• State Resolved
  • Replies 10 replies
  • Subscribers 49 subscribers
  • Views 176 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

OPA2377-Q1: Applying voltage to output terminals of opamp

Gokhan G.
Intellectual 645 points
Part Number: OPA2377-Q1
Other Parts Discussed in Thread: OPA2377

Tool/software:

Hi,

I'm planning to use OPA2377QDGKRQ1 in mass production. After assembly at end-of-line testing, we need to apply voltage to the output terminal (pin7 and pin1) of this IC.

I couldn't find any information about sink current capacity and I needed to confirm application from TI side.

Q1) The VCC will be 3.3V and I'm planning to apply ~3V to output pin from (pin7 and pin1). Is it safe to do this? Does it damage my IC?

Q2) Does this application damage any component inside which leads problem in long-term usage? I meant some problems appear later on.

Q3) Does this application reduce life-time of component?

Thanks in advance.

  • 0
    Intellectual 645 points

    I forgot to add schematic. It is as below.

  • 0
    Guru 263750 points

    See figures 10 and 12 for how the output behaves. The absolute maximum ratings allow one output to be shorted to ground.

    Would it be possible to inject the voltage at the other side of the R, directly at the ADC pin?

  • 0
    TI__Guru 62290 points

    Shorting OPA2377 output to 3V with Vcc of 3.3V is safe BUT will result in up to +30mA/-50mA short circuit current.  For this reason, in order not to damage metal traces inside the package or exceed the maximum junction temperature of 150 deg C, only one output should be shorted at any given time - see below.

  • 0 in reply to Marek Lis
    Intellectual 645 points

    Hi,

    If I apply 3V to directly output terminals, how much current will flow inside of OPAMP? Is there any internal resistance?

    There is 100R and 200R resistance at RC side for dual opamp, total current from 3V to output pins as total if it is shorted inside will be -45mA. It seems safe for datasheet but may there be thermal problem right?

  • 0 in reply to Gokhan G.
    Guru 263750 points

    Figures 10/12 show how much current can flow, depending on the temperature and on what voltage the opamp tries to drive.

    The power dissipation will be 45 mA × 3 V = 135 mW, so the junction temperature will be 135 mW × 171.2 °C/W ≈ 23 °C over the ambient temperature.

  • 0 in reply to Clemens Ladisch
    Intellectual 645 points

    Hi Clemens,

    I think the calculation is wrong. The power loss will be on resistance not inside of opamp. The internal output resistance will be critical.

    Gokhan G. said:

    If I apply 3V to directly output terminals, how much current will flow inside of OPAMP? Is there any internal resistance?

    Can you help on for my above question?

  • 0 in reply to Gokhan G.
    Guru 263750 points

    When the opamp tries to drive its output to near 0 V, but the output is forced to 3 V, then the power is dissipated inside the opamp.

    Is the schematic correct, or are you injecting the voltage at the right side of the R?

  • 0 in reply to Gokhan G.
    TI__Guru 62290 points

    Gokhan,

    At the output the only resistance is the close-loop output resistance which comes to play ONLY under linear operation (Ro->0).  However, this is not the case under fault condition - if your injected 3V supply that can deliver Isc current, Vout will be pulled to 3V (despite the OPA2377 trying to drive it to zero) and the entire voltage drop of 3V will be inside the package; thus, Clemens is correct in the calculation of power dissipation inside the package: Pdiss=3V*Isc - see below.

    Having said that, this condition is unlikely to result in junction temperature above 150deg C and thus is safe.  However, this does not change the fact that the internal power supply traces can support only one channel to be short-circuited and shorting both output at the same time, resulting in total of 100mA sinking current, could damage metal traces inside OPA2377.

  • 0 in reply to Marek Lis
    Intellectual 645 points

    Hello Marek,

    So if I apply 3V directly to the OUT pin, then which mechanism will limit current to Isc. I just couldn't understand that point. If my power supply can provide 100A, the IC will blow.

    In real application, we will apply 3V to the MCU pin side to limit current on resistor according to your recommendation.

  • +1 in reply to Gokhan G.
    TI__Guru 62290 points

    Gokhan,

    When you apply 3V to OUT pin, the internal Isc circuitry of OPA2377 will limit the current to around 50mA (see below).  Since you say that your power supply can deliver much more current than Isc, it will pull the OUT pin of OPA2377 to 3V and you will see the condition as shown in my previous reply and IC will be fine sinking ~50mA.