Problems with LT1719

[Caleb]

Hello,

does anybody know a pin-compatible type of comparator which fits to a LT1719 footprint?

I have strange problem with the LT1719 ... i set a reference voltage by a 12bit DAC to -IN-Pin of the circuit ... the relevant range is from 240mV to 300mV. I supply the LT1719  a constant current/voltage and change the the DAC-value ... but in some areas the LT1719 behaviour is not linear =( The problem must be the LT1719 ... because the reference voltage of the DAC is absolutely linear all over the range. It seems that the LT1719 changes the potential of +IN-Pin in particular areas of the reference voltage. With another comparator (not LT1719) it is absolutely linear.

Somebody else has seen such a problem?

Sorry for bad english =/

[HackedFridgeMagnet]

Your problem is probably the hysteresis in the comparator, this is what makes it a comparator, as opposed to a (not very linear) opamp.
Its hard to explain but basically it is slightly reluctant to change state. So to flip the output you need to go a little bit past equal voltages on the inputs. Maybe 10mv-30mv it should be on the datasheet.



Maybe an op amp would suit your purposes better. It is linear and has no hysteresis and as long as you dont use feed back it will go near to the rail.

[Caleb]

Thanks for your reply.
You could be right ... i tried it with another comparator ... a LT1671 (with no internal hysteresis) ... this one shows wonderful linear behaviour.

I'll check your suggestions