AN-030: Three Phase Stepper with TMC5062

Abstract

The TMC5062 supports driving up to two three phase stepper motors. This application note describes the additional register settings available in the TMC5062 for three phase motor operation.

Additionally, it covers the option bits to change the microstep resolution for TMC5062 and TMC5031 (see Table 1.2). This allows increasing the effective acceleration rate, e.g., a half microstep gives double velocity and acceleration rate.

Three Phase Motor Operation

The TMC5062 is prepared to drive three phase motors. However, three phase motors are not often found in stepper drives, but they provide an additional smoothness at low velocity operation due to a lower intrinsic detent torque. The following chapters show additional information adding to the TMC5062 datasheet in order to provide the required settings. For three phase motors, the TMC5062 also supports stallGuard as well as coolStep, but dcStep is only available with two phase steppers.

TMC5062 three phase section is identical to the TMC389.

Three Phase Motor Application

In a three phase motor application, only three half bridges and a single sense resistor are required to drive a stepper motor. One or both motor drivers can be configured for driving a three phase motor. It is important to match the external wiring before switching on this option of the power driver stage. Do not enable a two phase setting with a three phase motor.

Figure 1.1 Connecting a three phase motor.

Table 1 Driver stage pins showing three phase motor option
Pin	Number	Type	Function
O2A1	14	O (VS)	Motor 2 A1 output (stepper motor coil A), or three phase stepper motor U output.
BR2A	15		Motor 2 bridge A negative power supply and current sense input. Provide external sense resistor to GND.
O2A2	16	O (VS)	Motor 2 A2 output (stepper motor coil A), or three phase stepper motor V output.
VS	17, 19		Driver 2 positive power supply. Connect to VS and provide sufficient filtering capacity for chopper current ripple.
GNDP	18	GND	Power GND for driver 2. Connect to GND.
O2B1	20	O (VS)	Motor 2 B1 output (stepper motor coil B), or three phase stepper motor W output.
BR2B	21		Motor 2 bridge B negative power supply and current sense input. Provide external sense resistor to GND. Connect to BR2A for three phase motor operation.
O2B2	22		Motor 2 B2 output (stepper motor coil B), unused for three phase stepper motor.
O1B2	39		Motor 1 B2 output (stepper motor coil B), unused for three phase stepper motor.
BR1B	40		Motor 1 bridge B negative power supply and current sense input. Provide external sense resistor to GND. Connect to BR1A for three phase motor operation.
01B1	41	O (VS)	Motor 1 B1 output (stepper motor coil B), or three phase stepper motor W output.
VS	42, 44		Driver 1 positive power supply. Connect to VS and provide sufficient filtering capacity for chopper current ripple.
GNDP	43	GND	Power GND for driver 1. Connect to GND.
O1A2	45	O (VS)	Motor 1 A2 output (stepper motor coil A), or three phase stepper motor V output.
BR1A	46		Motor 1 bridge A negative power supply and current sense input. Provide external sense resistor to GND.
O1A1	47	O (VS)	Motor 1 A1 output (stepper motor coil A), or three phase stepper motor U output.

Register Set to support Three Phase Motors

Programmable microstep shapes allow optimizing the motor performance. Both drivers can drive a two- or a three phase stepper motor. In order to drive higher current motors, a parallel mode allows double current for a single driver, by paralleling both output power stages. In order to operate a three phase motor, the MSLUTSTART entry has to be re-initialized to fit the 120° phase shift required for a three phase motor, rather than 180° phase shift for a two phase motor. The settings most important for a three phase motor are highlighted.

