AA51883 Datasheet, PDF (5/7 Pages) Agamem Microelectronic Inc. – SERVO MOTOR CONTROLLER

AA51883 _{Agamem Microelectronics Inc.}
PRELIMINARY
SERVO MOTOR CONTROLLER
■ FUNCTIONAL DESCRIPTION
(1) Voltage Regulator
This circuit is composed of a band gap circuit, and outputs a 2.5-volt temperature
compensated reference voltage. This reference voltage is stabilized when the supply
voltage is variable.
(2) Saw tooth wave & One-Shot Generator
Connect a capacitor to CT pin will generate a triangular wave by constant current charging.
A typical value is 0.1uF. The constant current is determined by a resistor connected to RT
pin. A typical capacitor of approximately 0.1uF should be connected in parallel with the
resistor to increase stability.
(3) Servo Position & Over-Time logic
This circuitry consists of a pulse width comparator, which compares the servo position
detection signal (POT pin) from the one-shot timer (CT pin) whose period depends on the
resistance of a potentiometer connected to the servo's drive shaft. This feedback provides
the stability for the control circuitry.
(4) Pulse Stretcher
The difference between the servo control signal and the feedback signal is the error signal.
This error signal is used to toggle the direction of the current flows through the servo. The
function of this pulse stretcher is to “stretch” the small error signal long enough and
increases the duty cycle to the motor for it can maintain sufficient holding force. The circuit
also implements a “dead band” function that prevents servo jitter and hunting. This is a
range over which differences between the input and reference signals will not cause servo
operation. When the signal differences exceed this “dead band” range, the servo will start
to shift. The dead band will change according to the value of capacitor connected to the
C_DB pin.
(5) Directional Logic Control
The comparator circuit compares pulses from the servo control input (VIN pin) and the
voltage controlled pulse generator. It provides either a positive or a negative output
depending on whether the signal pulse width is larger or smaller than the position
generator’s output pulse (POT pin). Application of this error voltage to the motor driver
circuit causes the motor to turn in a direction that will minimize the error until both pulse
widths are the same.
(6) PWM Control
This signal generated by directional logic control block is used to control a flip-flop that
toggles the direction the current flows through the motor. The outputs of the flip-flop drive
©Copyright Agamem Microelectronics Inc.
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