L6238 datasheet(12/35 Pages) STMICROELECTRONICS

12 / 35 page

masked out, and when it is low, the Bemf informa-

tion can be detected normally. When the motor

has reached a predetermined speed, the SE-

QUENCE INCREMENT pin can be left low and

the L6238 Motor Control logic will take over and

automatically bring the motor into Phase Lock.

3,0 START-UP ALGORITHMS

3.1 Spin-Up Operation

The spin operation can be separated into 3 parts:

1) Open Loop Start-Up - The object is to create

motion in the desired direction so that the Bemf

voltages at the 3 motor terminals can provide reli-

able information enabling a transition to closed

loop operation.

2) Closed Loop Start-Up - The Bemf voltage

zerocrossings provide timing information so that

the motor can be accelerated to steady state

speed.

3) Steady-State Operation - The Bemf voltage

zero-crossings provide timing information for pre-

cision speed control.

The L6238 contains features that offer flexible

control over the start-up procedure. Either the on-

board Auto-Start Algorithm can be used to control

the start-up sequence or more sophisticated exte-

mal start-up algorithms can be developed using

the Serial Port and key control/sense functions

brought out to pins.

3.2 Auto-Start Algorithm

The Serial Port Control Bit

Auto/Ext (Refer to Ta-

ble 2), controls the start-up mode. The power up

default state is a logic high which selects the

AutoStart Mode. When Run/Brake is low, the

L6238 is in brake mode, and the Auto-Start Algo-

rithm is reset. In the brake mode, all of the lower

DMOS drivers are ON, and the upper drivers are

OFF.

Note that Run/Brake should be brought low for a

period exceeding the value selected for the brake

delay time in order to initialize the brake delay cir-

cuit.

The Auto-Start Algorithm is based on an Align &

Go approach and can be visualized by referring to

Figure 9. Shown are the Output Enable and

Run/Brake control signals, sequencer output with

the resultant output phases, and the

Align and Go

status bits. The times labeled Tl and T2 are two

Figure 9: Auto Start Profile

Tasd <1>

Tasd <0>

Ta =T1

0.178 s

0.356 s

0.533 s

0.711 s

0.533 s

1.067 s

1.600 s

2.133 s

0.711 s

1.422 s

2.133 s

2.844 s

Note: PLL Reference Frequency = 90Hz

L6238

12/35

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