LMH6642: Question of LMH6642 Input Range

Thanks a lot. My plan was: +/-12V pulse signal -> TL431 -> +2.5V/-0.6V -> LMH6642 -> GPIO

What is the switching threshold? What propagation delay do you need? Do you have other supply voltages?

Here is a section of my schematic, accompanied by the test results. The input signal is composed of +/-12V pulses with a 25us width (CH1). The TL431 is set to regulate the output voltage within a +2.0V to -0.6V range (CH2). I am in search of a comparator that can trim the rising edge of the TL431's output to make it compatible with the DAQ, which can handle up to +/-5V. The entire circuit operates on a single +3.3V power supply rail.

I can resolve the issue by replacing the LMH6642 with a TLV3201 comparator and introducing a resistive voltage divider between the TL431 and the TLV3201.

Hello Wayne,

Using the TL431 you could shift the voltage up from -0.6V to -0.1V.  This would solve your input limitation issue on the low end.

If you are using the LMH6642 as a comparator, could you not use it with this shifted input signal and take whatever the output is for +12V system input as your "HIGH" condition?

What output signal do you need from the LMH6642 as a comparator?

Could you not use the TL431, a resistor divider, and the LMH6642, as you mentioned with using the TLV3201?

Best,

Alec

Hi Alec, 

The TLV3201 datasheet states that "Input pins are diode-clamped to the power-supply rails. Input signals that can swing more than 0.5V beyond the supply rails must be current limited to 10 mA or less". Does this mean that the device can tolerate an input signal of -0.6V, as is produced by my TL431 output?






CH1: The input to the TL431 is a +/-12V square wave. CH2: The output from the TL431 ranges from -0.6V to +2.0V. I am researching a comparator to adjust the TL431's output back to a square wave form."



Thank you and Best regards,

Wayne Chen
07/15/2024

Hello Wayne,

I have time to look into your circuit tomorrow & Friday this week.

Thank you.

Best,

Alec

Hi Alec, Thank you for your suggestion. We have completed the validations with the TL431 and TLV3201... Wayne Chen

Hello Wayne,

Thank you for the follow-up.  If you need any buffers or gain stages in your systems, we have a range of high-speed amplifiers which can be options.

Using the LMH6642 as a comparator is not as easy or simple as using a comparator as a comparator .

Thank you.

Best,

Alec