A4988 Datasheet

A4988
DMOS Microstepping Driver with Translator
and Overcurrent Protection
Features and Benefits
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
Low Rds(on) outputs
Automatic current decay mode detection/selection
Mixed and slow current decay modes
Synchronous rectification for low power dissipation
Internal UVLO
Crossover-current protection
3.3 and 5 V compatible logic supply
Thermal shutdown circuitry
Short-to-ground protection
Shorted load protection
Five selectable step modes: full, 1/2, 1/4, 1/8, and 1/16
Package:
28-contact QFN
Description
The A4988 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-, eighth-, and
sixteenth-step modes, with an output drive capacity of up to 35 V and ±2 A. The A4988 includes a fixed off-time 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
A4988. 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 A4988 interface is an ideal fit for applications where a
complex microprocessor is unavailable or is overburdened.
During stepping operation, the chopping control in the A4988
automatically selects the current decay mode: slow or mixed. In
mixed decay mode, the device is set initially to a fast decay for
a proportion of the fixed off-time, then to a slow decay for the
remainder of the off-time. Mixed decay current control results
in reduced audible motor noise, increased step accuracy, and
reduced power dissipation.
with exposed thermal pad
5 mm × 5 mm × 0.90 mm
(ET package)
Not to scale
Continued on the next page…
Typical Application Diagram
VDD
0.1 µF
VREG ROSC
0.22 µF
0.1 µF
0.22 µF
CP1
CP2
VCP
VDD
VBB2
5 kΩ
Microcontroller or
Controller Logic
SLEEP
STEP
VBB1
OUT1A
A4988
OUT1B
SENSE1
MS1
MS2
MS3
OUT2A
DIR
OUT2B
ENABLE
SENSE2
RESET
VREF
4988-DS, Rev. 6
GND
GND
100 µF
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Description (continued)
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 A4988 is supplied in a surface-mount QFN package (ET), 5 mm
× 5 mm, with a nominal overall package height of 0.90 mm and an
exposed pad for enhanced thermal dissipation. It is lead (Pb) free
(suffix –T), with 100% matte-tin-plated leadframes.
Selection Guide
Part Number
A4988SETTR-T
Package
Packing
28-contact QFN with exposed thermal pad
1500 pieces per 7-in. reel
Absolute Maximum Ratings
Characteristic
Symbol
Load Supply Voltage
VBB
Notes
Rating
Units
35
V
Output Current
IOUT
±2
A
Logic Input Voltage
VIN
–0.3 to 5.5
V
Logic Supply Voltage
VDD
–0.3 to 5.5
V
–2.0 to 37
V
VSENSE
–0.5 to 0.5
V
VREF
5.5
V
–20 to 85
ºC
TJ(max)
150
ºC
Tstg
–55 to 150
ºC
Motor Outputs Voltage
Sense Voltage
Reference Voltage
Operating Ambient Temperature
Maximum Junction
Storage Temperature
TA
Range S
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Functional Block Diagram
0.1 µF
0.22 µF
VREG
VDD
Current
Regulator
ROSC
CP1
CP2
Charge
Pump
OSC
VCP
0.1 µF
DMOS Full Bridge
REF
DAC
VBB1
OUT1A
OUT1B
PWM Latch
Blanking
Mixed Decay
STEP
OCP
Gate
Drive
DIR
RESET
MS1
Translator
Control
Logic
MS2
PWM Latch
Blanking
Mixed Decay
ENABLE
SLEEP
DAC
DMOS Full Bridge
VBB2
RS1
OUT2A
OCP
MS3
SENSE1
OUT2B
SENSE2
RS2
VREF
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4988
DMOS Microstepping Driver with Translator
and Overcurrent Protection
ELECTRICAL CHARACTERISTICS1 at TA = 25°C, VBB = 35 V (unless otherwise noted)
Characteristics
Output Drivers
Symbol
Load Supply Voltage Range
VBB
Logic Supply Voltage Range
VDD
Output On-Resistance
Rds(on)
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
Min.