MOTOR DRIVER REGISTER SET (MOTOR 1: 0X60 to 0X6F, MOTOR 2: 0X70 to 0X7F)
R/W	Addr	n	Register	Description / bit names	Range [Unit]
W	0x69 0x79	8 + 8	MSLUTSTART	bit 7 to 0: START_SIN bit 23 to 16: START_SIN90_120 START_SIN gives the absolute current at microstep table entry 0. START_SIN90_120 gives the absolute current for microstep table entry at positions 256 resp. 171 for a three phase motor. Start values are transferred to the microstep registers CUR_A and CUR_B, whenever the reference position MSCNT=0 is passed. Attention: Default values are for two phase motor, initialize before first motion with three phase motor!	START_SIN reset default =0 (2ph/3ph) START_SIN90_120 reset default =247 (2ph) Set to 214 for 3 phase motor when using default table.
R	0x6A 0x7A	10	MSCNT	Microstep counter. Indicates actual position in the microstep table for CUR_A. CUR_B uses an offset of 256 (2 phase motor) resp. 171 (3 phase motor). Hint: Move to a position where MSCNT is zero before re-initializing MSLUTSTART or MSLUT and MSLUTSEL.

Table 1.2 Chopper settings bits 31 to 16. Refer separate table for bits 15 to 0 for 3 phase motor
0X6C, 0X7C: CHOPCONF – CHOPPER CONFIGURATION 31 to 16
Bit	Name	Function	Comment
31	ph3sel	1: 3 phase motor	ph3sel=0: 2 phase motor ph3sel=1: 3 phase motor (see Table 1.3)
30	diss2g	short to GND protection disable	0: Short to GND protection is on 1: Short to GND protection is disabled
29	0	Do not use	Set 0
28	intpol16	16 microsteps with interpolation	1: In 16 microstep mode, the microstep resolution becomes extrapolated to 256 microsteps for smoothest motor operation
27	mres3	MRES micro step resolution	%0000: Native 256 microstep setting. Normally use this setting when the IC is operated with the internal ramp generator.
27	mres3		%0001 to %1000: 128, 64, 32, 16, 8, 4, 2, FULLSTEP Reduced microstep resolution. The resolution gives the number of microstep entries per sine quarter wave. Please take care to switch at certain microstep positions, when switching to a low resolution. The switching position determines the sequence of patterns. step width=2^MRES [microsteps] Attention: Optional use to increase effective acceleration in high acceleration applications, only. A 128 microstep setting will double the acceleration range, as the motor operates with double velocity at the same setting as with 256 microsteps. Use carefully. Does not integrate with dcStep.
26	mres2
25	mres1
24	mres0
23	sync3	SYNC PWM synchronization clock	ph3sel=0, only
22	sync2
21	sync1
20	sync0
19	vhighchm	high velocity chopper mode	ph3sel=0, only
18	vhighfs	high velocity fullstep selection	ph3sel=0, only
17	vsense	sense resistor voltage based current scaling	0: Low sensitivity, high sense resistor voltage 1: High sensitivity, low sense resistor voltage
16	tbl1	TBL blank time select	%00 to %11: Set comparator blank time to 16, 24, 36 or 54 clocks Hint: %10 is recommended for most applications

Table 1.3: Chopper settings for three phase motor (bits 15 to 0)
0X6C, 0X7C: CHOPCONF – CHOPPER CONFIGURATION 15 to 0 WITH PH3SEL=1 (3 PHASE MOTOR)
Bit	Name	Function	Comment
15	tbl0		(see tbl1 in bit 16)
14	-	reserved	set to 0
13	rndtf	random TOFF time	0	Chopper off time is fixed as set by TOFF
13	rndtf	random TOFF time	1	Random mode, TOFF is random modulated by dN_CLK= -12 to +3 clocks.
12	csync	chopper synchronization	0	Chopper freely running
12	csync	chopper synchronization	1	Synchronize chopper to full steps 11
11	-	reserved	set to 0
10	nosd3ph		0	Each chopper on-cycle is followed by a slow decay phase as set by TOFF
10	nosd3ph		1	Slow decay phases are skipped between the chopper phases, except directly following a short to GND or chopper synchronization.
9	hyst5	HYST hysteresis value for three phase chopper	DAC hysteresis setting: %00000 to %11111: 0 to 63 (1/512 of this setting adds to current setting) Attention: Effective HYST/2 must be ≤ 255-sinewave peak (248 at max. current setting) – Reduce current setting to 28 for maximum hysteresis. Do not work with too small setting (poor performance). I_RUN=31 requires HYST < 16 I_RUN=30 requires HYST < 32 I_RUN=29 requires HYST < 48 Hint: Hysteresis decrement is done each 16 clocks
8	hyst4
7	hyst3
6	hyst2
5	hyst1
4	hyst0
3	toff3	TOFF off time and driver enable	Off time setting controls duration of slow decay phase N_CLK= 12 + 32*TOFF (Minimum is 64 clocks) %0000: Driver disable, all bridges off %0001: 1 – use only with TBL ≥ 2 %0010 to %1111: 2 to 15
2	toff2
1	toff1
0	toff0

