L8150 datasheet(27/37 Pages) STMICROELECTRONICS

27 / 37 page

L8150

Precharge and hall effects filtering time description

27/37

Figure 17.

Startup sequence forced by FS comparator, supposing the motor rotating

too quickly

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. If the motor is rotating too quickly the next Hall

effect commutation happens before the filtering time is elapsed: this causes the reset of the

filter and, in consequence, a new count for the filter time of 400

µsec. Until the motor is

rotating too quickly no Hall effect commutation is acquired by the logic, thus the logic outputs

force high impedance condition.

Only when the motor speed becomes lower than the speed necessary to obtain a

Tel/6>400

µsec the Hall effect commutations are filtered and acquired.

If no Hall effect commutation is acquired during a period of TelMax/6, a precharge function

will be done.

Depending on the last filtered Hall effect codification present in the logic and, also, on the

Hall effect codification having a duration longer than 400

µsec (because the Hall effect

codifications filtered have to be consecutive), the Hall effect commutations filtered using a

filter time of 400usec could be two or, more probably, three.

After this Hall effect commutations the logic outputs start applying the right pattern to the

motor windings.

The motor rotation direction is irrelevant, in fact this can influence only the kind of pattern

applied after the two or three filtered Hall effect commutation.

●

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

rotating slowly.

When the signal coming from the FS comparator has a falling edge, the logic waits for a Hall

effect commutation for a period of time equal to TelMAX/6. If no Hall effect commutation

happens during this time, the behaviour is the one described in the previous section, when a

startup sequence with motor stopped is described.

Let's suppose that during the counting period of TelMAX/6 a Hall effect commutation is

detected. This commutation is filtered using 400usec. Considering the hypothesis done,

starting from the Hall effect commutation detection, no more commutation will be detected

HALL BUS

FILTER TIME

PHASES

PHASES EXCITED

T∆zc’’/576

T∆zc’

Tel

MOTOR ROTATING TOO FAST

400 us

T∆zc’’

400 us

T∆zc’/576

T∆zc’

400 us

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