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OPA2206: Overvoltage protection

John Griffith
Mastermind 21543 points
Part Number: OPA2206
Other Parts Discussed in Thread: OPA627

Hello,

Do we have any information about how the integrated overvoltage protection compares performance wise to external OVP clamping? Does it offer less distortion? From the datasheet it appears to only activate after the supply rails have been exceeded so it seems like it would add very little distortion for the nominal input range within the supply rails except for the small series impedance. 

Customer is considering the ADA4177 in addition to the OPA2206. 

Thanks,

John

  • 0
    TI__Guru 63760 points

    Hi John,

    We do not have information on how the integrated overvoltage protection compares performance wise to external OVP clamping but it definitely offers less distortion.  This is because in order to limit the input current under overvoltage condition of +/-40V beyond the rails to the required 10mA (max current through ESD protection diode-see below), one would need to add 4kohm series input resistors that would also be there causing distortion during normal operation with Vcm within the rails.  However, the integrated OVP clamping is done with back-to-back JFET transistors (they are effectively a voltage controlled resistors) that provide very low impedance (thus, no distortion) within the rails and their impedance increases only when the Vcm is taken beyond the rails where the signal is grossly distorted anyway due to the non-linear operation of the input stage - see below.   

  • 0 in reply to Marek Lis
    TI__Mastermind 21543 points

    Thanks for the quick response! That is what I had said to the customer but wanted to see if there was anything else I was missing.  I am trying to learn more about where the engineer is trying to use the device and if this device will work. He originally asked for a single rail 3.3V supply op amp with the ability to handle short to 48V. This device needs 4.5V single rail, and can only handle 40V over V+ - so not a perfect fit, but it doesn't look like anyone else has this either.

    Any other devices or ideas on how to hand single rail 3.3V and 48V OVP? Some INA8xx devices look to have ±60V protection but they also need 4.5V and are not a standard op amp. Let me know what you think.  

    John 

  • 0 in reply to John Griffith
    Guru 140200 points

    Hi John,

    there are several possible remedys. But one would need to see a schematic and to know more about the application.

    One idea is to install an additional diode clamp or external back-to-back JFETs. Another idea is to operate the OPAmp as an inverting amplifier with the +input of OPAmp being connected to signal ground and to clamp the voltage at the -input of OPAmp -which is sitting on virtual ground- to signal ground. See figure 33 of datasheet of OPA627, for instance. But again, one would need to see a schematic and to know more about the application.

    It should also be kept in mind that active protection circuits like back-to-back JFETs or diode clamps may not work instantaneously but may need some time to fully settle. Because of that, the OPAmp might not survive a sudden, abrupt and sharp short-circuit to a very low ohmic +48V. So, it would be wise to add some low pass filtering to the input to allow the protection circuit to properly operate in time. This not only to slow down the rise time of overvoltage spike but also to provide some passive current limiting and by this to protect the protection circuitry Relaxed

    Usually, you have to pay a price when adding robust protection circuitry against entirely abnormal overvoltages and it may be a better idea to prevent these overvoltage conditions by other measures from the start.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 21543 points

    Thanks! I think in some cases, like a harness wire fault where one of the conductors is 48V and another is the input to the amplifier, cannot be avoided and have to be protected at the amp or internal to the amp. Waiting to hear back more from the engineer.

    John