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AN469 APPLICATION NOTE

one of the lower transistors of the bridge for bipolar motors. Both of these implementations produce a low ripple

current since the voltage across the motor during the recirculation time is much less than the power supply volt-

age. Figure 4 shows the ripple current for bipolar motor applications using the L6506 and the L298N.

Figure 3. Input Signal for Stepper Motor Drive.

When implementing a half step drive, both outputs of the L6506 will be low during the half step of one phase.

This means a very long time is required for the current in the "off" winding to decay when driving bipolar motors.

Alternately, the power stage (L298N) may be inhibited to put the output in the state and achieve a faster current

decay. Since separate Vref inputs are provided for each channel, each of the loads may be programmed inde-

pendently allowing the device to be used to implement microstepping or applications with different peak and

hold currents. In this type of application, changing the reference voltage (Vref) will change the load current, ef-

fectively implementing a transconductance amplifier.

SYNCHRONIZING MULTIPLE DEVICES

Ground noise problems in multiple configurations can be avoided by synchronizing the oscillators. This may be

done by connecting the sync pins of each of the devices with the oscillator output of the master device and con-

necting the R/C pin of the unused oscillators to ground as shown in figure 5.

The devices may be synchronized to external circuits by applying synchronizing pulses to the sync pins. It

should be noted, however, that the input pulse sets the minimum on time of the outputs and will therefore set a

minimum output average current.

Figure 4. Ripple Current in Bipolar Motors.

Figure 5. Synchronizing Multiple Devices.