Typ.2
Max.
Units
8
0
3
–
–
–
–
–
–
–
–
–
–
–
–
–
320
320
–
–
–
–
–
–
–
–
35
35
5.5
430
430
1.2
1.2
4
2
10
8
5
10
V
V
V
mΩ
mΩ
V
V
mA
mA
µA
mA
mA
µA
VDD × 0.7
–
–20
–20
–
–
–
5
0.7
20
23
0
–3
–
–
–
100
–
–
<1.0
<1.0
100
50
100
11
1
30
30
–
0
–
–
–
475
–
VDD × 0.3
20
20
–
–
–
19
1.3
40
37
4
3
±15
±5
±5
800
V
V
µA
µA
kΩ
kΩ
kΩ
%
μs
μs
μs
V
μA
%
%
%
ns
2.1
–
–
2.7
–
–
165
15
2.8
90
–
–
–
2.9
–
A
°C
°C
V
mV
Control Logic
Logic Input Voltage
Logic Input Current
Microstep Select
Logic Input Hysteresis
Blank Time
VIN(1)
VIN(0)
IIN(1)
IIN(0)
RMS1
RMS2
RMS3
VHYS(IN)
tBLANK
Fixed Off-Time
tOFF
Reference Input Voltage Range
Reference Input Current
VREF
IREF
Current Trip-Level Error3
errI
Crossover Dead Time
Protection
Overcurrent Protection Threshold4
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
VDD Undervoltage Lockout
VDD Undervoltage Hysteresis
tDT
IOCPST
TTSD
TTSDHYS
VDDUVLO
VDDUVLOHYS
VIN = VDD × 0.7
VIN = VDD × 0.3
MS1 pin
MS2 pin
MS3 pin
As a % of VDD
OSC = VDD or GND
ROSC = 25 kΩ
VREF = 2 V, %ITripMAX = 38.27%
VREF = 2 V, %ITripMAX = 70.71%
VREF = 2 V, %ITripMAX = 100.00%
VDD rising
1 For
input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
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.
3V
ERR = [(VREF/8) – VSENSE] / (VREF/8).
4 Overcurrent protection (OCP) is tested at T = 25°C in a restricted range and guaranteed by characterization.
A
2 Typical
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
THERMAL CHARACTERISTICS
Characteristic
Symbol
Package Thermal Resistance
RθJA
Test Conditions*
Value Units
Four-layer PCB, based on JEDEC standard
32
ºC/W
*Additional thermal information available on Allegro website.
Power Dissipation versus Ambient Temperature
4.00
Power Dissipation, PD (W)
3.50
3.00
2.50
R
θJ
2.00
A
=
32
ºC
/W
1.50
1.00
0.50
0
20
40
60
80
100
120
Temperature, TA (°C)
140
160
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
tA
tB
STEP
tC
tD
MS1, MS2, MS3,
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: Microstepping Resolution Truth Table
MS1
MS2
MS3
Microstep Resolution
Excitation Mode
L
L
L
Full Step
2 Phase
H
L
L
Half Step
1-2 Phase
L
H
L
Quarter Step
W1-2 Phase
H
H
L
Eighth Step
2W1-2 Phase
H
H
H
Sixteenth Step
4W1-2 Phase
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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6
A4988
DMOS Microstepping Driver with Translator
and Overcurrent Protection
Functional Description
Device Operation. The A4988 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-, eighth, 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 PWM
(pulse-width modulated) control circuitry. At each step, the current for each full-bridge is set by the value of its external currentsense resistor (RS1 and 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 9
through 13), 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 the MSx inputs, 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.
Mixed Decay Operation. The bridge operates in Mixed
decay mode, at power-on and reset, and during normal running
according to the ROSC configuration and the step sequence, as
shown in Figures 9 through 13. During Mixed decay mode, when
the trip point is reached, the A4988 initially goes into a fast decay
interval for 31.25% of the off-time, tOFF . After that, it switches
to slow decay for the remainder of tOFF. A timing diagram for this
feature appears on the next page.
