3 Device configuration
This section offers an overview of the basic configuration steps which are required for make the demonstration
board operative. More details about the configuration of the gate driving circuitry and the control algorithms are
available in the specific application notes.
Important: The device configuration is mandatory; the default configuration is not operative.
Before changing the device configuration verify that the device is in high impedance status (power stage is
disabled).
3.1 Voltage mode driving
When the device uses the voltage mode driving, the shunt resistors are not required. In this case it is
recommended to remove the shunt resistors (R4 - R8) and short the sense pins to ground through the JP1
and JP2 jumpers.
The configuration parameters of the voltage mode driving can be obtained through the BEMF compensation tool
embedded into the SPINFamily software.
The incorrect setup of these parameters could cause several issues, in particular:
• the phase current decreases with the speed and the motor stalls
• 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 (rms 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 SPIN family software a step-by-step procedure is explained. The same procedure can
also be found in application note AN4144: “Voltage mode control operation and parameter optimization”.
Click on the [evaluate] button to get the suggested setup for the voltage mode driving. Then click on the [write]
button to copy the data into the registers of the powerSTEP01.
3.2
Advanced current control
The following configuration gives good results with most motors:
• Minimum ON time = (2 x t
CC
+ t
DT
+ t
BLANK
) + 1 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 disabled
The impact of the timing parameters is 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 reference voltage (i.e.,
the voltage drop on the sense resistors) corresponding to the peak of the current sine wave (microstepping
operation):
I
peak
=
TVAL_X
R
sense
=
TVAL_X
0.033
(1)
The sensing resistors can be changed as described in Section 5 .
UM1829
Device configuration
UM1829 - Rev 2
page 9/21
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