Datasheet

TMC2590 DATASHEET (V1.0 / 2019-FEB-22) 49
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13 Power Supply Sequencing
The TMC2590 generates its own 5V supply for all internal operations. The internal reset of the chip is
derived from the supply voltage regulator 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. It
is included in undervoltage detection and reset. Therefore, the startup sequence of the VCC_IO power
supply with respect to VS is not important. VCC_IO may start up before or after VS.
14 System Clock
The system clock is the timing reference for all functions. The internal system clock frequency for all
operations is nominally 14MHz. An external clock of 8MHz to 16MHz 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 TMC2590, 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 16MHz can be supplied. It is recommended to use an external
clock frequency between 10MHz and 14MHz 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. The duty cycle of
the clock signal should be near 50%, especially for high frequencies. Ensure minimum high or low
input time for the pin (refer to electrical characteristics).
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.
To avoid the risk of motor overcurrent upon clock input fail, enable the clock failsafe function by
setting EN_S2VS bit. This bit at the same time enables the low side overcurrent and short protection.