LPV521: Amplifiers forum

Hi Meiling,

LPV521 is a nano-power device. Speed and power are direct trade-offs for amplifiers; lower quiescent currents usually correspond with lower GBW.

What is your application? Are you able to provide any other key-specifications or features you require for the recommendation?

Meiling 

thanks for your post  

unfortunately most amplifiers in SC70 package have the output on pin 4 while the nanopower lpv521 has the output on pin 1. Are you able to adjust the layout to accommodate the more common pinout? This would open you up for more amplifier options. 
Chuck 

TLV9001T is one amplifier with the same pinout as lpv521 but its GBW is only 1MHz

Hi Chuck,

We use LPV521 (see the above circuit)  to product a pulse signal to wake up CPU.  Our requirements is low power consumption (ok) and the frequency range is 3-400Hz (preferred at least 500Hz) but we found the LPV521 gain bandwidth is too narrow and the gain decrease when the frequency increase in our required frequency range, so LPV521 does not suit for our application.

We have made PCB already in this time and it is difficult to adjust the layout to accommodate a new version. Can you help us check if  TLV9001T is ok for our application.

In the future, we could change the layout. Can you recommend one for limited space and the above requirement

Best regards,

Meiling

sorry, the circuit did not get attached, please try to upload again

thanks, Chuck

Hi Chunk,

Here is the circuit.

Best regards,

Meiling 

Thanks. Now what is the input stimulus? Sounds like you’re just converting a low level input to square wave at the output. If that’s the case, a comparator is probably a better option. So please share input waveform details (oscilloscope waveforms) and confirm I’m understanding your design intends to create square wave output. 

Hi Chuck,

Many thanks for so quick reply to my question.

My application is to wake up CPU to do monitoring when railway trains is coming to my device. The device input is from a buzzer. The first wheel of trains interacted with rail will wake up my device installed on the trail.  The frequency of the wheel interactor with the rail frequency is 3-15 Hz (up to the train speed) but the rail transient vibration frequency can be 50-400Hz. The buzzer input is a pulse from impact force of wheels and the output of op-amp need to be a pulse or signal from 0 to 1 to wake-up the CPU. The op-amp need s to response to 400Hz. At the moment, it is just up to 20 Hz or 50 Hz with reduced output and it is not able to wake-up the CPU in the current design..

We want to wake-up the CPU and so we need to have a  little high frequency response (up to 400Hz, can be high).

We have used LPV521 but is does not work. So we want to use the same layout/pin chip but have a high frequency response. I hope it is clear in the information now and you can recommend a new chip with same pin and footprint?

Best regards,

Meiling

Appreciate the explanation but to be honest I’m still not exactly following your description. Regardless, our best option at this point is our tlv9001T assuming the circuit as you’ve shared is required. lf you have any waveforms to share, happy to review further to see if there’s anything else I can think of. 
Chuck

H Chunk, here is it. our input wave form is pulse or rectangular with 3 to 400Hz. our output wave form is pulse as well as long as there is from 0 to high. If you need to have more information, please let me know it. Best regards, Meiling

Hi Meiling,

I apologize for missing this. I read through your description again, and it seems like you want to have the op amp circuit detect the above waveform and wake the CPU up. I'm still having a bit of trouble picturing which node the input signal you've shared is at, but I have a couple of follow-ups. 

If the desired output is a 1 or a 0, wouldn't a comparator be more applicable to your application instead of an op amp? Some sort of latching comparator configuration to detect the first vibration pulse?

As for the op amp, there is another device with the same pinout with 10MHz GBW: LMV721-N/LMV722 10MHz, Low Noise, Low Voltage, and Low Power Operational Amplifier. Still, I'm still unsure what the ideal output pulse would look like. Would it be possible to share with us what the requirement for the output pulse is to wake up the CPU?