1
IOUT1A
Direction = H
(%)
9.8
Slow
0.00
Mixed
Slow
Mixed
–9.8
–19.51
–29.03
Home Microstep Position
–38.27
–47.14
–55.56
–63.44
–70.71
–77.30
–83.15
–88.19
–95.69
–100.00
100.00
95.69
88.19
83.15
77.30
70.71
63.44
55.56
47.14
38.27
29.03
19.51
Phase 2
IOUT2B
Direction = H
(%)
9.8
0.00
Slow
Mixed
Slow
Mixed
Slow
–9.8
–19.51
–29.03
–38.27
–47.14
–55.56
–63.44
–70.71
–77.30
–83.15
–88.19
–95.69
–100.00
Figure 5. Decay Modes for Sixteenth-Step Increments
9
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
Table 2. Step Sequencing Settings
Home microstep position at Step Angle 45º; DIR = H
Full
Step
#
Half
Step
#
1
1/4
Step
#
1
2
1
2
3
4
3
5
6
2
4
7
8
1/16
Step
#
1
Phase 1
Current
Phase 2
Current
[% ItripMax]
[% ItripMax]
(%)
100.00
(%)
0.00
Step
Angle
(º)
0.0
Full
Step
#
Half
Step
#
5
1/4
Step
#
9
1/16
Step
#
33
Phase 1
Current
Phase 2
Current
[% ItripMax]
[% ItripMax]
Step
Angle
(%)
0.00
180.0
(%)
–100.00
(º)
2
99.52
9.80
5.6
34
–99.52
–9.80
185.6
3
98.08
19.51
11.3
35
–98.08
–19.51
191.3
4
95.69
29.03
16.9
36
–95.69
–29.03
196.9
5
92.39
38.27
22.5
37
–92.39
–38.27
202.5
6
88.19
47.14
28.1
38
–88.19
–47.14
208.1
7
83.15
55.56
33.8
39
–83.15
–55.56
213.8
8
77.30
63.44
39.4
40
–77.30
–63.44
219.4
9
70.71
70.71
45.0
41
–70.71
–70.71
225.0
10
63.44
77.30
50.6
42
–63.44
–77.30
230.6
11
55.56
83.15
56.3
43
–55.56
–83.15
236.3
12
47.14
88.19
61.9
44
–47.14
–88.19
241.9
13
38.27
92.39
67.5
45
–38.27
–92.39
247.5
14
29.03
95.69
73.1
46
–29.03
–95.69
253.1
15
19.51
98.08
78.8
47
–19.51
–98.08
258.8
16
9.80
99.52
84.4
48
–9.80
–99.52
264.4
17
0.00
100.00
90.0
49
0.00
–100.00
270.0
10
3
6
11
12
7
13
18
–9.80
99.52
95.6
50
9.80
–99.52
275.6
19
–19.51
98.08
101.3
51
19.51
–98.08
281.3
20
–29.03
95.69
106.9
52
29.03
–95.69
286.9
21
–38.27
92.39
112.5
53
38.27
–92.39
292.5
22
–47.14
88.19
118.1
54
47.14
–88.19
298.1
23
–55.56
83.15
123.8
55
55.56
–83.15
303.8
24
–63.44
77.30
129.4
56
63.44
–77.30
309.4
25
–70.71
70.71
135.0
57
70.71
–70.71
315.0
26
–77.30
63.44
140.6
58
77.30
–63.44
320.6
27
–83.15
55.56
146.3
59
83.15
–55.56
326.3
28
–88.19
47.14
151.9
60
88.19
–47.14
331.9
29
–92.39
38.27
157.5
61
92.39
–38.27
337.5
30
–95.69
29.03
163.1
62
95.69
–29.03
343.1
31
–98.08
19.51
168.8
63
98.08
–19.51
348.8
32
–99.52
9.80
174.4
64
99.52
–9.80
354.4
14
4
8
15
16
10
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
Pin List Table
Name
Description
Number
CP1
Charge pump capacitor 1
1
CP2
Charge pump capacitor 2
2
VCP
Reservoir capacitor
3
Regulator decoupling
4
MS1
Logic input
5
MS2
Logic input
6
RESET
Logic input
7
ROSC
Timing set
8
SLEEP
Logic input
9
VDD
Logic supply
10
STEP
Logic input
11
REF
Current trip reference voltage input
12
GND
Ground*
13
DIR
Logic input
14
DMOS Full Bridge 1 Output B
15
Load supply
16
Sense resistor for Bridge 1
17
OUT1A
DMOS Full Bridge 1 Output A
18
OUT2A
DMOS Full Bridge 2 Output A
19
Sense resistor for Bridge 2
20
Load supply
21
DMOS Full Bridge 2 Output B
22
Logic input
23
Ground*
24
VREG
OUT1B
VBB1
SENSE1
SENSE2
VBB2
OUT2B
ENABLE
GND
*The two GND pins must be tied together externally by connecting
to the exposed pad ground plane under the device.
11
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
LP Package, 24-Pin TSSOP with Exposed Thermal Pad
12
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
A3984
DMOS Microstepping Driver with Translator
The products described here are manufactured under one or
more U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. 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 products are not authorized for use as critical components in life-support devices or systems without express written
approval.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other
rights of third parties which may result from its use.
Copyright©2005 AllegroMicrosystems, Inc.
13
26184.30A
Allegro MicroSystems, Inc.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com