Datasheet

TMC262 / TMC262C DATASHEET (Rev. 2.22 / 2019-FEB-22) 47
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13 System Clock
The system clock is the timing reference for all functions. The internal system clock frequency for all
operations is nominally 15MHz. An external clock of 8MHz to 20MHz can be supplied for more exact
timing, especially when using CoolStep and StallGuard2.
USING THE INTERNAL CLOCK
To use the on-chip oscillator of the TMC262, 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.
Hint
In case well defined precise motor chopper operation are desired, it is supposed to work with an
external clock source.
USING EXTERNAL CLOCK
An external clock frequency of up to 20MHz can be supplied (up to 16MHz for first batch of TMC262C,
production date 1837). It is recommended to use an external clock frequency between 10MHz and
16MHz for best performance. Pay attention to using a near 50% duty-cycle. 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 lead to short impulses and can
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. 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.
The TMC262C provides a clock failover option to switch back to internal clock, in case of the external
clock failing. The function is coupled to enabling short to VS protection (EN_S2VS).
Status
Description
Range
Comment
EN_S2VS
Set this bit to enable protection against a failing
external CLK source. If set, the IC switches back
to external clock after 32 to 48 internal clock
cycles. At the same time, this bit controls the
higher side short detector sensitivity
0 / 1
Undervoltage level
0: Stopping clock will
stop the IC.
1: CLK fail safe
protection