ca3228 Harris Corporation, ca3228 Datasheet - Page 6

• Manufacturer Part Number: ca3228
• Description: Speed Control System With Memory
• Manufacturer: Harris Corporation

Device Description and Operation
The functional block diagram and Figures 1, 2 show the
speed- control flow chart, and a typical automotive speed-
control application, respectively.
Command Decoder and Delay Logics (Pins 3,4)
Driver commands are input to pin 3 through the Driver
Command Line. These signals are encoded on a single line
as voltage levels selected by switches which adjust a resistor
divider network.
The voltage level established is compared to a reference
level which decodes the command. A command level greater
than V
control. Once the system is enabled, a voltage level of
0.88V
ACCEL, and COAST command, respectively. A driver
command of 0.12V
The Driver Command Delay established by the current
sources and a capacitor at pin 4 assures that ON, OFF,
ACCEL, and COAST commands are considered valid only if
longer than 50ms. The time for RESUME is 330ms.
Control Logic
The Control Logic accepts signals from the command
decoder and other sensors. It causes the memory to be
updated when operating in ACCEL and COAST modes. It
will put the system in Standby mode if brakes are applied, if
the speed error exceeds 11mph, or if the vehicle speed
drops below the minimum Speed Lockout (25mph). It will
return the vehicle to the previous set memory speed when a
RESUME command is given.
Frequency to Voltage Converter (Pins 8-11)
The speed sensor input f
frequency is directly proportional to the vehicle speed at
approximately 2.22Hz/mph The current sources, capacitor
and comparators at pin 9 cause equal rise and fall times to
occur at pin 9 on the positive- and negative-going slopes of
the sensor input. Pulse currents of time duration equal to the
rise and fall times are used to charge the parallel resistor
capacitor combination at pin 10 to give a voltage (V
10 proportional to frequency at approximately 27mV/Hz. The
f
the filter capacitors at pins 8 and 9. However, the maximum-
to-minimum frequency ratio will remain fixed.
S
FIGURE 4. TYPICAL D/A MEMORY VOLTAGE, V
frequency range may be altered by changing the values of
CC
CC
, 0.66V
+ 0.8V turns the system On, enabling dynamic
6
5
4
3
2
1
0
CC
0
, and 0.38V
CC
or less turns the system Off.
x
x
x
50
FREQUENCY, f
S
at pin 8 is an AC signal whose
100
CC
+25
decodes the RESUME,
150
o
S
C
-40
(Hz)
o
C
200
+85
M
o
C
vs
S
) at pin
CA3228
10-36
Memory Voltage, V
Upon release of the ACCEL or COAST switches the voltage,
representing vehicle speed V
from the frequency-to-voltage converter, is stored as a
binary number in a 9 bit counter. A memory update compar-
ator allows clocking of the counter until memory voltage V
equals V
network which provides memory voltage V
Analog Accelerate and Resume Generator (Pins 14,15)
Numerous functions are combined in what is called the
Analog Accelerate and Resume Generator. The circuit
switches the signal output at pin 15 depending on the mode
of operation. In the Accelerate and Resume mode the
capacitor at pin 15 is charged at a fixed rate [450mV/(R
(C
voltage (V
Minimum Speed Lockout, and Coast modes, pin 15 follows
the voltage representing vehicle speed (V
Error Amplifier (Pin 16)
In the Cruise mode the Error Amplifier determines the
difference between the set memory speed (V
actual speed (V
amplifier where it defines whether VAC or VENT is required.
The error signal represents deviation in vehicle speed from
the memory or set speed condition. The Error signal is also
used to control the Redundant Brake feature.
Redundant Brake Comparator
When the error output drops below approximately 0.42V
the Redundant Brake output is activated. Redundant Brake
causes the chip to go into the Standby mode.
Control Amplifier (Pins 18, 20)
The Control Amplifier is an op amp using external
components to set the gain. Inputs to the Control Amplifier
are from the Error Amplifier output, servo position sensor
and align output. The output of the Control Amplifier controls
the VAC and VENT outputs.
VAC, VENT and Gate-Driver Outputs (Pins 21, 22, 23)
The VAC, VENT and Gate Outputs are open collector
devices used to control the throttle position. For the system
FIGURE 5. TYPICAL CHARACTERISTIC F/V CONVERTER
EXT
)]. In the Cruise mode pin 15 follows the memory
S
M
. The output of the counter controls a ladder
) and in the On, Off, Brake, Redundant Brake,
FREQUENCY
OUTPUT, V
6
5
4
3
2
1
0
0
S
). This error signal is fed to the control
M
50
(Pin 6)
S
FREQUENCY, f
-40
vs FREQUENCY
o
C
100
S
+25
determined by the output
150
S
o
C
(Hz)
-40
S
o
M
C
).
200
at pin 6.
+85
o
M
C
250
) and the
EXT
CC
M
)
,