L6482 step-clock mode

[PKrak.1]

Hello,

I am designing a stepper motor controller with L6482.

The choice of L6482 was made because of its integrated dual h-bridge gate drivers and relatively high voltage rating.

The chip features nice set of motion commands but due to specific demands I'm planning to use mainly step-clock mode. Unfortunately the Datasheet is not too detailed about step-clock mode. The questions are:

Can the chip in step-clock mode automaticaly switch between micro- and full-stepping when a speed treshold is reached?

Can it automaticaly reduce motor phases current when the motor is in standstill?

What is the function of "external switch input" in this mode?

And - out of curiosity - why STM decided not to implement "direction" pin for step-clock mode?

Best regards

Pawel.

[Cristiana SCARAMEL · Accepted solution]

Hello @PKEYrakowiak​ and welcome to the ST Community.

I report your questions with the relative answers:

Can the chip in step-clock mode automaticaly switch between micro- and full-stepping when a speed treshold is reached?

When the system is in Step-clock mode the device in not able to measure the STCK frequency and consequently SPEED register is set to zero and motor status is considered stopped. For the same reason the automatic switch to Full-step mode cannot work (SPEED should go over the threshold to switch to Full-step mode).

Can it automaticaly reduce motor phases current when the motor is in standstill?

This feature is not available. However, you can reduce target current through TVAL_HOLD register according to timings and values required by your application.

What is the function of "external switch input" in this mode?

The SW can be use to capture a switch turn-on event that is a SW falling edge (refer to L6482 datasheet Figure 13 at page 31). By default, a switch turn-on event causes a HardStop interrupt, otherwise the switch input events do not cause interrupts and the switch status information is at the user’s disposal.

Let me know if my reply fully answered your question, if so please "Select as Best" button.

[PKrak.1]

Thank you very much for clarification.

In that case I will have to live with micro-stepping in whole speed range. I expect that changing step resolution on the fly through SPI could be unreliable (if possible at all).

As to the holding current reduction I will probably design the circuit so it's possible to vary ADCIN voltage.

Regards

Pawel Krakowiak.

[Cristiana SCARAMEL]

Hi @PKEYrakowiak​,

as reported in the L6482 datasheet (section 6.4) the Step mode can only be changed when bridges are disabled.

Every time the step mode is changed, the electrical position (i.e. the point of microstepping sine wave that is generated) is reset to zero and the absolute position counter value (see Section 6.5) becomes meaningless. 

Have a nice day!