The SAA1042 drives a two–phase stepper motor in the bipolar mode. The device contains three input stages, a logic section and two output stages. The IC is contained in a 16 pin dual–in–line heat tab plastic package for improved heatsinking capability. The center four ground pins are connected to the copper alloy heat tab and improve thermal conduction from the die to the circuit board.
• Drive Stages Designed for Motors: 6.0 V and 12 V: SAA1042V
• 500 mA/Coil Drive Capability
• Built–In Clamp Diodes for Overvoltage Suppression
• Wide Logic Supply Voltage Range
• Accepts Commands for CW/CCW and Half/Full Step Operation
• Inputs Compatible with Popular Logic Families: MOS, TTL, DTL
• Set Input Defined Output State
• Drive Stage Bias Adaptable to Motor Power Dissipation for Optimum Efficiency
INPUT/OUTPUT FUNCTIONS
Clock — (Pin 7) This input is active on the positive edge of the clock pulse and accepts Logic ‘1’ input levels dependent on the supply voltage and includes hysteresis for noise
immunity. CW/CCW — (Pin 10) This input determines the motor’s rotational direction. When the input is held low, (OV, see the electrical characteristics) the motor’s direction is nominally clockwise (CW). When the input is in the high state, Logic ‘1’, the motor direction is nominally counter clockwise (CCW),depending on the motor connections.
Full/Half Step — (Pin 8) This input determines the angular rotation of the motor for each clock pulse. In the low state, the motor will make a full step for each applied clock pulse, while in the high state, the motor will make half a step.
VD — (Pin 2) This pin is used to protect the outputs (1, 3,14,16) where large positive spikes occur due to switching the motor coils. The maximum allowable voltage on these pins is
the clamp voltage (Vclamp). Motor performance is improved if a zener diode is connected between Pin 2 and 15. The following conditions have to be considered when selecting the zener diode:
Vclamp = VM + 6.0 v
VZ = Vclamp - VM - VF
where: VF = clamp diodes forward voltage drop
Vclamp: <= 20 V for SAA1042V <= 30 V for
Vclamp: SAA1042AV
Pins 2 and 15 can be linked, in this case VZ = 0 V.
Set/Bias Input — (Pin 6) This input has two functions:
1) The resistor RB adapts the drivers to the motor current.
2) A pulse via the resistor RB sets the outputs (1, 3, 14, 16) to
a defined state.
The resistor RB can be determined from the graph of according to the motor current and voltage. Smaller values of RB will increase the power dissipation of the circuit
and larger values of RB may increase the saturation voltage of the driver transistors. When the “set” function is not used, terminal A of the resistor RB must be grounded. When the set function is used, terminal A has to be connected to an open–collector (buffer) circuit. shows this configuration. The buffer circuit (off–state) has to sustain the motor voltage (VM). When a pulse is applied via the buffer and the bias resistor (RB), the motor driver transistors are turned off during the pulse and after the pulse has ended, the outputs will be in defined
states. shows the Timing Diagram. illustrates a typical application in which the SAA1042 drives a 12 V stepper motor with a current consumption of 200 mA/coil. A bias resistor (RB) of 56 kW is the maximum voltage permitted at the output pin is VM + 6.0 V (see Maximum Ratings table), in this application VM = 12 V, therefore the maximum voltage is 18 V. The
outputs are protected by the internal diodes and an external zener connected between Pins 2 and 15. From Figure 4, it can be seen that the voltage drop across the internal diodes is about 1.7 V at 200 mA. This results in a zener voltage between Pins 2 and 15 of:
VZ = 6.0 V – 1.7 V = 4.3 V.
To allow for production tolerances and a safety margin, a 3.9 V zener has been chosen for this example. The clock is derived from the line frequency which is phase–locked by the MC14046B and the MC14024. The voltage on the clock input is normally low (Logic ‘0’). The motor steps on the positive going transition of the clock pulse. The Logic ‘0’ applied to the Full/Half input (Pin 8) operates the motor in Full Step mode. A Logic ‘1’ at this input will result in Half Step mode. The logic level state on the CW/CCW input (Pin 10), and the connection of the motor coils to the outputs determines the rotational direction of the motor. These two inputs should be biased to a Logic ‘0’ or ‘1’ and not left floating. In the event of non–use, they should be tied to ground or the logic supply line, VCC. The output drivers can be set to a fixed operating point by use of the Set input and a bias resistor, RB. A positive pulse to this input turns the drivers off and sets the logic state of the outputs. After the negative going transition of the Set pulse, and until the first positive going transition of the clock, the outputs will be:
L1 = L3 = high and L2 = L4 = low
The Set input can be driven by a MC14007B or a transistor whose collector resistor is RB. If the input is not used, the bottom of RB must be grounded.
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