L8150 datasheet(26/37 Pages) STMICROELECTRONICS

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Precharge and hall effects filtering time description

L8150

26/37

Figure 16.

Startup sequence forced by FS comparator, supposing the motor rotating

quickly in the direction opposite to that imposed by the FR signal

This situation is similar to the one described before, except DM behaviour. Let's suppose the

FS signal high, which means all phases in high impedance state. Even if the signal FS is

high, the logic is able to detect if the motor is rotating in the desired direction or not. So

when the signal coming from the FS comparator has a falling edge, by default a zero-

crossing signal is generated and the DM signal is already low, indicating that the detected

direction is not equal to desired direction.

From now on the logic waits for a Hall effect commutation and applies to it a filtering time of

TPRECHARGE=400µsec. The first significant zero-crossing signal is generated.

Also the second Hall effect commutation is filtered using TPRECHARGE, and the second zero-

crossing signal is generated.

Starting form the second Hall effect commutation, after the acquisition of the filtered Hall

commutation, the logic outputs start applying the rectangular pattern, and the motor is able

to decelerate until the rotation direction changes becoming equal to the desired one.

After the first two Hall commutations, the filtering time used is a fraction of the elapsed time

between the first two Hall effect commutations, according to the previous TFILTER equation.

This filtering time is used until the first rising edge on signal HallU is detected and a zero-

crossing signal is generated. After that the filtering time used is a fraction of the elapsed

time between the last two detected zero-crossing signals, in other words between the

second Hall effect commutation and the rising edge on signal HallU. Finally, when the

second rising edge on signal HallU is detected, the filtering time used is a fraction of the

electrical period, as described in previous TFILTER-ROTATING equation.

Only when a Hall effect commutation consistent with the desired direction is detected the

DM signal becomes high, indicating the right direction detection.

●

Let's consider a startup sequence forced by FS comparator, supposing the motor

rotating too quickly:

HALL BUS

FILTER TIME

PHASES

PHASES EXCITED

T∆zc’

MOTOR DECELERATING

400 us

T∆zc’/576

MOTOR ACCELERATING

T∆zc’/576

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