Device description

L9409

6/13

Doc ID 022665 Rev 2

4

Device description

4.1

Voltage regulation

4.1.1

Description

The alternator voltage is compared with a reference voltage in an amplifier. This device

senses the battery voltage in two ways: the B+ pin and the S pin. The last could be left

S pin is used. This second condition assures a better knowledge of the real value of the

battery voltage if a direct connection with the positive terminal of the battery is made as

shown in Figure 1. The field driver works at a fixed frequency. A variable duty cycle is applied

on the field winding according with the error between the voltage set-point and the

measured battery voltage. The voltage set-point depends on case temperature. A set-point

voltage vs. case temperature curve is integrated in the device and is shown in Figure 3.

4.1.2

Electrical characteristic

Table 6.

Electrical characteristics

Symbol

Parameter

Test condition

Min.

Typ.

Max.

Unit

Standby current

-

-

400

µA

Regulation set-point voltage

@ 25 °C

-

14.5

-

V

Initiation of regulation detection

-

1.5

-

V

Pre-excitation

-

19

-

25

%

Initiation of field regulation

frequency

-

360

400

440

Hz

Thermal compensation

-40 °C

 T

-0.5

0

0.5

mV/°C

-10 °C

 T

-8

-10

-12

mV/°C

100 °C

 T

-0.5

0

0.5

mV/°C

Load regulation

18000 rpm, 10% to 90% load

-

-

200

mV

Speed regulation

Guarantee by design

-

-

200

mV

Field driver on resistance

-

-

130

m



Field limit current

F shorted to GND @ -40 °C

8

-

15

A

F shorted to GND @ 25 °C

8

-

15

A

F shorted to GND @ 150 °C

7.5

-

14.5

A

Field discharge rectifier

-

-

1.85

V

Diode reverse current

-

-

-

20

µA

Pull down current on P terminal -

0.4

-

1.4

mA

1.