Dear people, it's me again, Mario:
for my bachelorthesis, there a still a few questions left about the operation of the LT8304. Those questions are mainly based on the block diagram from the datasheet. In the following picture, I roughly framed those parts of the diagram, which are still not clear:
Now to my six questions:
1. In the datasheet, the MOSFETs M2 and M3 are described as a sense circuit, but in the block diagram, there is a constant current source of 25µA on the left side. With a ratio of 1:4, it would try to hold the IRFB-current always at 100µA. So what is the real purpose of this circuit?
By the way, we use to call it “current mirror” in German.
2. Do the blocks A2 and gm work like simple comparators or do they have analog output values, dependent from the switch current (A2) or the voltage difference (gm)?
3. When does the block A3 reset and why it compares the output signals of A2 and gm?
4. How does the oscillator work and on which way it’s driven by the amplifier gm?
5. The datasheet gives an equation for the RFB-resistor:
Could you please tell me or give me a tip, how you came to this formula?
I tried to derive it by a mesh circulation, but I always came to an equation, dependent from the input voltage:
6. How does the temperature compensation (TC) work and what determines the PTAT voltage?
If you could give me an answer or notice to this questions, it would really help me!
I've got to submit my thesis 'till 31. August and the operation of the LT8304 ist the only topic, that's still a bit strange to me.
Thank you in advance!