Source of voltage transients

AN280

6/15

Doc ID 1703 Rev 3

Figure 3.

Parasitic wiring inductances in DC motor drive circuit

In fast switching applications, using the L6202, where the switching time is as short as 25

ns, the induced voltage spike can become quite large. For example if the DC motor in

Figure 3 was driven with 4 A and the bridge was switched off, a parasitic inductance of only

15 nH produces a 5 V spike. Since the current is reversed in both the supply and ground

leads the device can see a 10 V spike between the power supply pin and chip ground, if the

inductance of both wires are the same.

As a design example, consider a DC motor driver shown in Figure 1 with the following

system characteristics:

●

Supply voltage: max 46 V, min 38 V

●

Peak motor current: 5 A

●

Chopping frequency: 50 kHz

Figure 4.

Enable input and motor current for examples

For evaluation, the motor is driven with a peak current of 4 A. Figure 4 shows the input

signal for the L6202 on the Enable pin and the motor current used in the evaluation.

Here the bridge is energized and the load current is allowed to build up to 4 A. When the 4 A

peak is reached, the bridge is disabled and the current decays through the intrinsic diodes in

the DMOS power stage. All figures in the remainder of this note are taken under these

operating conditions.

AM15170v1

AM15171v1