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OPA1692: output amplitude with different load

Kailyn Chen
Genius 9560 points
Part Number: OPA1692

Hello，

According to the  Figure 13. Maximum Output Voltage vs Frequency of OPA 1692, we could get to the conclusion about  the output amplitude is more than 4Vp when the Frequency less than 1Mhz with +-5V,2Kohm load. So if the power supply is 8V, and the load is decreased to 1Kohm, does it the output amplitude get to 4Vrms（5.66Vp）？Our customer want to select one audio amplifier which need to get to 4Vrms output with 1Kohm load. I think the OPA1692 could meet his need. Do you have any other opinions?

Best regards

Kailyn 

  • 0
    TI__Mastermind 23580 points

    Kailyn,

    1. What frequency will the customer operate the device at?
    2. Is the customer operating in inverting or non-inverting configuration?
    3. Is the supply voltage +/-8V?

     

    Considering the provided information I have simulated and attached the file that can be used for analysis. I have the device configured in a gain of -1 with an input sinusoid at a peak voltage of 5.656V amplitude. This is with a frequency of 1kHz however so I would like to reproduce with the answers to the questions above. I did provide the plot for a 1MHz transient response for comparison and you can see the output signal does reduce to 4.25V Peak. 

    The peak output current will be 5.656V/1kohm = 5.656 mA. This can be seen in the plot below with the AM1 plot for the 1kHz case.

    Also considering this current and looking at the Output Voltage vs Output current plots of Figures 46 and 47 for both sourcing and sinking current respectively, we see that the operating current is well within the acceptable drive strength of the output stage.

    Depending on the gain of the amplifier and the operating frequency the output can droop as you approach the closed loop bandwidth of the circuit. In our simulation with the reference design (attached) you can see the gain peaking around the 1Mhz region in gains of +/-1. I have put this image below as well (Closed loop Gain vs Frequency). This information will help us decide if it will provide the customer the desired behavior.

    1kHz Sine wave transient response:

    1MHz Sine wave transient response:

    Gain Peaking occurs as shown below for gains of +/-1:

    OPA1692 Sim_sbomaf2b.TSC

  • 0
    TI__Mastermind 23580 points

    Kailyn,

    Also, what is the gain the customer is using?

  • 0 in reply to Chris Featherstone
    TI__Genius 9560 points

    Hi Chris,

    Thank you very much for your reply. I would confirm with the customer again. 

    Best regards

    Kailyn 

  • 0 in reply to Kailyn Chen
    TI__Mastermind 23580 points

    Kailyn,

    The full power bandwidth curve shown in Figure 13, also known as the Maximum output voltage vs Frequency curve shows the maximum output voltage at different frequencies that the device can provide on its output. As an example I have drawn a red dashed line at a frequency of 1MHz. You can see that at most the output voltage can get to roughly 3.6V peak. This is true for both the supplies of

    Vs = ±15V, and Vs = ±5V.

    This can be calculated by taking the slew rate divided by 2πf.

    2πf *Vout ≤ S.R

    The slew rate from the OPA1692 product datasheet is 23V/us. The frequency example is

    Therefore

    This calculation matches the graph below.