L9918 datasheet(4/109 Pages) STMICROELECTRONICS

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1.3.2

Closed loop voltage control

L9918 regulates the voltage on car loads by closed loop control. Target voltage (set point) can be chosen by

default (UR_DEF_REG NVM bits) or it can be sent by the Engine Control Unit (ECU) through LIN interface

(VBSPLINRG).

1.3.3

Load response control (LRC)

The torque applied to the engine by the alternator is proportional to the alternator output current. If an electrical

load is applied by vehicle harness, the torque applied to the engine can be too high to be sustained, especially if

engine is running at low RPM. The LRC is intended to manage temporarily the alternator output current variation

in order to limit torque demand variation.

On high rotational speeds, engines do not suffer from torque changes. For this reason load response is switched

off for RPM > SPLRC,x such that any DC adjustment is executed immediately. The load response function will be

active again if RPM < SPLRC,x condition is detected.

The LRC can be configured by ECU via LIN or it can adopt a default configuration (NVM programming).

To avoid permanent voltage adjustment with load response control (while RPM < SPLRC,x), even in case of small

duty cycle variations, the regulator has a "blind-zone" range. If duty cycle variation falls within this range, LRC is

not activated. Blind zone control can be programmed by TV_SPRUNG NVM bits.

The blind zone can be switched through LIN RX frame. This feature can be enabled or disabled by programming

TV_SPRUNG_EN NVM bit. In case the feature is disabled (TV_SPRUNG_EN = 0) the regulator applies a

programmed default value: blind zone can’t be changed via LIN and commands corresponding to BZ change into

the RX frames are ignored.

1.3.4

Pre-excitation

Conditions for pre-excitation are defined in the internal state machine. In pre-excitation mode, the rotor is

magnetized with a fixed duty cycle in order to produce an induced voltage as soon as the engine turns on.

Device behavior in pre-excitation is highly configurable. More detailed explanation on all the possible pre-

excitation modes are provided in Section 4.2.3 Pre-excitation specific mode selection

1.3.5

Phase regulation

When the engine rotates and the device is regulating, the regulator requires a minimum voltage level on the stator

coil signal (phase signal) in order to be ready for engine rotation speed measurement. Proper phase signal level

is guaranteed by phase regulation function (Section 3.2.2 Phase regulation).

1.3.6

Low voltage function

When very low battery voltage is measured, current provided to the excitation coil is driven forcing excitation duty

cycle at 100% until a minimum defined voltage is achieved (Section 2.2.4 UV/OV management).

1.3.7

Overvoltage safety function

L9918 implements an EXC switch off safety function in case of overvoltage detection (Section 2.2.4 UV/OV

management).

1.3.8

Overvoltage function

Other than Overvoltage safety function, L9918 is equipped with a further overvoltage function, which allows filter

time and threshold programmability (Section 2.2.4 UV/OV management).

1.3.9

Excitation current measurements

Device is equipped with a current sensor in order to measure the current flowing out from EXC pin

(Section 4.2.6 Excitation current measurement).

1.3.10

Current limitation and overcurrent protection

Current limitation can be used to limit the EXC current. Current limitation activation threshold can be set by LIN or

by specific NVM bits programming.

L9918

List of device features

DS13000 - Rev 2

page 4/109

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