Datasheet

TMC2660 DATASHEET (Rev. 1.05 / 2016-JUL-14) 41
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12 Power Supply Sequencing
The TMC2660 generates its own 5V supply for all internal operations. The internal reset of the chip is
derived from the supply voltage regulators in order to ensure a clean start-up of the device after
power up. During start up, the SPI unit is in reset and cannot be addressed. All registers become
cleared.
VCC_IO limits the voltage allowable on the inputs and outputs and is used for driving the outputs,
but input levels thresholds are not depending on the actual level of VCC_IO. Therefore, the startup
sequence of the VCC_IO power supply with respect to VS is not important.
13 System Clock
The clock is the timing reference for all functions. The internal system clock frequency for all
operations is nominally 15MHz. An external clock of 10MHz to 20MHz can be supplied for more exact
timing, especially when using coolStep and stallGuard2.
USING THE INTERNAL CLOCK FREQUENCY
To use the on-chip oscillator of the TMC2660, tie CLK to GND near the chip. The actual on-chip
oscillator clock frequency can be determined by measuring the delay time between the last step and
assertion of the STST (standstill) status bit, which is 2
20
clocks. There is some delay in reading the
STST bit through the SPI interface, but it is easily 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.
In case well defined precise motor chopper operation are desired, it is supposed to work with an
external clock source.
USING THE EXTERNAL CLOCK FREQUENCY
An external clock frequency of up to 20MHz can be supplied. It is recommended to use an external
clock frequency between 10MHz and 16MHz for best performance. The external clock is enabled and
the on-chip oscillator is disabled with the first logic high driven on the CLK input.
Attention:
Never leave the external clock input floating. It is not allowed to remain within the transition region
(between valid low and high levels), as spurious clock signals might corrupt internal logic state.
Provide an external pull down resistor, in case the driver pin (i.e. microcontroller output) does not
provide a safe level directly after power up. When repeatedly starting and stopping the clock, a clean
clock switch over is important in order to avoid any clock period shorter than the minimum clock
time.
If the external clock is suspended or disabled after the internal 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.