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
Figure 1. IAR System Block Diagram
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.
VCC STATOR SC
Figure 2. Typical Application Diagram
*Note: C2 optional for reduced jitter.