0X6D, 0X7D: COOLCONF – SMART ENERGY CONTROL COOLSTEP AND STALLGUARD2
Bit	Name	Function	Comment
_	-	reserved	set to 0
25	sspd	stallGuard2 speed (3 phase motor only)	0	Standard mode, high time resolution for stallGuard2
25	sspd	stallGuard2 speed (3 phase motor only)	1	stallGuard2 uses more filtering, use for low motor velocity only. Set this bit, if stallGuard value ripple is too high.
24	sfilt	stallGuard2 filter enable	0	Standard mode, high time resolution for stallGuard2
24	sfilt	stallGuard2 filter enable	1	Filtered mode, stallGuard2 signal updated for each four fullsteps (resp. six fullsteps for 3 phase motor) only to compensate for motor pole tolerances
23	-	reserved	set to 0
22	stallGuard2 threshold value	stallGuard2 threshold value	This signed value controls stallGuard2 level for stall output and sets the optimum measurement range for readout. A lower value gives a higher sensitivity. Zero is the starting value working with most motors. -64 to +63: A higher value makes stallGuard2 less sensitive and requires more torque to indicate a stall.
21
20
19
18
17
16
15	seimin	minimum current for smart current control	0: 1/2 of current setting (IRUN) 1: 1/4 of current setting (IRUN)
14	sedn1	current down step speed	%00: For each 32 stallGuard2 values decrease by one %01: For each 8 stallGuard2 values decrease by one %10: For each 2 stallGuard2 values decrease by one %11: For each stallGuard2 value decrease by one
13	sedn0	current down step speed
12	-	reserved	set to 0
11	semax3	stallGuard2 hysteresis value for smart current control	If the stallGuard2 result is equal to or above (SEMIN+SEMAX+1)*32, the motor current becomes decreased to save energy. %0000 to %1111: 0 to 15
10	semax2
9	semax1
8	semax0
7	-	reserved	set to 0
6	seup1	current up step width	Current increment steps per measured stallGuard2 value %00 to %11: 1, 2, 4, 8
5	seup0	current up step width
4	-	reserved	set to 0
3	semin3	minimum stallGuard2 value for smart current control and smart current enable	If the stallGuard2 result falls below SEMIN*32, the motor current becomes increased to reduce motor load angle. %0000: smart current control coolStep off %0001 to %1111: 1 to .15
2	semin2
1	semin1
0	semin0

