Datasheet

TMC5041 DATASHEET (Rev. 1.13 / 2017-MAY-16) 44
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7.5 Flags in stealthChop
7.5.1 Open Load Flags
In stealthChop mode, status information is different from the cycle-by-cycle regulated chopper modes.
OLA and OLB show if the current regulation sees that the nominal current can be reached on both
coils.
- A flickering OLA or OLB can result from tiny asymmetries in the sense resistors or in the
motor coils.
- An interrupted motor coil leads to a continuously active open load flag for the coil.
- Both flags are active, if the current regulation did not succeed in scaling up to the full target
current within the last few fullsteps (because no motor is attached or a high acceleration
required a quick action of the current regulator).
With automatic scaling and PWM_GRAD > 1, the current regulation tries to increase the current
quickly to reach the target current in the interrupted motor coil. At the same time but a bit
slower the current regulation tries to decrease the motor current due to the other motor coil
seeing too high current.
Therefore it is recommended to do an on-demand open load test using the spreadCycle or classic
chopper prior to operation in stealthChop, and not to switch on stealthChop in case of open load
failure. Alternatively, PWM_SCALE can be checked for plausible values.
7.5.2 PWM_SCALE Informs about the Motor State
Information about the motor state is available with automatic scaling by reading out PWM_SCALE. 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 value allows seeing the motor load (similar to stallGuard2) and
finding out if the target current can be reached. It even gives an idea on the motor temperature
(evaluate at a well-known state of operation).