TMC5160 DATASHEET (Rev. 1.08 / 2018-NOV-19)
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25 External Reset
The chip is loaded with default values during power on via its internal power-on reset. In order to
reset the chip to power on defaults, any of the supply voltages monitored by internal reset circuitry
(VSA, +5VOUT or VCC_IO) must be cycled. VCC is not monitored. Therefore VCC must not be switched
off during operation of the chip. As +5VOUT is the output of the internal voltage regulator, it cannot
be cycled via an external source except by cycling VSA. 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.
In case, VCC becomes supplied by an external source, make sure that VCC is at a stable value above
the lower operation limit once the reset ends. This normally is satisfied when generating a 3.3V
VCC_IO from the +5V supply supplying the VCC pin, because it will then come up with a certain delay.
26 Clock Oscillator and Input
The clock is the timing reference for all functions: the chopper, the velocity, the acceleration control,
etc. Many parameters are scaled with the clock frequency, thus a precise reference allows a more
deterministic result. The factory-trimmed on-chip clock oscillator provides timing in case no external
clock is easily available.
26.1 Using the Internal Clock
Directly tie the CLK input to GND near to the IC if the internal clock oscillator is to be used. It will be
sufficient for applications, where a velocity precision of roughly +-4% is tolerable.
26.2 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 second
positive polarity seen on the CLK input.
Hint
Switching off the external clock frequency prevents the driver from operating normally. Therefore an
internal watchdog switches back to internal clock in case the external signal is missing for more than
roughly 32 internal clock cycles.
26.2.1 Considerations on the Frequency
A higher frequency allows faster step rates, faster SPI operation and higher chopper frequencies. On
the other hand, it causes more power dissipation in the TMC5160 digital core and 5V voltage
regulator. Generally a frequency of 10 MHz to 12 MHz should be sufficient for most applications. At
higher clock frequency, the VSA supply voltage should be connected to a lower voltage for
applications working at more than 24V nominal supply voltage. For reduced requirements concerning
the motor dynamics, a clock frequency of down to 8 MHz (or even lower) can be considered.
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