L8150 datasheet(25/37 Pages) STMICROELECTRONICS

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L8150

Precharge and hall effects filtering time description

25/37

Assumed this operation mode, it is easy to understand that as soon as the startup sequence

is over, Hall effects commutations are filtered using a fraction of the electrical period given

by the following equation, since T

∆ZC is equal to TEL when two consecutive zero-crossing

signals generated by a rising edge on signal HallU are detected:

●

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

rotating quickly in the direction imposed by the FR signal:

Figure 15.

Startup sequence forced by FS comparator, supposing the motor rotating

quickly in the direction imposed by the FR signal:

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

crossing signal is generated and 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, after that the second

zero-crossing signal is generated.

Starting from 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.

The next filtering time used for the Hall commutation 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.

●

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

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

FILTER

ROATING

–

576

---------- T

∆

576

---------- T

⋅

HALL BUS

FILTER TIME

PHASES

PHASES EXCITED

T∆zc’’/576

T∆zc’

Tel

MOTOR ACCELERATING

400 us

T∆zc’’

T∆zc’/576

T∆zc’’/576

400 us

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