Typically, mixed decay is only necessary when the current in the
winding is going from a higher value to a lower value as determined
by the state of the translator. For most loads, automatically selected
mixed decay is convenient because it minimizes ripple when the
current is rising and prevents missed steps when the current is falling.
For some applications where microstepping at very low speeds is
necessary, the lack of back EMF in the winding causes the current to
increase in the load quickly, resulting in missed steps. This is shown
in Figure 2. By pulling the ROSC pin to ground, mixed decay is set
to be active 100% of the time, for both rising and falling currents, and
prevents missed steps as shown in Figure 3. If this is not an issue, it
is recommended that automatically selected mixed decay be used,
because it will produce reduced ripple currents. Refer to the Fixed
Off-Time section for details.
Low Current Microstepping. Intended for applications
where the minimum on-time prevents the output current from
regulating to the programmed current level at low current steps.
To prevent this, the device can be set to operate in Mixed decay
mode on both rising and falling portions of the current waveform.
This feature is implemented by shorting the ROSC pin to ground.
Microstep Select (MSx). The microstep resolution is set by
the voltage on logic inputs MSx, as shown in Table 1. The MS1 and In this state, the off-time is internally set to 30 µs.
MS3 pins have a 100 kΩ pull-down resistance, and the MS2 pin
has a 50 kΩ pull-down resistance. When changing the step mode,
Reset Input ( R̄¯ Ē¯ S̄¯ Ē¯ T̄¯ ). The R̄¯ Ē ¯S̄¯ Ē¯ T̄¯ input sets the translator
the change does not take effect until the next STEP rising edge.
to a predefined Home state (shown in Figures 9 through 13), and
turns off all of the FET outputs. All STEP inputs are ignored until
If the step mode is changed without a translator reset, and abso¯ input is set to high.
the R̄¯ Ē¯ S̄¯ Ē¯ T̄
lute position must be maintained, it is important to change the
step mode at a step position that is common to both step modes in
Step Input (STEP). A low-to-high transition on the STEP
order to avoid missing steps. When the device is powered down,
or reset due to TSD or an overcurrent event, the translator is set to input sequences the translator and advances the motor one increthe home position which is by default common to all step modes. ment. The translator controls the input to the DACs and the direc-
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115 Northeast Cutoff
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7
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Slow
Decay
Mixed
Decay
Slow
Decay
Mixed
Decay
Slow
Decay
Mixed
Decay
Slow
Decay
Mixed
Decay
Missed
Step
Voltage on ROSC terminal 2 V/div.
Step input 10 V/div.
t → , 1 s/div.
Figure 2: Missed Steps in Low-Speed Microstepping
Mixed Decay
ILOAD 500 mA/div.
Step input 10 V/div.
No Missed
Steps
t → , 1 s/div.
Figure 3: Continuous Stepping Using Automatically-Selected Mixed Stepping (ROSC pin grounded)
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115 Northeast Cutoff
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8
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
tion of current flow in each winding. The size of the increment is
determined by the combined state of the MSx inputs.
Direction Input (DIR). This determines the direction of rotation of the motor. Changes to this input do not take effect until the
next STEP rising edge.
Internal PWM Current Control. Each full-bridge is con-
trolled 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 FET 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 the appropriate source driver and initiates a fixed offtime 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
× RS)
ITripMAX = VREF / ( 8 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 off-time, tOFF, is determined by the
ROSC terminal. The ROSC terminal has three settings:
▪ ROSC tied to VDD — off-time internally set to 30 µs; decay
mode is automatic Mixed, except when in full-step where
decay mode is set to Slow.
▪ ROSC tied directly to ground — off-time internally set to
30 µs; current decay is set to Mixed for both increasing and
decreasing currents for all step modes.
