MCT8317A datasheet(36/161 Pages) TI1

36 / 161 page

The duty cycle during align is defined by ALIGN_DUTY. In MCT8317A, current limit during align is

configured through OL_ILIMIT_CONFIG and is determined by ILIMIT or OL_ILIMIT based on configuration of

OL_ILIMIT_CONFIG.

A fast change in the phase current during align may result in a sudden change in the driving torque and this

could result in acoustic noise. To avoid this, the MCT8317A ramps up duty cycle from 0 to until it reaches

ALIGN_DUTY at a configurable rate set by ALIGN_RAMP_RATE. At the end of align routine, the motor will be

aligned at the known position.

8.3.9.4.2 Double Align

Double align is enabled by configuring MTR_STARTUP to 01b. Single align is not reliable when the initial

position of the rotor is 180o out of phase with the applied phase pattern. In this case, it is possible to have

start-up failures using single align. In order to improve the reliabilty of align based start-up, the MCT8317A

provides the option of double align start-up. In double align start-up, MCT8317A uses a phase pattern for the

second align that is 60o out of phase with the first align phase pattern in the commanded direction. In double

align, relevant parameters like align time, current limit, ramp rate are the same as in the case of single align -

two different phase patterns are applied in succession with the same parameters to ensure that the motor will be

aligned to a known position irrespective of initial rotor position.

8.3.9.4.3 Initial Position Detection (IPD)

Initial Position Detection (IPD) can be enabled by configuring MTR_STARTUP to 10b. In IPD, inductive sense

method is used to determine the initial position of the motor using the spatial variation in the motor inductance.

Align or double align may result in the motor spinning in the reverse direction before starting open loop

acceleration. IPD can be used in such applications where reverse rotation of the motor is unacceptable. IPD

does not wait for the motor to align with the commutation and therefore can allow for a faster motor start-up

sequence. IPD works well when the inductance of the motor varies as a function of position. IPD works by

pulsing current in to the motor and hence can generate acoustics which must be taken into account when

determining the best start-up method for a particular application.

8.3.9.4.3.1 IPD Operation

IPD operates by sequentially applying six different phase patterns according to the following sequence:

BC-> CB-> AB-> BA-> CA-> AC (see Figure 8-21). When the current reaches the threshold configured by

IPD_CURR_THR, the MCT8317A stops driving the particular phase pattern and measures the time taken to

reach the current threshold from when the particular phase pattern was applied. Thus, the time taken to reach

IPD_CURR_THR is measured for all six phase patterns - this time varies as a function of the inductance in

the motor windings. The state with the shortest time represents the state with the minimum inductance. The

minimum inductance is because of the alignment of the north pole of the motor with this particular driving state.

MCT8317A

SLLSFQ2 – JANUARY 2023

www.ti.com

Submit Document Feedback

Product Folder Links: MCT8317A

MCT8317A датащи(PDF) 36 Page - Texas Instruments