MC3PHAC Monolithic Intelligent Motor Controller, Rev. 2

16

Freescale Semiconductor

Operation

Operation

The MC3PHAC motor controller will operate in two modes. The first is standalone operation, whereby the

MC3PHAC can be used without any intervention from an external personal computer. In standalone

mode, the MC3PHAC is initialized by passive devices connected to the MC3PHAC and input to the

system at power-up/reset time. In standalone mode, some parameters continue to be input to the system

as it operates. Speed, PWM frequency, bus voltage, and acceleration parameters are input to the system

on a real-time basis.

The second mode of operation is called PC master software mode.That operational mode requires the

use of a personal computer and PC master software executing on the personal computer, communicating

with the MC3PHAC, or a microcontroller emulating PC master software commands. All command and

setup information is input to the MC3PHAC via the PC host.

Standalone Operation

If the VBOOST_MODE pin is high when the MC3PHAC is powered up, or after a reset, the MC3PHAC

enters standalone mode. In this mode of operation, the functionality of many of the MC3PHAC pins

change so that the device can control a motor without requiring setup information from an external master.

When operated in standalone mode, the MC3PHAC will drive certain pins corresponding to parameters

which must be specified, while simultaneously monitoring the response on other pins.

In many cases, the parameter to be specified is represented as an analog voltage presented to the

MUX_IN pin, while certain other pins are driven low. In so doing, the MC3PHAC can accommodate an

external analog mux which will switch various signals on the MUX_IN pin when the signal select line goes

passive network can be connected to each of the parameter select output pins and the MUX_IN pin, as

shown in Figure 8.

The Thevenin equivalent impedance of this passive network as seen by the MUX_IN pin is very important

and should be in the range of 5 k

Ω to 10 kΩ. If the resistance is too high, leakage current from the

input/output (I/O) pins will cause an offset voltage that will affect the accuracy of the reading. If the

resistance is too low, the parameter select pins will not be able to sink the required current for an accurate

reading. Using a pullup resistor value of 6.8 k

Ω (as indicated in Figure 8), the resulting value for each

parameter as a function of the corresponding pulldown resistor value is shown in Figure 9, Figure 10,

Figure 11, and Table 4.

The START input pin is debounced internally and a switch can be directly accommodated on this pin. The

input is level sensitive, but a logic 1 level must exist on the pin before a logic 0 level will be processed as

a start signal. This will prevent an accidental motor startup in the event of the MC3PHAC being powered

up, where the switch was left in the start position.

The FWD input pin is debounced internally and can directly accommodate a switch connection. The input

is also level sensitive.

Figure 8 shows the jumper arrangement connected to the PWMPOL_BASEFREQ input pin. For proper

operation, one and only one jumper connection can be made at any given time. Table 3 shows the polarity

and base frequency selections as a function of the jumper connection.