L9918 datasheet(22/109 Pages) STMICROELECTRONICS

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3.2

PH characteristics

3.2.1

Alternator pole pairs

The selection of the correct alternator pole pairs is needed in order to make the device able to deduce the engine

rotation speed (RPM) from PH signal frequency (Hz):

RotationRPM =PHfreqHz*60

Npp

(1)

Where Npp is the alternator pole pairs number.

Possible selections for Npp are: 5, 6, 7, 8 and 9 (POLZ NVM bits).

3.2.2

Phase regulation

When the engine rotates and there is no alternator output current, the regulator has to recover a minimum voltage

on the stator coil in order to be ready for alternator rotation speed measurement.

When device detect that phase recovery is needed, EXC DC is no more driven by regulation loop logic but it

starts to be driven by Phase regulation function.

Starting of phase regulation function: the regulator monitors the phase voltage signal and checks if it oscillates

between two selected thresholds:

•

High threshold is selected depending on device state: if device is into Regulation state, high PH regulation

adopted threshold is VPHThREG,x, otherwise adopted threshold is VPHThSS,x. These two thresholds can be

programmed through KLV_NRSW and KLV_USSW NVM bits, respectively.

•

Low threshold value is VPLTh. Its value can be chosen between 1.8 and 2 V (KLV_LOWSW).VPLTh can be

either taken into account or ignored for PH regulation activation. This depends on KLV_HED_DIS NVM bit

programming.

In case one of these thresholds is not crossed by PH signal and B+ > set point (VBSPLINRG/VBSPDEF), Phase

regulation function is activated.

While phase regulation is active:

•

If B+ voltage is greater than set point voltage, EXC DC start from 25 % and increase by steps of 0.78 %

every regulation period. This raising transient continues up to a maximum value of 50 %.

•

If B+ voltage is smaller than set point voltage, EXC DC is determined by the regulation loop.

While Phase regulation is active, EXC signal behavior when B+ > VB+_LIM depends on OV_LIM_EN NVM bit.

When this is set to 0 and B+ > VB+_LIM, EXC DC is set to PWM_NRMAX (NVM bits).

When OV_LIM_EN is set to 1 and B+ > VB+_LIM, EXC DC is set to 0.

Phase regulation behavior respect to overvoltage function limit (U_FELD_AUS) can be selected through

LD_NR_DIS NVM bit.

While PH regulation function is active, LIN feedback on EXC DC can be chosen by DC_PHREG NVM bits.

3.2.3

Adaptive PH threshold calculation

L9918 is featured with an adaptive calculation system of PH signal threshold.

The aim of this system is to properly measure PH period and PH amplitude whatever the PH signal average value

is.

Picture below shows PH frequency calculation strategy using the adaptive PH thresholds.

L9918

PH characteristics

DS13000 - Rev 2

page 22/109

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