With automatic scaling the current regulation checks (Page 42 / 76) TMC2225 Power Driver for Stepper Motors Integrated Circuits Datasheet Rev1.15

TMC2225 DATASHEET (Rev. 1.15 / 2023-FEB-16)

With automatic scaling, the current regulation checks the current in a single coil at a time, only,

measuring the coil with the higher target current. The other coil PWM duty cycle becomes scaled

proportionally. In case a coil connection is interrupted, this behavior can lead to the PWM duty cycl e

increasing to its limit and staying undetected or triggering the overcurrent protection.

To prevent coil overheating or driver damage due to this behavior, do an on -demand open load test

using the SpreadCycle chopper prior to operation in StealthChop, an d do not enable StealthChop in

case of open load failure, or check PWM_SCALE_SUM for a value in the expected range.

Attention

For pwm_autoscale mode, an open load situation on a single coil can lead to the current regulation

algorithm scaling up the non-interrupted coil to too high current values. Therefore, it is recommended

to test for open load prior to operation in StealthChop using SpreadCycle. Do not enable St ealthChop

in case of an open load situation.

6.6.2 PWM_SCALE_SUM Informs about the Motor State

Information about the motor state is available with automatic scaling by reading out

PWM_SCALE_SUM. As this parameter reflects the actual voltage required to drive the target current into

the motor, it depends on several factors: motor load, coil resistance, supply voltage, and current

setting. Therefore, an evaluation of the PWM_SCALE_SUM value allows checking the motor operation

point. When reaching the limit (255), the current regulator cannot sustain the full moto r current, e.g.

due to a drop in supply voltage.

6.7 Freewheeling and Passive Braking

UART

StealthChop provides different options for motor standstill. These options can be enabled by setting

the standstill current IHOLD to zero and choosing the desired option using the FREEWHEEL setting.

The desired option becomes enabled after a time period specified by TPOWERDOWN and

IHOLD_DELAY. Current regulation becomes frozen once the motor target current is at zero current in

order to ensure a quick startup. With the freewheeling options, both freewheeling and passive

braking can be realized. Passive braking is an effective eddy current motor braking, which consumes a

minimum of energy, because no active current is driven into the coils. However, passive braking will

allow slow turning of the motor when a continuous torque is applied.

Hint

Operate the motor within your application when exploring StealthChop. Motor performance often is

better with a mechanical load, because it prevents the motor from stalling due mechanical oscillations

which can occur without load.