CS3361 datasheet(4/5 Pages) CHERRY

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Application Information

The CS3361 is designed for use in an alternator charging

system.

In a standard alternator design (Figure 1), 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 cur-

rent 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.

Figure 1. IAR System Block Diagram

Referring to Figure 2, a typical application diagram, the

oscillator frequency is set by an external capacitor connect-

ed between OSC and ground. The sawtooth waveform

ramps between 1V and 3V and provides the timing for the

system. For the circuit shown the oscillator frequency is

approximately 140Hz. 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 through

the VCC pin. The Stator pin monitors the voltage 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 detect-

ed 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.

BATTERY

Lamp

Indicator

IGNITION

SWITCH

Regulator

Gnd

FIELD

FIELD Winding

STATOR

Winding

Figure 2. Typical Application Diagram

10kΩ

Driver

Gnd

STATOR

Sense

VCC

OSC

IGN

20kΩ

0.022µF

50kΩ

.047µF

100kΩ

250Ω

0.1µF

18kΩ

BATTERY

LAMP

2.4kΩ

10Ω

Power

Darlington

Lamp

Indicator

IGNITION

SWITCH

POWER

GROUND

Logic level N

channel

enhancement

power FET

FIELD

R10

510Ω

STATOR

RECTIFIER

*C2

10µF

*Note: C2 optional for reduced jitter.

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