Current and chopper

How the driver sets the coil current from the motor's datasheet, and how to choose between SpreadCycle, StealthChop, CoolStep and DcStep.

Coil current

Three settings multiply to the coil current:

I_RMS = (GLOBAL_SCALER / 256) × ((CS + 1) / 32) × V_FS / R_SENSE / √2

with CS = IRUN while moving and IHOLD at standstill, and V_FS = 325 mV typical. GLOBAL_SCALER is 32 to 255 (0 means 256; 1 to 31 are not allowed), IRUN and IHOLD are 0 to 31.

You do not compute these. Fill DriverConfig::motor_spec and Initialize() (or motorControl.ConfigureMotorCurrent()) does it:

MotorSpec field	Meaning	Default
rated_current_ma	Motor rated current, RMS	1500
run_current_ma	Run current; 0 uses the rated current	0
hold_current_ma	Standstill current; 0 uses 30 % of the run current	0
sense_resistor_mohm	RSENSE on your board	50
supply_voltage_mv	VS	24000
steps_per_rev	Full steps per revolution	200
winding_resistance_mohm, winding_inductance_mh	Used for the StealthChop limits	3, 0
iholddelay_ms	Time to ramp from run to hold current at standstill	100
scaler_adjustment_percent, irun_adjustment_percent, ihold_adjustment_percent	Trim the calculated values	0

The calculation starts at IRUN = 31 and solves for GLOBAL_SCALER; when the scaler would exceed 200 it lowers IRUN (not below 16) to keep the scaler in range. A run current more than 10 % above the full-scale current of the sense resistor fails. With 50 mΩ and 1500 mA the result is IRUN = 31, GLOBAL_SCALER ≈ 84 (derived). LogDerivedInitSummary() prints what was written; motorControl.SetCurrent(irun, ihold) and SetGlobalScaler() set the registers directly.

TMC5130

The TMC5130 has no GLOBAL_SCALER. On a TMC5130 the driver never writes it and calculates IRUN / IHOLD from the TMC5130's own formula (TMC5130).

Choosing a chopper

Mode	What it does	Choose it for	Limits
StealthChop2	Voltage-mode PWM, near silent	Low and medium speed, standstill	No StallGuard2; the first motion after power-up calibrates it (IRUN ≥ 8)
SpreadCycle	Cycle-by-cycle current control	High speed, high dynamics, any load	Audible chopper noise at low speed
CoolStep	Lowers the current while StallGuard2 reports a light load	Saving energy and heat	Needs SpreadCycle above TCOOLTHRS
DcStep	Lets the motor slow down under overload instead of losing steps	Variable loads near the torque limit	Above VDCMIN; set it up with the datasheet

DriverConfig::global_config.en_stealthchop_mode (on by default) selects StealthChop. The chip then switches by speed, measured as TSTEP (the time between microsteps):

Threshold	Register	Above this speed
StealthChop to SpreadCycle	TPWMTHRS	SpreadCycle
CoolStep and StallGuard2 active	TCOOLTHRS	CoolStep and the stall output work
High-speed mode	THIGH	Full step (vhighfs) or classic chopper (vhighchm)

Set the three at once in physical units with thresholds.SetModeChangeSpeeds(), or one at a time with SetStealthChopVelocityThreshold(), SetTcoolthrs() and SetHighSpeedThreshold().

// Switch between StealthChop (quiet, low speed), SpreadCycle and full step by speed.
driver.thresholds.SetModeChangeSpeeds(1.0f, 0.5f, 5.0f, Unit::RevPerSec);   // TPWMTHRS, TCOOLTHRS, THIGH

// CoolStep: lower the current while the load is light (needs SpreadCycle and TCOOLTHRS).
tmc51x0::CoolStepConfig cool{};
cool.lower_threshold_sg = 100;
cool.upper_threshold_sg = 300;
cool.min_velocity = 0.5f;
cool.velocity_unit = Unit::RevPerSec;
driver.motorControl.ConfigureCoolStep(cool);

// Change the run and hold currents (IRUN, IHOLD: 0..31 of the GLOBAL_SCALER full scale).
driver.motorControl.SetCurrent(20, 8);

SpreadCycle timing

ChopperConfig holds the CHOPCONF fields. The driver's defaults (TOFF = 5, TBL = 2, HSTRT = 4, HEND = 0) work for most motors; tune HSTRT and HEND with the datasheet's procedure (chapter 7) when the motor is noisy or the current waveform is distorted. mres sets the microstep resolution (256 down to full step) and intpol interpolates lower resolutions to 256 microsteps.

StealthChop PWM frequency

StealthChopConfig::pwm_freq selects f_PWM as a fraction of f_CLK:

pwm_freq	fPWM	At 12 MHz
0	2/1024 fCLK	23.4 kHz
1 (default)	2/683 fCLK	35.1 kHz
2	2/512 fCLK	46.9 kHz
3	2/410 fCLK	58.5 kHz

Automatic tuning (pwm_autoscale, pwm_autograd) needs a run current of IRUN ≥ 8 and a first move at moderate speed. Changing GLOBAL_SCALER or VS afterwards invalidates the tuning until the chip re-tunes.

Power stage (TMC5160)

The TMC5160 drives external MOSFETs. PowerStageParameters sets the gate drive from MOSFET data:

Field	Sets	Default
mosfet_miller_charge_nc	DRVSTRENGTH (gate current 200 mA to 600 mA low side)	10 nC
bbm_time_ns	Break-before-make time, BBMTIME / BBMCLKS	100 ns
sense_filter	FILT_ISENSE	100 ns
over_temp_protection	OTSELECT	150 °C
s2vs_voltage_mv, s2g_voltage_mv, shortfilter, short_detection_delay_us_x10	SHORT_CONF	0 = chip default

Next: StallGuard and homing.