▪ ROSC through a resistor to ground — off-time is determined
by the following formula; the decay mode is automatic Mixed
for all step modes except full-step which is set to Slow.
tOFF ≈ ROSC ⁄ 825
where tOFF is in µs.
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
Shorted Load and Short-to-Ground Protection.
If the motor leads are shorted together, or if one of the leads is
shorted to ground, the driver will protect itself by sensing the
overcurrent event and disabling the driver that is shorted, protecting the device from damage. In the case of a short-to-ground, the
¯ input goes
device will remain disabled (latched) until the S̄ L̄¯ Ē¯ Ē¯ P̄
high or VDD power is removed. A short-to-ground overcurrent
event is shown in Figure 4.
When the two outputs are shorted together, the current path is
through the sense resistor. After the blanking time (≈1 µs) expires,
the sense resistor voltage is exceeding its trip value, due to the
overcurrent condition that exists. This causes the driver to go into
a fixed off-time cycle. After the fixed off-time expires, the driver
turns on again and the process repeats. In this condition, the
driver is completely protected against overcurrent events, but the
short is repetitive with a period equal to the fixed off-time of the
driver. This condition is shown in Figure 5.
During a shorted load event, it is normal to observe both a positive and negative current spike as shown in Figure 3, due to the
direction change implemented by the Mixed decay feature. This is
shown in Figure 6. In both instances, the overcurrent circuitry is
protecting the driver and prevents damage to the device.
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 FET 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 FET gates.
Capacitor values should be Class 2 dielectric ±15% maximum,
or tolerance R, according to EIA (Electronic Industries Alliance)
specifications.
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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9
A4988
DMOS Microstepping Driver with Translator
and Overcurrent Protection
VREG (VREG). This internally generated voltage is used to
operate the sink-side FET outputs. The nominal output voltage
of the VREG terminal is 7 V. The VREG pin must be decoupled
with a 0.22 µF ceramic capacitor to ground. VREG is internally
monitored. In the case of a fault condition, the FET outputs of the
A4988 are disabled.
5 A / div.
Fault
latched
Capacitor values should be Class 2 dielectric ±15% maximum,
or tolerance R, according to EIA (Electronic Industries Alliance)
specifications.
Enable Input ( Ē¯ N̄¯ Ā¯ B̄¯ L̄¯ Ē¯ ). This input turns on or off all of the
FET 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, and MSx, as well as
the internal sequencing logic, all remain active, independent of the
¯
Ē¯ N̄¯ Ā¯ B̄
¯L̄
Ē¯ input state.
Shutdown. In the event of a fault, overtemperature (excess TJ)
or an undervoltage (on VCP), the FET outputs of the A4988 are
disabled until the fault condition is removed. At power-on, the
UVLO (undervoltage lockout) circuit disables the FET outputs
and resets the translator to the Home state.
t→
Figure 4: Short-to-Ground Event
5 A / div.
Fixed off-time
Sleep Mode ( S̄¯ L̄¯ Ē¯ Ē¯ P̄¯ ). To minimize power consumption
when the motor is not in use, this input disables much of the
internal circuitry including the output FETs, current regulator,
and charge pump. A logic low on the S̄ L̄
¯Ē¯ Ē¯ P̄¯ pin puts the A4988
into Sleep mode. A logic high allows normal operation, as well
as startup (at which time the A4988 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 operates in Mixed
decay mode, depending on the step sequence, as shown in Figures 9 through 13. As the trip point is reached, the A4988 initially
goes into a fast decay interval for 31.25% of the off-time, tOFF.
After that, it switches to slow decay for the remainder of tOFF. A
timing diagram for this feature appears in Figure 7.
t→
Figure 5. Shorted Load (OUTxA → OUTxB) in Slow Decay Mode
5 A / div.
Fixed off-time
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 FET Rds(on). This reduces power dissipation
significantly, and can eliminate the need for external Schottky
diodes in many applications. Synchronous rectification turns off
when the load current approaches zero (0 A), preventing reversal
of the load current.
