CS3341 datasheet(4/6 Pages) CHERRY

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Application Information

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

Power Darlington

FIELD

R10

510Ω

STATOR

RECTIFIER

*C2

10µF

*Note: C2 optional for reduced jitter.

Figure 2. Typical Application Diagram

The CS3341 and CS3351 IC's are designed for use in an

alternator charging system. The circuit is also available in

flip-chip form as the CS387 and CS386.

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.

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 cur-

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

The ignition Terminal (I) switches power to the IC through

the VCC pin. In the CS3351/CS386, the Stator pin senses the

voltage from the stator. This will keep the device powered

while the voltage is high, and it also senses a stopped

engine condition and 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.

BATTERY

Lamp

Indicator

IGNITION

SWITCH

Regulator

Gnd

FIELD

FIELD Winding

STATOR

Winding

Figure 1. IAR System Block Diagram

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