Driving low impedance load at high frequency with MOSFET continuation

[sonnytiger]

Okay, but if the pin is floating, isn't it at 0V? which would be higher than -0.3234234345345V? Or is floating "undefined"?

[c4757p]

Floating is definitely "undefined". A floating pin is at the mercy of whatever bias currents are applied to it and whatever EMI happens to be in its general area. That's why you never leave unused CMOS inputs (on logic gates, etc) floating, flapping in the EMI breeze.

[sonnytiger]

Hahaha nice gotcha, oh and one more thing it specifies that the maximum input voltage is 1V, If i take 2 base emitter junctions in series, measured as 1.3V, this would result in a peak of 1.4V or something like that, making the output turn on for some period of time then off. Is this an issue or should I just go for it and see what happens?

[c4757p]

Stick a resistor on it. IIRC it has a clamp diode in there (not shown on the datasheet) that will take a lot of current if unrestricted.

The "proper" answer is "never exceed the absolute maximums". The proper answer is that for hobby stuff, who gives a crap if you're not blowing the ass out of the chip? Voltage maximums can often be exceeded by just a little bit if you limit the current in case something is unhappy.

[sonnytiger]

Okay, well I did it with a 10k in series with the two transistors and on the scope i see very small ramp starting at like 1.5V going to 2V on pin 3. And I see no output at all. Just at ground level. Another thing is the ramp from Rt/Ct will always be more than the inverted input, so how would that work in the first place?

[c4757p]

Okay, well I did it with a 10k in series with the two transistors and on the scope i see very small ramp starting at like 1.5V going to 2V on pin 3. And I see no output at all. Just at ground level. Another thing is the ramp from Rt/Ct will always be more than the inverted input, so how would that work in the first place?

How exactly do you have this connected? The purpose of the diodes is to subtract their voltage drop from Rt/Ct so that it's not more than the threshold any more.

[sonnytiger]

I hat two transistor connected base to emitter with a 10k resister all in series going from the Rt/Ct pin to Current Sense, with the base connected to Rt/Ct. I just realized that the output should turn on when the latch is set rather than reset, but it doesn't am I missing something here? What is the block with the T in it and the triangle on the input?

[c4757p]

T latch. (Latch, not flip-flop, so just ignore the clock input in the article.)

[sonnytiger]

Sigh, I am really having trouble under standing the Current sense input. If the comparator will output HIGH when the current sense input is higher than the other input, should it be higher at all times no matter what? even if i subtracted all the voltage away, it will still be higher. I don't understand at all. Grrrrrr