TMC262-EVAL 参数 Datasheet PDF下载

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

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13 System Clock

The internal system clock frequency for all operations is nominally 15MHz. An external clock of 10MHz

to 20MHz (16MHz recommended for optimum performance) can be supplied for more exact timing,

especially when using coolStep and stallGuard2. Alternatively, the on-chip oscillator clock frequency

can be determined by measuring the delay time between the last step and assertion of the STST

status bit, which is 2

20

clocks. There is some delay in reading the STST bit through the SPI interface,

but it is possible to measure the oscillator frequency within 1%. Chopper timing parameters can then

be corrected using this measurement, because the oscillator is relatively stable over a wide range of

environmental temperatures.

An external clock frequency of up to 20MHz can be supplied. The external clock is enabled and the on-

chip oscillator is disabled with the first logic high driven on the CLK input. To use the on-chip

oscillator, tie CLK to GND near the chip. If the external clock is suspended or disabled after the

oscillator has been disabled, the chip will not operate. Be careful to switch off the power MOSFETs

(by driving the ENN input high or setting the TOFF parameter to 0) before switching off the clock,

because otherwise the chopper would stop and the motor current level could rise uncontrolled. If the

short to GND detection is enabled, it stays active even without clock.

13.1 Frequency Selection

A higher frequency allows faster step rates, faster SPI operation, and higher chopper frequencies. On

the other hand, it may cause more electromagnetic emission and more power dissipation in the

digital logic. Generally, a system clock frequency of 8MHz to 16MHz should be sufficient for most

applications, unless the motor is to operate at the highest velocities. If the application can tolerate

reduced motor velocity and increased chopper noise, a clock frequency of 4MHz to 8MHz should be

considered.

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