TMC262-EVAL 参数 Datasheet PDF下载

TMC262 DATASHEET (Rev. 2.07 / 2013-FEB-14)

10

Status word

SG

Description

10-bit

unsigned

integer

stallGuard2

measurement value. A higher value indicates

lower mechanical load. A lower value indicates

a higher load and therefore a higher load angle.

For stall detection, adjust SGT to return an SG

value of 0 or slightly higher upon maximum

motor load before stall.

Range

0… 1023

Comment

0: highest load

low value: high load

high value: less load

4.1 Tuning the stallGuard2 Threshold

Due to the dependency of the stallGuard2 value SG from motor-specific characteristics and application-

specific demands on load and velocity the easiest way to tune the stallGuard2 threshold

SGT

for a

specific motor type and operating conditions is interactive tuning in the actual application.

The procedure is:

1.

2.

Operate the motor at a reasonable velocity for your application and monitor SG.

Apply slowly increasing mechanical load to the motor. If the motor stalls before SG reaches

zero, decrease SGT. If SG reaches zero before the motor stalls, increase SGT. A good SGT

starting value is zero. SGT is signed, so it can have negative or positive values.

The optimum setting is reached when SG is between 0 and 400 at increasing load shortly

before the motor stalls, and SG increases by 100 or more without load. SGT in most cases can

be tuned together with the motion velocity in a way that SG goes to zero when the motor

stalls and the stall output SG_TST is asserted. This indicates that a step has been lost.

3.

The system clock frequency affects SG. An external crystal-stabilized clock should be used for

applications that demand the highest performance. The power supply voltage also affects SG, so

tighter regulation results in more accurate values. SG measurement has a high resolution, and there

are a few ways to enhance its accuracy, as described in the following sections.

4.1.1 Variable Velocity Operation

Across a range of velocities, on-the-fly adjustment of the stallGuard2 threshold SGT improves the

accuracy of the load measurement SG. This also improves the power reduction provided by coolStep,

which is driven by SG. Linear interpolation between two SGT values optimized at different velocities is

a simple algorithm for obtaining most of the benefits of on-the-fly SGT adjustment, as shown in

red.

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