L8150 datasheet(30/37 Pages) STMICROELECTRONICS

30 / 37 page

Precharge and hall effects filtering time description

L8150

30/37

Only when an 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 SD signal, supposing the motor rotating

too quickly:

Figure 21.

Startup sequence forced by SD signal, supposing the motor rotating too

quickly

When the SD signal has a falling edge the logic waits for an Hall effect commutation. If the

motor is rotating too quickly the next Hall effect commutation occurs before the filtering time

has elapsed.

This means that a new Hall filter count is performed and no Hall effect codification is

acquired until TPRECHARGE has elapsed while the Hall bus is not changed.

Until the motor rotates 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 commutation are filtered and acquired.

After the first two or three filtered Hall effect commutations (because they have to be

consecutive), the logic outputs start applying the right pattern to the motor windings.

The motor rotation direction is not important, in fact this can influence only the kind of

pattern applied after the two or three filtered Hall effect commutation. In the picture is

reported the less likely situation.

●

Let's consider a startup sequence forced by SD, supposing the motor rotating slowly.

When the signal coming from the SD-Comparator has a falling edge, the logic waits for an

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

occurs during this time, the behaviour is that 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 an Hall effect commutation is

detected. This commutation is filtered using 400

µsec. Considering the hypothesis done,

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

for the following TelMAX/6 and the behaviour is the one described in the startup sequence

with motor stopped.

HALL BUS

FILTER TIME

PHASES

PHASES EXCITED

T∆zc’’/576

T∆zc’

Tel

MOTOR ROTATING TOO FAST

T∆zc’’

400 us

T∆zc’/576

400 us

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