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SAA1042 View Datasheet(PDF) - Motorola => Freescale

Part Name
Description
View to exact match
SAA1042
Motorola
Motorola => Freescale Motorola
SAA1042 Datasheet PDF : 6 Pages
1 2 3 4 5 6
SAA1042
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, as shown
in Figure 1.
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
VF = (see Figure 4)
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
Figure 2 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. Figure 7 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. Figure 6 shows the Timing Diagram.
Figure 7 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 kis
chosen according to Figure 2.
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, (see Figure 6).
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.
The total power dissipation of the circuit can be
determined from Figures 3 and 5:
PD = 0.9 W + 0.08 W = 0.98 W.
The junction temperature can then be computed using
Figure 8.
MOTOROLA ANALOG IC DEVICE DATA
3
 

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