Open-Collector Comparator

[alec_t]

so even though the lt1716 is an open collector output

It isn't open collector. Re-read post #4 and the datasheet.

 

[Nigel Goodwin]

Ok thank you ,
so even tough the lt1716 is an open collector output ist doesnt need an externel pull up resistor, right?

If it's open collector then it needs a pull-up resistor - although it could easily be part of the rest of the circuit.

What have you got against pull-up resistors?

 

[boro3]

No Problems with pull up resistor
Just wanted to understand the things right

It isn't open collector. Re-read post #4 and the datasheet.

Ok in this case, i am not sure why, but i thougt it is an open collector ..

Thank you all again

 

[MikeMl]

Ok thank you ,
so even tough the lt1716 is an open collector output ist doesnt need an externel pull up resistor, right?

The 1716 is unusual. It is simultaneously a push-pull (between Vdd and Vss) totem-pole output AND it can act like an open-drain pull-down where the external load is connected between the output pin and a voltage source more positive than Vdd.

If you connect nothing, and monitor the voltage at the output pin, you will see it switch between (Vss+few mV) and (Vdd-few mV). If you connect a pull-up resistor (or a load) between the output pin and +30V (for example), then you would see it switch between (Vss+few mV) and (30V).

 

[KeepItSimpleStupid]

yea, unusual.

The specs of source current of 5 uA and sink of 5 mA, sort of, puts it in a class of a non-open collector output. It does that to save power.

It also states that you can pull it up to voltages, including ones greater than the supply voltage, so that makes it open collector. The actual logic level of the output would change slightly. When pulled up, it should be equal to the supply voltage. When not pulled up, the high is within 55 mV of the positive supply. The lows are within 35 mV of the negative supply.

 

[eTech]

yea, unusual.

The specs of source current of 5 uA and sink of 5 mA, sort of, puts it in a class of a non-open collector output. It does that to save power.

It also states that you can pull it up to voltages, including ones greater than the supply voltage, so that makes it open collector. The actual logic level of the output would change slightly. When pulled up, it should be equal to the supply voltage. When not pulled up, the high is within 55 mV of the positive supply. The lows are within 35 mV of the negative supply.

Hmm...looking at schematic of the part....I don't see an open collector...the output looks like a push/pull arrangement. So should be able to pull the output either up or down. Won't be able to source much current though if pulled down.

eT

 

[KeepItSimpleStupid]

Hmm...looking at schematic of the part....I don't see an open collector...the output looks like a push/pull arrangement. So should be able to pull the output either up or down. Won't be able to source much current though if pulled down.

In the strictest sense - TRUE.

The ABILITY to pull the output to a voltage above the supply voltage also negates the strict definition of PUSH_PULL.

 

[eTech]

In the strictest sense - TRUE.

The ABILITY to pull the output to a voltage above the supply voltage also negates the strict definition of PUSH_PULL.

The output configuration also negates (if that's a word ;-)) the strict definition of an open collector.

 

[ChrisP58]

The input stage of the LT1716 is also unusual.

In post #15 you ask about having one of the inputs at +8V with the supply at only +5V. With most comparators that wouldn't work. But, due to the "Over-The-Top®" feature of the LT1716, that voltage combination is OK with this part.