0X6F, 0X7F: DRV_STATUS – STALLGUARD2 VALUE AND DRIVER ERROR FLAGS
Bit	Name	Function	Comment
31	stst	standstill indicator	This flag indicates motor stand still in each operation mode. It is especially useful for step & dir mode.
30	olb	open load indicator phase B	1: Open load detected on phase A or B or on any phase for a three phase motor. Hint: This is just an informative flag. The driver takes no action upon it. False detection may occur in fast motion and standstill. Check during slow motion, only.
29	ola	open load indicator phase A
28	s2gb	short to ground indicator phase B	1: Short to GND detected on phase A or B or on any phase for a three phase motor. The driver becomes disabled. The flags stay active, until the driver is disabled by software or by the ENN input
27	s2ga	short to ground indicator phase B
26	otpw	overtemperature pre-warning flag	1: Overtemperature pre-warning threshold is exceeded. The overtemperature pre-warning flag is common for both drivers.
25	ot	overtemperature flag	1: Overtemperature limit has been reached. Drivers become disabled until otpw is also cleared due to cooling down of the IC. The overtemperature flag is common for both drivers.
24	stallGuard	stallGuard2 status	1: Motor stall detected (SG_RESULT=0)
23	-	reserved	Ignore these bits
22
21
20	CS ACTUAL	actual motor current / smart energy current	Actual current control scaling, for monitoring smart energy current scaling controlled via settings in register COOLCONF.
19
18
17
16
15	fsactive	full step active indicator	1: Indicates that the driver has switched to fullstep as defined by chopper mode settings and velocity thresholds
14	-	reserved	Ignore these bits
13
12
11
10
9	SG_ RESULT	stallGuard2 result respectively PWM on time for coil A in stand still for motor temperature detection	Mechanical load measurement: The stallGuard2 result gives a means to measure mechanical motor load. A higher value means lower mechanical load. A value of 0 signals highest load. With optimum SGT setting, this is an indicator for a motor stall. The stall detection compares SG_RESULT to 0 in order to detect a stall. SG_RESULT is used as a base for coolStep operation, by comparing it to a programmable upper and a lower limit. SG_RESULT is not applicable when dcStep is active – stallGuard2 works best with microstep operation. Temperature measurement: In standstill, no stallGuard2 result can be obtained. SG_RESULT shows the chopper on-time for motor coil A instead. If the motor is moved to a determined microstep position at a certain current setting, a comparison of the chopper on-time can help to get a rough estimation of motor temperature. As the motor heats up, its coil resistance rises and the chopper on-time increases.
8
7
6
5
4
3
2
1
0

spreadCycle 3-Phase Motor Chopper

The spreadCycle chopper scheme for three phase motors (pat.fil.) is a precise and simple to use chopper principle, which automatically determines the optimum fast decay portion for the motor. Anyhow, a number of settings can be made in order to optimally fit the driver to the motor.

Three parameters control the chopper scheme for a three phase motor:

Parameter	Description	Setting	Comment
HYST	The hysteresis setting is the main control for the chopper and determines the chopper frequency. A higher setting introduces more current ripple and thus reduces frequency. A too low setting will result in the coil current only loosely following the target current and thus reduced microstep performance, especially in the current zero crossing. A too high setting can cause audible chopper noise. In order to use the full hysteresis range, be careful to set motor current to max. 28.	0 to 63	Hysteresis for the chopper
nosd	Selection of the TOFF insertion	0	Use TOFF setting for ad-ditional slow decay phases
nosd	Selection of the TOFF insertion	1	No slow decay phase
csync	This bit switches on chopper synchronization. If enabled, the chopper engine becomes reset with each motor fullstep, in order to avoid a beat occurring between full step sequence and chopper clock.	0	Chopper runs freely
csync		1	Synchronization enable
TOFF	Sets the slow decay time (off time). This setting also limits the maximum chopper frequency. For most 3-phase motor applications an off time will not be required. In this case, a dummy value needs to be programmed to this register to enable the driver and the nosd flag shall be set. Setting this parameter to zero completely disables all driver transistors and the motor can free-wheel.	0	Chopper off

Each chopper cycle is comprised of an on phase, a fast decay phase and a slow decay phase (see Figure 1.2). Optional additional slow decay phases can be added (switch off using nosd bit). The hysteresis determines the chopper frequency by forcing the driver to introduce some amount of current ripple into the motor coils. The motor inductivity determines the ability to follow a changing motor current. The duration of the on- and fast decay phase needs to cover at least the blank time, because the current comparator is disabled during this time.

EXPERIMENTING WITH THE MOTOR

The setting can also be determined by experimenting with the motor: a too low setting will result in reduced microstep accuracy, while a too high setting will lead to more chopper noise and motor power dissipation. The correct setting can be determined best by rotating the motor slowly, and increasing hysteresis setting, until the motion of the motor is very smooth (feel with fingers or add a long pointer to the axis, e.g. laser pointer).

MEASURING MOTOR CURRENTS AT THE SENSE RESISTORS

Alternatively you can measure the motor currents at the sense resistor with a current probe or with an oscilloscope. Check the waves for a pure sine wave. A further increment of the hysteresis setting will lower the chopper frequency and might generate audible chopper noise at some point.

Figure 1.2 spreadCycle 3 phase chopper scheme showing the coil current within a chopper cycle.