UM1691 datasheet(14/41 Pages) STMICROELECTRONICS

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General description

UM1691

14/41

DocID025486 Rev 2

4.2.2

Voltage mode driving

The configuration parameters of the voltage mode driving can be obtained through the

BEMF compensation tool embedded into the SPINFamily software.

A wrong setup of these parameters could cause several issues, in particular:



The phase current decreases with the speed and the motor will stall.



The wrong voltage is applied to the motor and the system is very noisy.



The phase current reaches the overcurrent limit.

The BEMF compensation form uses the application parameters as inputs in order to

evaluate the proper device setup.

The required inputs are:



Supply voltage.



Target phase current (r.m.s. value) at different motion conditions (acceleration,

deceleration, constant speed and holding).



Target operating speed (maximum speed).



Motor characteristics.

The motor characteristics are: electrical constant (Ke), phase inductance and resistance.

The inductance and the resistance of the phase are given in the motor datasheet. The Ke is

rarely given in the specification and must be measured.

In the help section of the SPINFamily software a step by step procedure is explained. The

same procedure can also be found in the application note “AN4144: Voltage mode control

operation and parameter optimization” on www.st.com.

Click on the “evaluate” button to get the suggested setup for the voltage mode driving. Then

click on “write” button to copy the data in the registers of the device.

4.2.3

Overcurrent and stall detection thresholds

The overcurrent protection and the stall detection 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.

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