UM1688 datasheet(37/41 Pages) STMICROELECTRONICS

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UM1688

Device configuration

3.2

Advanced current control (EVAL6472H/PD)

The following configuration gives good results with most of motors:



Minimum ON time = 4 µs.



Minimum OFF time = 21 µs.



Max. fast decay = 10 µs.



Max. fast decay at step change = 16 µs.



Target switching time = 48 µs.



Predictive current control enabled.

The impact of the timing parameters are explained in the application note “AN4158: Peak

current control with automatic decay adjustment and predictive current control: basics and

setup”.

The target phase current is set through the TVAL registers. The TVAL determinates the

current corresponding to the peak of the sine wave (microstepping operation).

3.3

Overcurrent and stall detection thresholds

The overcurrent protection and the stall detection (EVAL6470H\PD only) are implemented

measuring the current flowing into each integrated MOSFET.

The overcurrent protection threshold should be set just above the current rating of the

motor:

IOCDth > Imax,r.m.s. × √2

For example: if the maximum phase current of the motor is 2 Ar.m.s., the overcurrent

protection should be set to about 3 A.

Warning:

Important - it is strongly discouraged to disable the

overcurrent shutdown. It may result in critical failures.

The stall detection threshold should be just above the operating peak current of the

application. During the preliminary stages of evaluation, it can be set to the maximum value.

3.4

Speed profile

The max. speed parameter is the maximum speed the motor will run. By default, it is about

1000 step/s. That means, if you send a command to run at 2000 step/s, the motor speed is

limited at 1000 step/s.

This is an important safety feature in the final application, but not necessarily useful to

evaluate the device performances. Setting the parameter to high values (e.g. 6000 step/s)

allows evaluating the maximum speed which can be achieved by the application under test

through the speed tracking command (Run), but it probably limits the possibility to use

positioning commands (Move, GoTo, etc.).

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