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L9911

November 2005

This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice.

1

Features

2

Description

The L9911 is a monolithic multifunction alternator

voltage regulator intended for use in automotive

application. It includes the control section, the field

power stage, fault diagnostic circuit which drives a

warning lamp, and the protection against short cir-

cuits.

3

Circuit Operation

The alternator's voltage regulator performs the fol-

lowing main functions:

– 1) voltage regulation

– 2) protection

– 3) control fault diagnosis

– 4) load response control

3.1 VOLTAGE REGULATION

The alternator voltage is compared with a refer-

ence voltage in an amplifier, whose output deter-

mines the switching frequency of output power

MOS whose current excites the coil of the alterna-

tor; as the regulator is in fixed-frequency topology,

the field switching frequency does not depend on

the alternator characteristics. The regulators have

an integrated filter in the voltage sensing path

guaranteeing the correct behaviour of the devices

also when the rectifier diodes feature very high

switching spikes. The internal filtering allows the

usage of the device also with very long cables con-

necting the alternator to the battery with an imped-

ance so high to cause a superimposed ripple on

the alternator voltage higher than 5-6V. Conse-

quently it doesn't need, in the standard applica-

tion, any external component. Anyway an external

capacitor (2.2

µF) must be inserted between A+

and ground when using the device with very long

cables.

3.2 PROTECTION

It is present a protection against short circuits of

the lamp and the relay power drivers (L) and of the

field power driver (F+), a thermal drivers shutdown

protection and an overvoltage protection of L pow-

er drivers.

3.3 DIAGNOSIS

The circuit detects fault conditions related to the

phase and F+ status and receives informations

from one of the three alternator phases. In order to

prevent spurious indications, fault warnings are

not displayed immediately but are dalayed by a

fixed time.

3.4 LOAD RESPONSE CONTROL

The internal circuit regulates the soft start charac-

teristics (activated always at engine start) and the

soft attack characteristics.

PRELIMINARY DATA

CAR ALTERNATOR MULTIFUNCTION SMART VOLTAGE

REGULATOR

Rev. 3

Figure 1. Package

Table 1. Order Codes

Part Number

Package

Features

L9911A

Multiwatt8

See Table.9

L9911B

Multiwatt8

See Table.9

Multiwatt8