• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 1185 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

OPA170 / about voltage output swing

Toshiyuki
Mastermind 7075 points

Other Parts Discussed in Thread: OPA170

Hi,

Our customer is considering whether OPA170 could be used in terms of  linearity.

Then, they would use OPA170 up to Vo=35V@Vs=36V and Iload=3.5mA.

Would you please provide us the voltage output swing spec(MIN,MAX)@Iload=3.5mA?

Best Regards,

Kato

  • 0
    TI__Guru* 93105 points

    Hello Kato-san,

    Please understand that the OPA170 voltage output swing (Vo) are only assured for the specific conditions listed in the datasheet Electrical Characteristics table. We cannot assure any specific minimum/maximum performance unless it is specifically listed in the table. Thus, MIN, MAX limits for an ILOAD of 3.5 mA cannot be assured. All we can provide is an estimate.

    Datasheet Figure 9, Output Voltage Swing vs Output Current (Maximum Supply), which is shown below, provides a good estimate of how close the OPA170 output swings under the influences of load current and temperature. I added an orange vertical line at ILOAD equal to +/-3.5 mA.

    The graph shows that the lowest OPA170 Vo occurs when it is sourcing -3.5 mA to a load at a temperature of 125 C (red curve in upper graph). The Vo level appears to be about 17.3 to 17.4 V. It might be a little lower across different production runs, over time. I wouldn't expect it to be less than 17 V.

    The high end for Vo appears to be similar in level for both when the OPA170 is sinking +3.5 mA, and sourcing -3.5 mA, at -40 C. It looks to be about 17.7 to 17. 8 V. I really would rely on it being much higher.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Mastermind 7075 points

    Hi Thomas - san,

    Thank you for your support. I considered the variation of voltage output swing  for an ILOAD of 3.5mA.

    I believe that the output voltage vs output current specific has linearity up to 5mA. 

    When calculated from Figure 9,

    Vo(25C) drop[TYP] = 0.5V @5mA -> Ron = 100Ω

    Vo(125C) drop[TYP] ≒ 1V @5mA -> Ron = 200Ω

    When calculated from datasheet Electrical Characteristics table,

    Vo(25C,IL sourcing) drop[MAX] = 115mV @1mA -> Ron(25C)[MAX] = 115Ω

    From the above, I calcutaed the worst case of Vo drop at 3.5mA.

    Ron(125C)[MAX] ≒ 200Ω x 115/100 ≒ 230Ω

    ∴Vo(125C,IL sourcing 3.5mA)drop[MAX] = 3.5mA x 230Ω ≒ 0.8V

    If 36V supply is used, I believe that voltage output swing (125C,IL sourcing 3.5mA) is about 34.2V[MAX].

    Is my understanding correct ?

    Best Regards,

    Kato

  • 0 in reply to Toshiyuki
    TI__Guru* 93105 points

    Kato-san,

    The RON resistance of the output transistor can be approximated using the datasheet Figure 9 curves, Output Voltage Swing vs Output Current, using the relationship:

    RON ≈ Δ VOUT / ΔIOUT 

    The upper curves are for the upper transistor sourcing current, and the lower curves are for the lower transistor sinking current. The transistors are different in design and their RON are different because of that, but that isn't an issue when they are operated within their common current range.

    Using the curves the RON can be estimated at each temperature. I estimated the voltage and current changes from the curves. For the upper set of curves:

    +125 C    RON ≈ Δ VOUT / ΔIOUT   = 2 V/ 9 mA = 222 Ω

    + 25 C     RON = 1V/ 9 mA = 111 Ω

    -40 C       RON = 0.75 V/ 9mA = 83 Ω

    For the lower set of curves: 

    +125 C     RON = 0.9 V/ 9 mA = 100 Ω

    +25 C      RON = 0.5/ 9 mA = 56 Ω

    -40 C       RON = 0.5/ 9 mA = 56 Ω 

    Using these RON values you should be able to approximate the voltage drop across the output transistor based on the current through it and the ambient temperature of the OPA170. RON should not change much when a different supply voltage is applied to the OPA170.

    Regards, Thomas

    PA - Linear Applications Engineering