L9912 datasheet(66/84 Pages) STMICROELECTRONICS

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SPI interface

L9912

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DocID029639 Rev 2

13.4.7

PH-SENSE register [0x13]

L9912 system provides a Phase Period Measurement block: the input phase signal (or

signals) is (are) suitably filtered and processed.

The logic measures the time interval (PhaseMeas), in 64 us units, corresponding to 4

periods (PhasePeriod = PhaseMeas / 4) of the phase signal: this time can be easily

converted into the rotor speed according to the number of pole pairs (Np):

RotorSpeed (rpm) =

For example, at 3000 rpm, in a system with 6 pole pairs, we obtain the following data:

Therefore, reading the 208 value and applying the above formula we can compute:

Table 47. PH-SENSE register [0x13]

Bit

Reset

value

Description

PH-Sense Measurement Timed -

OUT

This bit indicates the absence of rotation or a

too slow rotation

The timeout is notified to the microcontroller by

setting bit 0 of GSW word.

The flag is cleared by reading this register

PHASE_REGULATION_REQUEST

This bit, valid only when a new phase value has

been notified (GSW.0=1) indicates that the

phase input voltage has been below the

threshold for at least 4 periods.

Reserved

10-0 RPM_PHASE_PERIOD

This register contains the phase sense

measurement expressed into 64 us units.

A new available measurement or is notified to

the microcontroller by setting bit 0 of GSW

word.

The new measurement notification is cleared by

reading this register

Table 48. Example in a system with 6 pole pairs at 3000 rpm

Parameter

Value

Rotor frequency

50 Hz (3000 rpm / 60)

Phase frequency

300 Hz (50 * 6)

Phase period

3.33 ms

4 phase periods

13.33 ms

Phase measurement

208 (13.33 ms / 64 µs)

Np PhasePeriod



--------------------------------------------------

PhaseMeas:4





---------------------------------------------------------

240

Np PhaseMeas



-----------------------------------------------

240

Np PhaseVal 64

s



-----------------------------------------------------------

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