DocID025458 Rev 2

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UM1685

Device configuration

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3.2

Advanced current control (EVAL6482H)

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” on www.st.com.

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

reference voltage (i.e. the voltage drop on the sense resistors) corresponding to the peak of

the current sine wave (microstepping operation):

Equation 1

The sensing resistors can be changed as described in Section 5: How to change the supply

configuration of the board.

3.3

Gate drivers

The configuration of the gate driving circuitry depends on the external MOSFETs

characteristics. The demonstration boards mount the STD25NF10 Power MOSFETs.

Warning:

Important - a wrong gate driving setup may cause spurious

overcurrent failures even if no load is connected to the power

stage.

According to the STD25NF10 datasheet the total gate charge required to turn on the

MOSFET is about 55 nC.

current time of 1000 ns, 64 nC are provided to the gate. The gate current can be changed in

order to speed up or slow down the commutation speed (i.e. the slew rate of the power

stage outputs); in this case the controlled current time should be changed accordingly.

The boards are designed to operate with a VCC voltage of 15 V, so the corresponding value

for the integrated regulator should be set. The UVLO threshold should be 11 V.

At each commutation some voltage oscillations are generated. This noise could trigger the

overcurrent protection. This event is avoided by adding a blanking time after each

commutation.

A blanking time of 500 ns prevents the occurrence of spurious overcurrent detection in most

operative conditions.