L8150 datasheet(29/37 Pages) STMICROELECTRONICS

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L8150

Precharge and hall effects filtering time description

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When the SD signal has a falling edge the logic acquires the Hall codification and waits for

next Hall effect commutation, which is filtered using a filtering time of TPRECHARGE =

400

µsec. The first significant zero-crossing signal is generated.

Also the second Hall effect commutation is filtered using TPRECHARGE, after that 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 right pattern, and the motor is able to

accelerate again.

Next filtering time used for the Hall commutation is a fraction of the elapsed time between

the last two zero-crossing signals TDzc. This filtering time is used until the first rising edge

on signal HallU is detected and a new zero-crossing signal is generated.

●

Let's consider a startup sequence forced by SD, supposing the motor rotating quickly in

the direction not imposed by the FR signal:

Figure 20.

Startup sequence forced by SD, supposing the motor rotating quickly in

the direction not imposed by the FR signal

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

signal high, which means all phases in high impedance state. Since the signal SD is high

and considering that this is the reset signal for the whole logic part, the system is not able to

detect if the motor is rotating in the desired direction or not and by default the DM signal will

be high. So when the signal SD has a falling edge, the DM signal remains high, indicating

that the detected direction is equal to desired direction.

Only after the first filtered Hall effect commutation the system is able to determines if the

rotation direction is equal to the desired one. At this moment the DM signal becomes low.

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

commutation, the logic outputs starts applying the right pattern, and the motor starts to

decelerate.

HALL BUS

FILTER TIME

PHASES

PHASES EXCITED

T∆zc

MOTOR DECELERATING

400 us

400 us T∆zc/576

MOTOR ACCELERATING

T∆zc/576

MOTOR FREE RUN

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