L8150 datasheet(22/37 Pages) STMICROELECTRONICS

22 / 37 page

Operating description

L8150

22/37

Figure 12.

Filter Block Diagram

The filter working principle is explained in the previous diagram (Figure 12): the main

component of the filter circuit is a 12-bit counter that is reset (to the value 0) whenever the

PosFil signal is equal to the Pos one. When the two signals are different (meaning that a

transition is happening), the counter will start counting as long as one of the following

conditions will occur:

●

Pos signal is again equal to former PosFil: in this case a noise is generating some Hall

comparator commutation,

●

the counter has reached or overcome the value set by Filter Length signal: in this case

the internal Hall signals will be latched into the PosFil register; immediately after this

event, PosFil will become equal to Pos and the counter will be reset.

At the same time (at the end of the filtering time), a flip-flop detecting the direction is

updated with the right direction information according to the former Hall decoding PosFil and

the new one Pos, immediately before latching it into the register.

12-bit Filter Length is set to two values according to different possibilities:

●

maximum filtering time, corresponding to 4096 clock periods (

≈420us in the typical

case, same used for pre-charge function) when an hall effect commutation is detected

just after a startup signal edge (SD or FS) and before TMAX/6 is elapsed. This filtering

time is also used when the motor accelerate starting from a stopped condition (no hall

effect commutation is detected from FS or SD edge to TMAX/6)

●

the filter length is a fraction of the elapsed time between two Zero Crossing signal (ZC).

During normal working (in case motor period is shorter than TMAX) it is equivalent to

0.625 electrical degrees.

A ZC signal is produced every time one of these situations happens:

●

a falling edge of the FS signal is detected

●

a rising edge of the HallU signal is detected

●

any hall effect commutations when the high impedance condition is forced by the IC

and the motor is in free-run condition

12 BIT

COUNTER

POS FIL

Pos

PosFil

Latch

Enable

Filter

Length

Reset

DELAY

1 Tclk

12 BIT

COUNTER

POS FIL

Pos

PosFil

Latch

Enable

Filter

Length

Reset

DELAY

1 Tclk

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