Fast decay portion
(direction change)
t→
Figure 6: Shorted Load (OUTxA → OUTxB) in Mixed Decay Mode
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10
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
VSTEP
100.00
70.71
See Enlargement A
IOUT
0
–70.71
–100.00
Enlargement A
toff
IPEAK
tFD
tSD
Slow Decay
Mixed Decay
IOUT
Fa
st
De
ca
y
t
Symbol
toff
IPEAK
Characteristic
Device fixed off-time
Maximum output current
tSD
Slow decay interval
tFD
Fast decay interval
IOUT
Device output current
Figure 7: Current Decay Modes Timing Chart
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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11
A4988
DMOS Microstepping Driver with Translator
and Overcurrent Protection
Application Layout
Layout. The printed circuit board should use a heavy groundplane. For optimum electrical and thermal performance, the
A4988 must be soldered directly onto the board. Pins 3 and 18
are internally fused, which provides a path for enhanced thermal
dissipation. Theses pins should be soldered directly to an exposed
surface on the PCB that connects to thermal vias are used to
transfer heat to other layers of the PCB.
In order to minimize the effects of ground bounce and offset
issues, it is important to have a low-impedance single-point
ground, known as a star ground, located very close to the device.
By making the connection between the pad and the ground plane
directly under the A4988, that area becomes an ideal location for
a star ground point. A low-impedance ground will prevent ground
bounce during high-current operation and ensure that the supply
voltage remains stable at the input terminal.
The two input capacitors should be placed in parallel, and as
close to the device supply pins as possible. The ceramic capacitor (CIN1) should be closer to the pins than the bulk capacitor
(CIN2). This is necessary because the ceramic capacitor will be
responsible for delivering the high-frequency current components.
The sense resistors, RSx , should have a very low-impedance
path to ground, because they must carry a large current while
supporting very accurate voltage measurements by the current
sense comparators. Long ground traces will cause additional
voltage drops, adversely affecting the ability of the comparators
to accurately measure the current in the windings. The SENSEx
pins have very short traces to the RSx resistors and very thick,
low-impedance traces directly to the star ground under the
device. If possible, there should be no other components on the
sense circuits.
Solder
A4988
Trace (2 oz.)
Signal (1 oz.)
Ground (1 oz.)
PCB
Thermal (2 oz.)
Thermal Vias
RS1
RS2
ENABLE
VBB1
SENSE1
NC
OUT1A
NC
PAD
DIR
VDD
C6
SLEEP
STEP
NC
ROSC
VCP
RESET
GND
REF
MS3
CP2
VREG
C4
A4988
GND
CP1
MS1
C3
VBB
C2
OUT1B
OUT2B
MS2
1
OUT2A
VBB2
C9
SENSE2
C7
R3
R2
VDD
C1
C8
R6
R1
Figure 8: Typical Application and Circuit Layout
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Worcester, Massachusetts 01615-0036 U.S.A.
