Part Number: LM139
I'm looking for replacing the quad-comparator LM139AD with a component with the same features but more tolerant to negative voltage.
Indeed, the power supply is +15/GND, and I would like a quad differential comparator which is not changing state even if the input voltage Vin- goes below -0.3V (with a min input voltage of -0.8 for instance).
Is such a component available ?
Thanks in advance.
We are glad that we were able to resolve this issue, and will now proceed to close this thread.
If you have further questions related to this thread, you may click "Ask a related question" below. The newly created question will be automatically linked to this question.
These devices are pretty rugged, but negative voltages are their Achilles heel.
The problem is that you will end up forward-biasing either the die substrate diode (for these older JI processes) or the ESD protection structures (in "modern" CMOS and Bipolar devices).
Most of the comparators will allow up to -0.3V, since this is before the diodes conduct. The diodes start to conduct around 400mV and would be in full conduction at -600mV to -800mV - so that limits the input range.
I am not aware of any comparators that can handle negative voltages beyond -0.3V.
Your best solution is to add series resistance (1k min per volt) to the input and a Shottky clamp diode to keep the clamp close to -350mV. Clamp current should be limited to 1mA or less.
Depending on the circuit and the tolerances, you may also be able to attenuate the input enough to bring the negative voltage above -0.3V (and shift the threshold accordingly).
How the comparator behaves when the input is taken below the limit varies by the device family. You may have to try different devices, over temperature, to see if they misbehave. Still...it is not a good idea to rely on a particular unspecified behavior, since that can change over time.
Do you need the Military temp range? Mil temp range and 15V quad really narrows the available selections. Not all Quads have the same pinout (usually either the LM139 pin-out or the standard quad op-amp pin-out).
Try the TLC374M. It is a drop-in replacement CMOS version (16V max) and see if it is more tolerant, but I still recommend the clamp or attenuation.
Low Power Amplifiers and Comparators (LPAC) Applications
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.