1) For open collector / open drain comparators, is there something like a minimum current limit? Usually the pull up resistors in the datasheets are rather low values, geared more towards the maximum allowed sink current. Understandably. But if the load I want to drive is like a cmos and I only need a very few uAmps, are there any problems to be anticipated when the sink current is really low due to a very high value pull up resistor?
Min would be leakage considerations, which could affect noise margin, logic levels, if Rpullup and/or leakage too high.
2) Differential input voltage. This one really scares me, but maybe I get it wrong.
Usually the common mode input (I presume that referes to the max. voltage I can safely apply to either the inverting or noninverting input? Still fighting that common mode terminus) is around or slightly below the supply voltage. Some notable exceptions, like the LT1116, allow input voltages to be massively above the positive supply voltage, but those are rather scarce.
So I assumed the invertig and the noninvering outputs may as well be on either side of the supply voltage, so if I had ±12V supply, I could have a reference of -11V @ the inverting and +11V @ the non inverting input. Would make for a 22V difference. But that is not automatically to be implied?
If a differential voltage of 5V is given, then I could only apply -6V to the non inverting input in above example? Is the differential voltage an additional input restriction? Or am I completely off track?
Because the AD790 specifies common mode as +VS -2V, while the differential voltage is specified @ full +/-Vs. So its larger than common mode input.
CM and Vdiff are two separate considerations. CM is referred to ground, whereas Vdiff just refered to input pins. Has to do with breakdown limits of on chip input diff amp structure.3) Some TI datasheets mention a VID value. But I have so far not been able to find out its meaning. Like the TI lmv7219 datasheet talks about an Output High Swing (why not simply output voltage?) at IL=4mA (I suppose the output current current drawn) with VID=500mV. Now for this example the Differential Input Voltage equals supply voltage, so I do not assume the "D" in VID stands for differential [input voltage.]
Vid is usually a test condition, which specifies overdrive conditions to trip the comparator. For speed and delay specifications.4) Some have a strobe pin. I have not been able to find out, what that practically means. I sure do not need it, but would like to understand its use, while we are at it.
From a representative datasheet (not necessarily the one you decide to use) -
A low-level input at either strobe causes the output
to remain high regardless of the differential
input.When both strobe inputs are either open or
at a high logic level, the output voltage is
controlled by the differential input voltage. 5) Additionally I have found latching and shutdown pins. I wonder, whether there is also a known model that features a reset switch? Like, as long as this pin is high, the output is low regardless of the inputs?
That would be a strobe pin.
Or could I even rely on Vout being definite groundlevel (V-), when SHDN is high and the device therefore disabled? With the help of a pulldown resistor maybe? Referring to the TI tlv3501 here, in case someone has experience with that particular chip.
6) The output low voltage is usually specified @ around 0.1-0.4V But since this is still above GND, why are some then sinking current? I understand sinking to be current flowing into the device? So occasionally you read somethig like Iout for low output swing is -15mA
The output low voltage is usually refereed to negative rail. Not ground unless negative rail grounded. The source current is telling you, for an output taken close to negative rail what you can anticipate getting out of the high side output driver in the output structure.
The output low is referred to negative rail. So the output transistor to ground in the output driver circuit is hard
on sinking any current coming from load referred to ground. The -15 mA is telling you, if your load is pulling
to ground (more appropriately the negative rail), but comparator is driving high, what current you can expect to source
out of the output high side transistor driver.Here is a general reference (OpAmps and Comparators similar in many respects) -
http://www.ti.com/lit/an/sloa011/sloa011.pdfRegards, Dana