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12
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Pin Circuit Diagrams
VDD
VBB
VBB
8V
GND
GND
SENSE
GND
CP2
GND
GND
GND
GND
GND
VBB
10 V
CP1
40 V
PGND
VREG
VCP
VREG
DMOS
Parasitic
GND
8V
MS1
MS2
MS3
DIR
VREF
ROSC
SLEEP
VBB
OUT
DMOS
Parasitic
8V
GND
GND
DMOS
Parasitic
GND
Allegro MicroSystems, LLC
115 Northeast Cutoff
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13
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
RESET
STEP
STEP
100.00
Slow
70.71
–70.71
–100.00
100.00
Home Microstep Position
0.00
Phase 2
IOUT2A
Direction = H
(%)
–100.00
100.00
70.71
Phase 2
IOUT2B
Direction = H
(%)
0.00
–70.71
Slow
Mixed
Mixed
0.00
–70.71
70.71
Slow
Mixed
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
Slow
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
Mixed*
70.71
Mixed*
Mixed*
Slow Slow
Mixed
Home Microstep Position
100.00
Slow
Mixed
Slow
Mixed
0.00
–70.71
–100.00
–100.00
*With ROSC pin tied to GND
*With ROSC pin tied to GND
DIR= H
DIR= H
Figure 9: Decay Mode for Full-Step Increments
Figure 10: Decay Modes for Half-Step Increments
STEP
100.00
92.39
70.71
Slow
Mixed
Slow
–38.27
–70.71
–92.39
–100.00
100.00
92.39
Slow
Mixed*
70.71
Phase 2
IOUT2B
Direction = H
(%)
Mixed
0.00
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
Mixed*
38.27
38.27
Slow
Mixed
Slow
Mixed
Slow
Mixed
0.00
–38.27
–70.71
–92.39
–100.00
*With ROSC pin tied to GND
DIR= H
Figure 11: Decay Modes for Quarter-Step Increments
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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14
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
STEP
100.00
92.39
83.15
70.71
55.56
Mixed*
38.27
19.51
0.00
Slow
–19.51
–38.27
–55.56
–70.71
–83.15
–92.39
–100.00
100.00
92.39
83.15
70.71
55.56
Phase 2
IOUT2B
Direction = H
(%)
Mixed
0.00
Mixed
Mixed
Slow
Mixed*
38.27
19.51
Slow
Home Microstep Position
Phase 1
IOUT1A
Direction = H
(%)
Mixed
Slow
–19.51
–38.27
–55.56
–70.71
–83.15
–92.39
–100.00
*With ROSC pin tied to GND
DIR= H
Figure 12: Decay Modes for Eighth-Step Increments
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
STEP
100.00
95.69
88.19
83.15
77.30
70.71
63.44
55.56
47.14
Mixed*
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
Mixed*
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
*With ROSC pin tied to GND
DIR= H
Figure 13: Decay Modes for Sixteenth-Step Increments
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
16
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Table 2: Step Sequencing Settings
Home microstep position at Step Angle 45º; DIR = H
Full
Step
#
Half
Step
#
1
1/4
Step
#
1
1/8
Step
#
1
2
2
3
4
1
2
3
5
6
4
7
8
3
5
9
10
6
11
12
2
4
7
13
14
8
15
16
1/16
Step
#
1
Phase 1
Current
[% ItripMax]
(%)
100.00
Phase 2
Current
[% ItripMax]
(%)
0.00
Step
Angle
(º)
0.0
2
99.52
9.80
5.6
3
98.08
19.51
11.3
4
95.69
29.03
16.9
5
92.39
38.27
22.5
6
88.19
47.14
28.1
7
83.15
55.56
33.8
8
77.30
63.44
39.4
9
70.71
70.71
45.0
10
63.44
77.30
50.6
11
55.56
83.15
56.3
12
47.14
88.19
61.9
13
38.27
92.39
67.5
14
29.03
95.69
73.1
15
19.51
98.08
78.8
16
9.80
99.52
84.4
17
0.00
100.00
90.0
18
–9.80
99.52
95.6
19
–19.51
98.08
101.3
20
–29.03
95.69
106.9
21
–38.27
92.39
112.5
22
–47.14
88.19
118.1
23
–55.56
83.15
123.8
24
–63.44
77.30
129.4
25
–70.71
70.71
