Approach to the study

AN2842

8/22

Doc ID 15110 Rev 1

With the Q1 device in position A and Q2 in position B, the current relative to Q1 (yellow line)

changes depending on its position, and in particular, during turn-on detail it is bigger than

Q2. When Q1 is put in position B and Q2 in A, its current is lower than Q2. So, the device

behaviors are linked to their positions. In this case it is necessary to compensate this

difference or redesign the circuit to reduce the PCB differences. A deeper analysis has

shown a small difference in the source path, a difference that caused unbalanced current

during turn-on operation and then different working temperatures (if the devices are

mounted on different heat-sinks). If the system arrives at a thermal balance, different

working temperatures for the devices are the final results. Instead, when the circuit has very

similar parameters in terms of electrical characteristics as the devices, layout considerations

and so on, the currents and the relative waveforms are balanced as shown in

Figure 8.

Figure 8.

Details of current balance when circuit has very similar parameters

In the switching system, as seen previously, when the current imbalance is due principally at

the voltage on the gate circuitry, main different happens not clear during the commutation; in

fact, during this phase the variation between branches causes different voltage on the gate

pin. If we look at the

Figure 9 and Figure 10, we can see the details during the switching on

in two different conditions.