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THS4541: THS4541

HD
Prodigy 160 points
Part Number: THS4541
Other Parts Discussed in Thread: BUF634, OPA863

Hi,

I need support about this component.

We have to convert a single-ended pulse 0-3.3V Tduration =15ns f=50kHz (generated by a microcontroller and a high speed TTL buffer) into differential pulse. The gain can be unity.

We want to use THS4541. Can you help us to design a simple solution?

Thanks for your support.

  • 0
    TI__Expert 6050 points

    Hi,

    I would be happy to help design a solution to fit your application. Can you clarify a few things first:

    1. My assumption is that you are using a 5V single supply configuration. Please correct me if this is a wrong assumption.

    2. What load will be on the output of the amplifier?

    3. Are you planning on operating Vocm at midsupply? If operating at a Vocm that is not close to midsupply, you may starting running into output headroom limitations.

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    Prodigy 160 points

    Hi Nick,

    1. Yes, 5V single supply configuration

    2. The load is MAX3869

    3. Vocm=2.5V

    The input signal is a train of pulses 0-3.3V, Td=15ns, f=50kHz.

    Thanks for your support.

  • 0 in reply to HD
    TI__Expert 6050 points

    Hi,

    Based on the requirements you listed below, I designed the below circuit.

    If you need to remove the overshoot, you can add some feedback capacitance (around 1 to 10pF is a good starting point). This will remove most to all overshoot at the cost of increased rise time. I have also attached the TINA schematic that you can use to simulate and make any adjustments as you need.

    THS4541_E2E.TSC

    Thanks,

    Nick

  • 0 in reply to Nick Nauman
    Prodigy 160 points

    Hi Nick,

    attached an updated TINA schematic using all 1K resistors to have 1V/V.

    1. There is a reason why you suggest 425R and 402R?

    2. We want use an high speed buffer between micro (VG1) and THS4541, for example BUF634, but the simulation fails when we use single supply; it is an      issue related to the simulator or the buffer cannot work with single supply? The datasheet says that it is good also for single supply.

    3. Beyond the classic differential routing rules, any hint about connection between micro and THS? I refer to matching, reflections etc.

    Thanks.

    Best Regards.

    THS4541_E2E_updated.TSC

  • 0 in reply to HD
    Prodigy 160 points

    In the case of 425R we have a Rin=566R and gain 0.945, otherwise with 1K we have Rin=1333K and unity gain.

  • 0 in reply to HD
    TI__Expert 6050 points

    Hi,

    1. Section 9.4.1.3 of the datasheet, Table 6, has recommended resistor values for each gain setting. These resistor values are selected to try to achieve the best noise performance, harmonic distortion, and for any noise gain peaking. All device behaviors are characterized using these values (unless otherwise specified). You can use different resistor values, however, the performance may not be the same as what is characterized.

    2. The BUF634 is capable of running in a single supply configuration. However, I believe that you are seeing a convergence error because of the input voltage that you are feeding the buffer. I would recommend looking at a device like the OPA863 that can be set in a buffer configuration. Is there a reason you chose the BUF634?

    3. Section 9.4.1.4 of the datasheet address this question pretty well I believe. To summarize, because you plan to buffer the input voltage between the microcontroller and the FDA, it is not necessary to use any impedance matching and therefore Rg will be the same for Vin+ and Vin-.

    Thanks,

    Nick