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OPA462: OPA462 Circuit design 100-5V, but only 24-5V why

Daisuke Nomura
Intellectual 1010 points
Part Number: OPA462


Tool/software:

I would like to know about the TI op-amp OPA462. I am creating an amplifier circuit using the above product, but I am not able to amplify as I would like. I have created an inverting amplifier circuit with a magnification of about 20x. 80V is applied to V+ and GND is connected to V-. I am expecting 100-5V to be output when 5V is applied to IN+ and 0-5V is applied to IN-, but the actual output range is 24-5V. The output becomes 24V when IN- is around 4V, and it seems to be capped. Since RL is 10kΩ, I thought it would be possible to output up to V+-1.5V (78.5V in this case). What do you think is the reason why it is capped at 24V? *Other terminals are connected as follows. E/D terminal: 5V E/D com: GND Status Flag: N.C

  • 0
    TI__Genius 13845 points

    Hello Nomura-san,

    Can you attach a schematic?  I'm not sure what you are referring to when you say "5V is applied to IN+" and "0-5V is applied to IN-"; is that referring to the inputs of the amplifier?  

    I suspect this is related to the input common mode range of the amplifier - the common-mode input voltage needs to be above 1 V from the negative rail:

    If this is inverting, then that means the non-inverting terminal needs to be at least 1 V if the negative supply is above ground.  

    Please clarify the configuration and we can go from there.

    Regards,
    Mike

  • 0 in reply to Daisuke Nomura
    TI__Intellectual 1010 points

    Michael-san,

    Thank you for your reply. Let me continue with customer question. As shown in the attached circuit, the + terminal on the input side is fixed at 5V, and the - terminal fluctuates between 0 and 5V depending on the device. They want to amplify the output to 100 to 5V according to the 0 to 5V input. After inputting -5V to the V- terminal instead of GND and changing the resistance value of the inverting amplifier circuit through trial and error, They were able to amplify to around 80V. Ultimately, They would like to amplify to around 300V, but would you be able to introduce any other op-amps other than this one that are suitable?

  • 0 in reply to Daisuke Nomura
    TI__Guru* 77541 points

    Hello Nomura-san,

    Daisuke Nomura said:
    They want to amplify the output to 100 to 5V according to the 0 to 5V input.

    Here is the example that may meet your requirements. My guess is that the customer's load may be lower than 10kΩ and limited output swing at 80V.

    OP462 is unable to source higher current more while still capable to maintain the output headroom. Please check on the resistive load at the output.   

    OPA462 5V to 100V 09162024.TSC

    Daisuke Nomura said:
    They would like to amplify to around 300V, but would you be able to introduce any other op-amps other than this one that are suitable?

    For 300V output swing application, the customer may have to use the bootstrap technique for now, see the attached application note. 

    https://www.ti.com/lit/an/sboa510/sboa510.pdf?ts=1726501338259&ref_url=https%253A%252F%252Fsearch.yahoo.com%252F

    If you have other questions, please let us know. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Intellectual 1010 points

    Raymond-san,

    Thank you for your reply. customer understand that there is a method of bootstrap, and also that the OPA462 is used in the range of ±90V or 0~180V. Customer  think that the allowable voltage range of the OPA462 is not sufficient to achieve a 300V output,  is their understanding correct? Or is it possible for the OPA462 to handle 300V if I use the bootstrap method? I apologize if I am saying something off the mark, as I do not understand the bootstrap method. If it cannot be achieved with the OPA462, I would like to know of a product that can. 

    Thanks and best regards,

    Daisuke Nomura

  • 0 in reply to Daisuke Nomura
    TI__Guru* 77541 points

    Hello Nomura-san,

    Daisuke Nomura said:
    Customer  think that the allowable voltage range of the OPA462 is not sufficient to achieve a 300V output,  is their understanding correct?

    The understanding is correct. OPA462 on its whole is unable to support 300V output. 

    With OPA462 bootstrapped technique, then the 300Vpp can be achieved, as presented in the application note. 

    Enclosed is a HV simulation. 

    OPA 3X-462 09182024.TSC

    Daisuke Nomura said:
    If it cannot be achieved with the OPA462, I would like to know of a product that can. 

    We do not have single 300V power amplifier to meet the requirements. Our competitor AD has one, I recalled. Else, you can try APEX power amplifier (but the cost is high). 

    https://www.apexanalog.com/

    What is the HV application? If you tell me the detail, I may be able to come up with other options. 

    Best,

    Raymond