(ADuM4120)How fast can ADuM4120 move?

Hello Kawa,

There isn't an exact maximum frequency that the ADuM4120 can work at, but there are some limitations:

1) There is a minimum pulse width. This applies to both the on and off portions of the cycle.

2) Higher frequency operation will have more internal heating due to power dissipation within the ADuM4120.

The power dissipation is usually the main factor in maximum switching frequency. The simplified equation for this is:

Power dissipation in ADuM4120 = [Rint / (Rext+Rint) ] * Qtot * Vgate * Fs + Iquiescent * Vgate

Rint is the internal Rdson of the gate driver

Rext is the external series gate resistor

Qtot is the total gate charge of the switch being driven

Vgate is the voltage the gate is driven to

Fs is the switching frequency

Iquiescent  is the quiescent current of the gate driver

The power dissipation has to be kept lower than the amount that would make the part rise to 125ºC. Using either Theta-Ja or Psi-Jc, you can know how much thermal headroom there is based on ambient or case temperatures.

I've run the ADuM4120 well above 1 MHz, but only in a lab setup at room temperature with a small load. It is important to have a lot of extra thermal headroom in an actual application, as the ambient temperature in real applications can often fluctuate, or be uneven.

RSchnell