• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 48 subscribers
  • Views 429 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Recommended ADC + Transimpedance-Amplifier and schematic to measure nanoamps currents

Javier Arigita Lopez
Prodigy 30 points
Other Parts Discussed in Thread: INA190, PGA281, LMC6001, OPA3S328, OPA392

Hello,

I have to find a way to measure the leakage current of GaN or SiC-Mosfets in a HTRB test. These currents are in the range of 15nA to 1mA and therefore the voltages at the input of the ADC will be minimal and would require a high amplification and noise rejection. Due to the device under tests that we use, the voltage over the switches can get as high as 6kV. Do you have any clue about a possible Transimpedance-Amplifier + ADC and Schematic that I could use for this use case?. Additionally I will have to think about the isolated power supply and SPI lines.

Thanks,

Javier

  • 0
    TI__Mastermind 19395 points

    Javier,

    From the current sensing side of the house, the INA190 is the only product in our portfolio that would be capable of measuring nanoamps, due to the 3nA max (500pA typical) input bias current exhibited by that device. I would recommend having a look at this device, but I am also going to loop in the team supporting transimpedance amplifiers, since this is the solution you requested here. Please let me know if you have any questions on the INA190. 

  • 0
    TI__Mastermind 25765 points

    Hello Javier,

      That is a large range of currents, maybe a programmable/variable gain amplifier might be necessary. The complexity in a TIA design in this specific application stem from the wide range in changes of the capacitance from the FETs as you increase/decrease Vds. This makes it complicated to narrow it down to an input capacitance which is important for choosing the feedback compensation capacitor for circuit stability. 

      I would probably suggest a precise variable gain amplifier with a input shunt resistance. As Carolus said, it is important to look at bias currents for current sensing applications as some amplifiers, especially bipolar, will probably be over the nA range. These two references design should be helpful: TIPD104 and TIPD135. The first one uses an instrumentational amplifier in low-side sensing (common mode voltage 0V) with selectable gains (would replace INA with LMC6001). The second one uses a PGA (selectable gains), but in high-side sensing. The PGA281 in the reference design has a max input bias current of +/-2nA.

      Moving this thread to PGA/VGA within precision amplifiers, but might be later forwarded to general purpose amplifiers. 

    Thank you,

    Sima 

  • 0 in reply to Sima Jalaleddine
    TI__Genius 12505 points

    Hello Javier,

    From the Precision Amplifier team, we have several devices that can be used as a TIA.  I'll assume at the moment you have a low voltage, isolated, floating supply, for which I will recommend a few low-voltage amplifiers that can work well.  the OPA3S328 is a device specifically defined to be used as a transimpedance amplifier that can also drive SAR converters.  It has integrated switches and two amplifiers that have 300 ns settling time.  The data sheet below gives a few examples of TIA circuits:

    https://www.ti.com/lit/ds/symlink/opa3s328.pdf

    The switches on the 3S328 make it ideal for switched-gain TIA applications, allowing for several decades of current measurement.

    If you need a lower bandwidth/lower power solution, the OPA392 is a low input bias current amp. that can work well as a TIA.

    https://www.ti.com/lit/ds/symlink/opa392.pdf

    Let me know any feedback on either of these two, and we can follow up with additional recommendations.

    Best Regards,
    Mike