NSD-2101 Datasheet, PDF (15/22 Pages) ams AG – Piezo Motor Driver ASIC for SQL-RV Series Reduced Voltage SQUIGGLE® RV and UTAF™ Motors

NSD-2101
Data Sheet - Application Information
8.1 Integration with SQL-RV-1.8 SQUIGGLE Motor
Communicating with the NSD-2101.
The address of the NSD-2101 is 54h (unless the ADR pin is held high in which case the address would be 55h).
I²C supports 8 data bits and 1 acknowledge bit for a total of 9 bits or clock cycles per byte. When attempting to select a device, the first byte
transmitted by the master contains the device address. This address occupies the upper 7 data bits with data bit 0 having a value of zero which
indicates a write operation (theNSD-2101 does not support a read operation).
Therefore when addressing the NSD-2101 the actual value sent by the host during the first 8 SCL (clock) cycles would be A8h (or AAh if ADR pin
high). If the NSD-2101 is powered and connected properly to the SDA/SCL lines then on the 9th clock pulse, the NSD-2101 will hold the data line
low (acknowledge).
The second byte transmitted must be the number of the register to be written. For example, if attempting to send a pulse count, then the register
value would be 2.
The third and any subsequent bytes are the values to be written to the specified register and, if more than three bytes are being sent, the
following registers in increasing order.
If the following data were sent over the I²C bus:
A80277FF
Then registers 02 and 03 of the NSD-2101 would receive values of 77h and FFh respectively.
Supporting More Than Two NSD-2101s on a Single I²C Bus.
To support more than two NSD-2101 drivers on the same I²C bus, the ADR pin may be used as a chip select. That is, one driver is held low by
the host and on all others it is held high. The host then sends commands to the driver with ADR held low. This of course requires that there be a
separate chip select line for each NSD-2101.
How Motion is Generated.
Motion is initiated by directing the NSD-2101 to issue pulses to the motor. In the case of the SQL-RV-1.8 motor, to get any motion, the interval
between the start of each pulse (i.e. the period) must be within some tolerance (e.g. ±2KHz) of the resonant frequency of the motor (e.g. ~172
kHz).
The closer this period is to the resonant frequency of the motor, the more speed/push force is available. Keep in mind that this is a friction drive
which means the amount of motion is dependent on supply voltage, applied frequency vs. actual resonant frequency and the load on the motor.
From an idle state, a minimum of 5 to 10 pulses are required to build up enough orbital motion (of the nut about the screw) to advance the screw.
The minimum pulse count varies with load (higher load, more pulses) and whether or not motion is against or with the load (more against, fewer
with).
As shown in Figure 3, the drive signal is composed of two waveforms (square waves) and each waveform may be full or half bridge. In the case
of the SQL motor, these waveforms are 90 degrees out of phase (in keeping with the geometry of the nut). The phase that leads determines the
direction of motion (direction is set by the host using a bit from the pulse count register).
By default the pulse width of each waveform is 50% of the period (i.e. if register 04 is zero; e.g. pulse with would be 2.9 µsec if the period is 5.8
µsec). But you can adjust the pulse width as one means to regulate speed. The shorter the pulse width (below 50% of the period), the less time
the piezo has to change shape and thus the amount of engagement between nut and screw is reduced.
The default phase shift between waveforms is 25% of the period (i.e. if register 05 is zero). This can also be adjusted and would be for other
motor geometries but in the case of the SQL-RV-1.8; 25% is recommended.
A second means to adjust speed is to set the ratio of full bridge pulses to half bridge pulses (Hybrid Speed Control). This effectively sets the
average voltage seen by the motor. If the supply is 3V then in full bridge the motor “sees” 6V. But if the hybrid speed is 33% then, on an average,
the motor sees 4V.
Note:
Due to dissipation limitations of the driver chip, the maximum supply voltage for full bridge operation is 4.5V (9V to the piezo). Although
the driver supports a supply of up to 5.5V, at any level above 4.5V, the output needs to be half bridge. Within that limitation the hybrid
speed control is more power efficient than the pulse width control method of the regulating speed since the amount of switching into the
capacitive load of the motor is being reduced.
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