135.0
26
–77.30
63.44
140.6
27
–83.15
55.56
146.3
28
–88.19
47.14
151.9
29
–92.39
38.27
157.5
30
–95.69
29.03
163.1
31
–98.08
19.51
168.8
32
–99.52
9.80
174.4
Full
Step
#
Half
Step
#
5
1/4
Step
#
9
1/8
Step
#
17
18
10
19
20
3
6
11
21
22
12
23
24
7
13
25
26
14
27
28
4
8
15
29
30
16
31
32
Phase 1
Current
Phase 2
Current
1/16
Step
#
33
[% ItripMax]
34
–99.52
–9.80
185.6
35
–98.08
–19.51
191.3
36
–95.69
–29.03
196.9
37
–92.39
–38.27
202.5
38
–88.19
–47.14
208.1
39
–83.15
–55.56
213.8
40
–77.30
–63.44
219.4
41
–70.71
–70.71
225.0
42
–63.44
–77.30
230.6
43
–55.56
–83.15
236.3
44
–47.14
–88.19
241.9
45
–38.27
–92.39
247.5
46
–29.03
–95.69
253.1
47
–19.51
–98.08
258.8
48
–9.80
–99.52
264.4
49
0.00
–100.00
270.0
50
9.80
–99.52
275.6
51
19.51
–98.08
281.3
52
29.03
–95.69
286.9
53
38.27
–92.39
292.5
54
47.14
–88.19
298.1
55
55.56
–83.15
303.8
56
63.44
–77.30
309.4
57
70.71
–70.71
315.0
58
77.30
–63.44
320.6
59
83.15
–55.56
326.3
60
88.19
–47.14
331.9
61
92.39
–38.27
337.5
62
95.69
–29.03
343.1
63
98.08
–19.51
348.8
64
99.52
–9.80
354.4
(%)
–100.00
[% ItripMax]
(%)
0.00
Step
Angle
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
(º)
180.0
17
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
22 VBB1
23 SENSE1
24 OUT1A
25 NC
26 OUT2A
27 SENSE2
28 VBB2
Pinout Diagram
OUT2B
1
21 OUT1B
ENABLE
2
20 NC
GND
3
CP1
4
CP2
5
17 REF
VCP
6
16 STEP
NC
7
15 VDD
SLEEP 14
ROSC 13
18 GND
RESET 12
MS3 11
9
MS1
MS2 10
8
VREG
Terminal List Table
19 DIR
PAD
Name
Number
Description
CP1
4
Charge pump capacitor terminal
CP2
5
Charge pump capacitor terminal
VCP
6
Reservoir capacitor terminal
VREG
8
Regulator decoupling terminal
MS1
9
Logic input
MS2
10
Logic input
MS3
11
Logic input
R̄¯ Ē¯ S̄¯ Ē¯ T̄¯
12
Logic input
ROSC
13
Timing set
S̄¯ L̄¯ Ē¯ Ē¯ P̄¯ 14
Logic input
VDD
15
Logic supply
STEP
16
Logic input
REF
17
Gm reference voltage input
GND
3, 18
Ground*
DIR
19
Logic input
OUT1B
21
DMOS Full Bridge 1 Output B
VBB1
22
Load supply
SENSE1
23
Sense resistor terminal for Bridge 1
OUT1A
24
DMOS Full Bridge 1 Output A
OUT2A
26
DMOS Full Bridge 2 Output A
SENSE2
27
Sense resistor terminal for Bridge 2
VBB2
28
Load supply
OUT2B
1
DMOS Full Bridge 2 Output B
Ē¯ N̄¯ Ā¯ B̄¯ L̄¯ Ē¯
2
Logic input
NC
7, 20, 25
PAD
–
No connection
Exposed pad for enhanced thermal dissipation*
*The GND pins must be tied together externally by connecting to the PAD ground plane
under the device.
Allegro MicroSystems, LLC
115 Northeast Cutoff
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1.508.853.5000; www.allegromicro.com
18
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
ET Package, 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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115 Northeast Cutoff
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1.508.853.5000; www.allegromicro.com
19
DMOS Microstepping Driver with Translator
and Overcurrent Protection
A4988
Revision History
Revision
Revision Date
4
January 27, 2012
5
May 7, 2014
6
January 14, 2016
Description of Revision
Updated IOCPST
Revised text on page 9; revised Figure 8 and Table 2
Updated VBB, IBB, and IDD in Electrical Characteristics table
Copyright ©2016, 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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20
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