CS3361 Datasheet, PDF (4/5 Pages) Cherry Semiconductor Corporation – Alternator Voltage Regulator FET Driver

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.
STATOR
Winding
FIELD Winding
A
S
FIELD
Regulator
I
Lamp
Indicator
IGNITION
SWITCH
Gnd
BATTERY
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 V_CC 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.
Figure 1. IAR System Block Diagram
RECTIFIER
STATOR
S
R1
100kΩ
C3
.047µF
R2
R3
250Ω
*C2
10µF
C1
18kΩ
0.1µF R4
V_CC
STATOR _SC
Sense
50kΩ
OSC
Driver
R5
10kΩ
C4
0.022µF
IGN
LAMP
Gnd
R6
20kΩ
R7 ^10Ω
R9
2.4kΩ
A
D1
F
Q1
Logic level N
channel
enhancement
power FET
POWER
GROUND
I
Power
Darlington
FIELD
Lamp
Indicator
R10
510Ω
IGNITION
SWITCH
BATTERY
Figure 2. Typical Application Diagram
*Note: C2 optional for reduced jitter.
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