Allegro A4255CLN, A4255CA Datasheet
Data Sheet
MODE SELECT
MODE SELECT
STEP IN
RESET
GROUND
MONITOR OUT
SHIFT CLOCK
SERIAL DATA OUT
STROBE OUT
1
1
2
2
3
4
5
6
7
8
9
A4255CA
DD
18
MODE SELECT
DIRECTION
17
CONTROL IN
16
OSC/CLOCK IN
15
OSC/CLOCK OUT
14
SUPPLYV
13
PFD
12
PHASE
11
PFD
10
PHASE
A
A
B
B
Dwg. PP-071A
4255
MICROCONTROLLER
The A4255CA and A4255CLN microcontrollers make designing
with step motors easy, inexpensive, and productive. A reference design
technique is integral to the implementation of a system that includes the
power circuitry, a low-cost, 8-bit, preprogrammed microcontroller and
the other components needed to complete the control hardware. The
0
A4255Cx eliminates the need for software development, expedites the
product creation, and hastens the time to market.
The reference design can be utilized directly or integrated into a
larger printed wiring board. A further benefit is the compactness of the
circuit layout. Power-driver output ratings presently available with these
devices are 50 V and ±1.5 A (with the A3955 or A3957). A similar
device for 46 V and either 1.5 A (with the SLA7042M) or 3 A (with the
SLA7044M) is planned. The reference design supports stepping formats
that include full-step, half-step, quarter-step, eighth-step, and sixteenthstep (microstepping) increments for a two-phase stepping motor.
The A4255CA is furnished in an 18-pin dual in-line plastic package
for through-hole applications. The A4255CLN is furnished in a 20-lead
wide-body, shrink-pitch, small-outline plastic package (SSOP) with gullwing leads for minimum area, surface-mount applications.
26113
8-BIT
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VDD.......................... 7.0 V
Input Voltage Range,
VI........................ -0.3 V to VDD + 0.6 V
RESET Voltage, V
Input Clamp Current, IIK............... ±20 mA
Output Clamp Current, IOK............ ±20 mA
Operating Temperature Range,
TA.................................... 0°C to +70°C
Storage Temperature Range,
TS.............................. -55°C to +150°C
Caution: These CMOS devices have input
static protection (Class 3) but are still
susceptible to damage if exposed to extremely
high static electrical charges.
...................... 14 V
RESET
FEATURES
■ Full-, Half-, Quarter-, Eighth-, or Sixteenth-Step Increments
■ DC to 20 MHz Clock Input
■ Power-On Reset
■ Brown-Out Reset
■ High-Speed CMOS Technology
■ Low Power, <20 mA @ 5 V, 20 MHz
(Typically 9 mA)
Always order by complete part number:
Part Number Package
A4255CA 18-pin DIP
A4255CLN 20-lead shrink-pitch SOIC
4255
8-BIT
MICROCONTROLLER
A4255CLN
0.65 mm (0.026”) pitch
MODE SELECT
MODE SELECT
STEP IN
RESET
GROUND
GROUND
MONITOR OUT
SHIFT CLOCK
SERIAL DATA OUT
STROBE OUT
1
1
2
2
3
4
5
7
9
8
9
10
DD
DD
MODE SELECT
20
DIRECTION
19
CONTROL IN
18
OSC/CLOCK IN
17
OSC/CLOCK OUT
SUPPLYV
16
156
SUPPLYV
14
PFD
13
PHASE
PFD
12
PHASE
11
0
A
A
B
B
Dwg. PP-071-1
FUNCTIONAL DESCRIPTION
To ease and simplify the design effort, the user only
provides the following signals: (a) direction, (b) stepping
clock (8x the full-step frequency), (c) mode logic (three
inputs determine the operation for full, half, quarter, or
eighth stepping), (d) reset input (initiates a ‘detent’
position), and (e) recirculation control (this allows establishing the percent of fast- vs slow-decay in the phase
winding). The microcontroller program providess automatic recirculation control. This eliminates the need for
evaluating the impact of stepping rate vs the sinusoidal
current profile.
Although recirculation control can provide slight
improvements (i.e., lower current ripple, reduced motor
heating [a few degrees], and diminish audible noise levels
[minimal differences]), this entails an evaluation of the
motor (and step frequencies) to determine the proper ratio
of fast- and slow-decay. The benefits of tuning the
recirculation ratios are small, and the time and effort
required can be considerable. Hence, the uninitiated user
should opt for the automatic recirculation control, and
avoid the essentially unnecessary activity.
RECOMMENDED OPERATING CONDITIONS
over operating temperature range
Logic Supply Voltage Range, VDD............... 4.5 V to 5.5 V
High-Level Input Voltage, VIH............................ ≥ 0.85V
Low-level input voltage, VIL................................. ≤0.15V
MICROCONTROLLER OPERATION
Although ‘hardware’ control of the microstepping ICs
is feasible, without a specific (ASIC), monolithic IC
controller the prime solution becomes a ‘software’ option.
From the user’s perspective, a ‘preprogrammed’ microcontroller appears little, or no, different than a ‘dedicated’
controller and sequencer IC expressly created for microstepping applications of the power-driver ICs. Further,
the flexibility of a software-based drive is certainly a basic
benefit (high-volume production of 8-bit microcontrollers
transposes to low-cost circuitry).
As an indicator of the logic signals needed to control
the power ICs, Table 1 lists the required A3955 inputs to
the 3-bit DAC for eighth-step operation (the similar
A3957 uses a 4-bit DAC for sixteenth-step operation).
These I/O signals are serial data from the microcontroller,
then converted to a parallel mode by a 74HC595 as the
‘interface’ between the microcontroller and the two
microstepping power ICs.
The versatility offered by software control allows the
operating modes listed in Table 1. This table itemizes the
various logic inputs that determine direction, stepping
DD
DD
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 2000, Allegro MicroSystems, Inc.
FUNCTIONAL DESCRIPTION (cont’d)
format, reset, 1/8th vs 1/16th sub-steps, etc. Note that
during power up, shift clock (SCLK) is sampled for a pullup or pull-down resistor to establish the fractional step
limit. A pull up sets up a 1/8th-step format (for the
A3955) and pull down sets up 1/16th-operation (for the
A3957).
Table 2 lists the microcontroller terminal descriptions
and provides the essence of the circuit operation (a
schematic illustrating a typical stepper design follows). A
brief description of the microcontroller I/O should clarify
the connections of the various elements of the drive
electronics.
4255
8-BIT
MICROCONTROLLER
Table 1 — Controller/sequencer IC operational logic
Binary inputs Operating mode Comments
DIR MS2 MS1 MS0 (Command executed on L → H of CLK) (Applicable power ICs)
0000 CW, Full step (single-phase) A3955/57
0001 CW, Half step (constant torque) A3955/57
0010 CW, 1/4 step (constant torque) A3955/57
0011 CW, 1/8th step (constant torque) A3955/57
0100 CW, 1/16th step (constant torque) A3957 only
0101 Disable A3955/57 holding torque At present position
0110 Enable A3955/57 holding torque From present position
0111 Reset A4255 sequencer IC A3955/57
1000 CCW, full step (single-phase) A3955/57
1001 CCW, half step (constant torque) A3955/57
1010 CCW, 1/4 step (constant torque) A3955/57
1011 CCW, 1/8th step (constant torque) A3955/57
1100 CCW, 1/16th step (constant torque) A3957 only
1101 Disable A3955/57 holding torque At present position
1110 Enable A3955/57 holding torque From present position
1111 Reset A4255 sequencer IC A3955/57
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