Datasheet

TMC2209 DATASHEET (Rev. 1.03 / 2019-JUN-26) 71
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17 External Reset
The chip is loaded with default values during power on via its internal power-on reset. Some of the
registers are initialized from the OTP at power up. In order to reset the chip to power on defaults,
any of the supply voltages monitored by internal reset circuitry (VS, +5VOUT or VCC_IO) must be
cycled. As +5VOUT is the output of the internal voltage regulator, it cannot be cycled via an external
source except by cycling VS. It is easiest and safest to cycle VCC_IO in order to completely reset the
chip. Also, current consumed from VCC_IO is low and therefore it has simple driving requirements.
Due to the input protection diodes not allowing the digital inputs to rise above VCC_IO level, all
inputs must be driven low during this reset operation. When this is not possible, an input protection
resistor may be used to limit current flowing into the related inputs.
18 Clock Oscillator and Input
The clock is the timing reference for all functions: the chopper frequency, the blank time, the standstill
power down timing, and the internal step pulse generator etc. The on-chip clock oscillator is
calibrated in order to provide timing precise enough for most operation cases.
USING THE INTERNAL CLOCK
Directly tie the CLK input to GND near to the IC if the internal clock oscillator is to be used. The
internal clock frequency is factory-trimmed to 12MHz by OTP programming.
USING AN EXTERNAL CLOCK
When an external clock is available, any frequency of 8 to 13.4MHz (max. 16MHz) can be used to clock
the TMC2209. The duty cycle of the clock signal has to be near 50%, especially for high frequencies.
Ensure minimum high or low input time for the pin (refer to electrical characteristics). Make sure, that
the clock source supplies clean CMOS output logic levels and steep slopes when using a high clock
frequency. The external clock input is enabled with the first positive polarity seen on the CLK input.
Modifying the clock frequency is an easy way to adapt the StealthChop chopper frequency or to
synchronize multiple drivers. Working with a very low clock frequency down to 4 MHz can help
reducing power consumption and electromagnetic emissions, but it will sacrifice some performance.
Use an external clock source to synchronize multiple drivers, or to get precise motor operation with
the internal pulse generator for motion. The external clock frequency selection also allows modifying
the power down timing and the chopper frequency.
Hint
Switching off the external clock frequency would stop the chopper and could lead to an overcurrent
condition. Therefore, TMC2209 has an internal timeout of 32 internal clocks. In case the external clock
fails, it switches back to internal clock.