15 External Reset The chip is loaded with default values (Page 64 / 76) TMC2225 Power Driver for Stepper Motors Integrated Circuits Datasheet Rev1.15

TMC2225 DATASHEET (Rev. 1.15 / 2023-FEB-16)

15 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 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.

16 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 intern al 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, a frequency of 10 MHz to 16 MHz is recommended for optimum

performance. The duty cycle of the clock signal is uncritical, as long as minimum high or low input

time for the pin is satisfied (refer to electrical characteristics). Up to 18 MHz can be used, when the

clock duty cycle is 50%. 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, TMC2225 has an internal timeout of 32 internal clocks. In case the external clock

fails, it switches back to internal clock.