CS3341/3351/386/387
Application Information
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 V
CC
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.
A
Regulator
S
I
Lamp
Indicator
STATOR
Winding
IGNITION
SWITCH
FIELD
Gnd
BATTERY
FIELD Winding
Figure 1. IAR System Block Diagram
RECTIFIER
STATOR
S
A
R3
250Ω
R1
100kΩ
*
C2
10µF
V
CC
Sense
C1
0.1µF
18kΩ
R4
SC
R5 10kΩ
D1
STATOR
F
C3
.047µF
Driver
Q1
Power Darlington
LAMP
Gnd
FIELD
R2
50kΩ
OSC
IGN
C4
0.022µF
R6
20kΩ
R9
2.4kΩ
R10
510Ω
POWER GROUND
I
Lamp
Indicator
R7
10Ω
IGNITION
SWITCH
Power
Darlington
BATTERY
*
Note: C2 optional for reduced jitter.
Figure 2. Typical Application Diagram
4
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
