EVAL6498L Bootstrap diode internal to the chip?

[Lello]

Hi there,

regarding EVAL6498L, is it necessary to mount the diode D1 (represented as not mounted in the schematic diagram)? or is D1 not necessary because the bootstrap supply diode is already included inside the 6498 integrated circuit?

Thank you

[Peter BENSCH · Accepted solution]

As a rule, the internal bootstrap circuit for supplying the high-side FET is sufficient and advantageous because the external diode with all its disadvantages can be saved.

However, there are cases where an external diode is useful - the AN1299 describes some of these in section 1. Don't be confused by the description L638xE tricks and tipps, at that time the L6498 did not yet exist, but the principle is the same.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

[Cristiana SCARAMEL]

Hello @Lello​,

I confirm the @Peter BENSCH​ info, in the L6498 an integrated structure can replaces the external diode even if it is slightly different from the one described in the AN1299 related to the L638x gate drivers family.

The bootstrap structure introduces a voltage drop (due to the internal DMOS). At low frequency this drop can be neglected, as the frequency increases, this should be taken into account.

If this drop is too high, or the circuit topology doesn’t allow a sufficient charging time, an external diode can be used.

In the datasheet - on page 12 and following - you can find a formula to estimate the voltage drop on the bootstrap DMOS.

[Lello]

Thank you Cristiana and Peter, it is really useful to know that that the L6498 has an internal bootstrap diode.

one additional question, just out of interest, is this gate driver fine to operate at frequencies up to 200 - 300KHz?

Thanks again

[Peter BENSCH]

Well, the datasheet says in section 3.3:

Maximum switching frequency at HVG, LVG load CL = 1 nF: 800kHz

Does it answer your question?

Regards

/Peter