TLE2062 Excess Current

Hi Mark,

Can you provide your circuit schematic?

Is there a specific reason you want to use an operational amplifier as a comparator?

Regards, Thomas

PA - Linear Applications Engineering

Hi Thomas,

The circuit is in an existing product that has been around for 20 years.  It is a very dense module, so the designer used 1/2 of the part for the comparator, as there was no room for a separate chip.  Originally, the TL032MJG was used, but is no longer available, so we are trying to switch to the TLE2062MJG.  The TL032MJG does not exhibit this phenomenon.  I have created a test circuit, which closely resembles the real circuit.  The test circuit has the + input (pin 3) to a 1k resister, which is then hooked to ground.  I am feeding a voltage source (0 to 2.5V) into the - input (pin 2) through a 100k resister.  The supplies are ±15V. 

Thanks,

Mark

Mark,

TLE2062 with its bipolar transistor output stage (see below) is poorly suited to be used as a comparator.  Since comparator function requires the output to collapse on one of its rails,  this forces the output bipolar transistors to operate in a fully saturated state (transistor's beta goes to ~1), which completely changes the output stage quiescent biasing condition with respect to its normal linear operation; the output stage becomes mis-biased, resulting in much higher total current,IQ, than specified in PDS.

Hi Marek,

Thanks for the very knowledgeable reply!  Is there another pin compatible replacement for the TL032MJG that comes to mind for this?

Thanks again,

Mark

Mark,

For low power supply application (5V or +/-2.5V),  I could recommend several op amps that might be used as comparator ( OPA2313, OPA2314, OPA2376, OPA2340) but for +/-15V supplies voltage the only op amps I could suggest is OPA2140 or OPA2141 - make sure, however, that you do not violate its upper common-mode input range limit of Vss-3.5V; also, we have OPA192 coming out that would satisfy your high supply requirement but it won't be available for the next few months.

Hi Mark,

Ideally, a true dual comparator product would be best for this application. They are designed to operate with their output at one output rail, or the other, and recover quickly from the saturated condition.  The pin out for many dual comparators is the same as that of most dual operational amplifiers. The main issue with trying to use a true comparator in your application is the output is most often open collector, or open drain, requiring a pull-up to the positive supply rail. The operational amplifiers on the other hand provide a push-pull output not requiring a pull -up.

When I review the TI comparator comparator offerings none of the dual devices that operate from +/-15 V supplies have a push-pull output; but I may have missed something in my search. If I find one that I think will work as a replacement for the TLE2062MJG I will post another response here.

Regards, Thomas

PA - Linear Applications Engineering

Thanks Marek and Thomas.  Unfortunately, it looks like the OPA214x are not available in a DIP package.   

I definitely appreciate all the help and feedback on this issue!!

Best regards,

Mark