CS3361

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6

APPLICATIONS INFORMATION

The CS3361 is designed for use in an alternator charging

system.

In a standard alternator design (Figure 3), the rotor carries

the field winding. An alternator rotor usually has several N

and S poles. The magnetic field for the rotor is produced by

forcing current through a field or rotor winding. The Stator

windings are formed into a number of coils spaced around

a cylindrical core. The number of coils equals the number of

pairs of N and S poles on the rotor. The alternating current

in the Stator windings is rectified by the diodes and applied

to the regulator. By controlling the amount of field current,

the magnetic field strength is controlled and hence the

output voltage of the alternator.

Referring to Figure 7, a typical application diagram, the

oscillator frequency is set by an external capacitor

connected between OSC and ground. The sawtooth

waveform ramps between 1.0 V and 3.0 V and provides the

timing for the system. For the circuit shown the oscillator

frequency is approximately 140 Hz. The alternator voltage

is sensed at Terminal A via the resistor divider network

R1/R2 on the Sense pin of the IC. The voltage at the sense

pin determines the duty cycle for the regulator. The voltage

is adjusted by potentiometer R2. A relatively low voltage on

the sense pin causes a long duty cycle that increases the Field

current. A high voltage results in a short duty cycle.

The ignition Terminal (I) switches power to the IC

from the stator and senses a stopped engine condition. It

drives the Lamp pin high after the stator timeout expires.

The Lamp pin also goes high when an overvoltage condition

is detected on the sense pin. This causes the darlington lamp

drive transistor to switch on and pull current through the

lamp. If the system voltage continues to increase, the field

and lamp output turn off as in an overvoltage or load dump

condition.

The SC or Short Circuit pin monitors the field voltage. If

the drive output and the SC voltage are simultaneously high

for a predetermined period, a short circuit condition is

assumed and the output is disabled. The regulator is forced

to a minimum short circuit duty cycle.

Figure 3. IAR System Block Diagram

BATT

IGNITION

SWITCH

Regulator

A

GND

I

S

FIELD

FIELD

Winding

STATOR

Winding

Lamp

Indicator