4255 查看數據表（PDF） - Allegro MicroSystems

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4255

8-Bit microcontroller

Allegro MicroSystems 

4255

8-BIT

MICROCONTROLLER

A4255CLN

0.65 mm (0.026”) pitch

MODE SELECT1 1

MODE SELECT2 2

STEP IN 3

RESET 4

GROUND 5

GROUND 6

MONITOR OUT 79

SHIFT CLOCK 8

SERIAL DATA OUT 9

STROBE OUT 10

20 MODE SELECT0

DIRECTION

19 CONTROL IN

18 OSC/CLOCK IN

17 OSC/CLOCK OUT

VDD 16 SUPPLY

VDD 15 SUPPLY

14 PFDA

13 PHASEA

12 PFDB

11 PHASEB

Dwg. PP-071-1

RECOMMENDED OPERATING CONDITIONS

over operating temperature range

Logic Supply Voltage Range, VDD ............... 4.5 V to 5.5 V

High-Level Input Voltage, VIH ............................ ≥ 0.85VDD

Low-level input voltage, VIL ................................. ≤0.15VDD

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 estab-

lishing the percent of fast- vs slow-decay in the phase

winding). The microcontroller program providess auto-

matic 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.

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’ micro-

controller appears little, or no, different than a ‘dedicated’

controller and sequencer IC expressly created for mi-

crostepping 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

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

Copyright © 2000, Allegro MicroSystems, Inc.

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