TPS62750: TPS62750 - average input current limit

Dear Chris,

Many thanks for your response!

So, for the case shown in Fig. 16, the DC/DC converter does not operate in PWM? In such a case, then Iin is equal to Icoil?

By the way, do you know how the input current is measured? According to the block diagram shown in p.5 it seems that the input current is measured through the voltage drop across the high-side MOSFET, is that right?

Many thanks, again!

Ferran

I don't understand the first part of your question.

The IC measures the input current in the high side FET.

But Figure 16 is measuring the input current to the circuit (before the input cap) with a current probe.

Dear Chris,

Thanks again for your response!

I believe that my misunderstanding was in “what is Iin”. I thought that it was the input current after the input capacitor, not before. If the input current after the input capacitor was represented in Fig. 16, I suppose that we would see the transitions to zero commonly expected in PWM, right?

Many thanks, again!

Ferran

Yes, this current would be peaks with 0 currents in between.

Dear Chris,

I have another question with regard to the average input current limit of the TPS62750.

Taking into account that such a current is averaged, I suppose that there is a transient when the current limit is changed (for instance, from 100 mA to 300 mA). Do you know how long is this transient, assuming that the DC/DC converter is always enabled?

Many thanks, again!

Ferran

This is not specified, so the performance would need to be verified as ok for your specific application.

Dear Chris,

I have another question. The high-side mosfet of the TPS62750 is represented as an NMOS transistor in the functional block diagram of the datasheet, but I thought that this transistor was generally a pmos device. Is there any error in such a block diagram?

Many thanks, again!

Ferran

There are techniques in the IC design to use either NMOS or PMOS. It doesn't really matter from the outside.

But for the TPS62750, is it really an NMOS transistor employed for the high-side mosfet?

Many thanks!

Why does this matter for your design? Perhaps there is a different question at root here.

Details like this are generally proprietary.