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LMH6722: About Feed back resistor

Tsukui Yusuke
Guru 21930 points
Part Number: LMH6722


Hi,

The data sheet contains the following information.

I have a question about this content.

１．When used as a buffer, the data sheet states that a 600Ω feedback resistor is required for stable operation.
　　On the other hand, Is this resistor required when used as a buffer for unused circuit treatment?

２．What is the operational impact of connecting an unused circuit buffer without a feedback resistor?

３．Is it necessary to connect a resistor between GND for non-inverting input?

Best Regards,
Yusuke

  • 0
    TI__Genius 15565 points

    Hello Yusuke,

    1&2) Yes, when using a current feedback amplifier you should always have a feedback resistor even for an unused buffer. Otherwise the amplifier will be unstable and oscillate. This will also increase power consumption, degrade the device over time if done for long periods and possibly affect other channels (if you are using a multi-channel parts).

    3) The resistor at the non-inverting input is a 50-ohm resistor that is used for impedance matching. This is needed in order to avoid reflection issues in high frequency applications. 

    Best,

    Hasan Babiker

  • 0 in reply to Hasan Babiker31
    Guru 21930 points

    Hell Hasan-san,

    Thank you for your kind support.
    Please let me ask one more question.

    Currently, the inverting input pins and output pins of unused circuits are opened.
    Non-inverting input pin is connected to GND.
    Is there any problem with the above terminal processing methods?

    Best Regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Genius 15565 points

    Hello Yusuke,

    We do not recommend leaving the pins of the unused amplifier as open connections. You can read more on this in the link below:

    http://www.ti.com/lit/an/sboa204a/sboa204a.pdf

    As I mentioned the only difference with a current feedback amplifier is you should add a feedback resistor between the output and IN-. If you dont care about the performance of this device, you can use a resistor value greater than the recommended 600 ohms. Also, using GND in the non-inverting pin is fine if you are using a dual supply configuration, but in a single-supply configuration you should set your input to mid-supply.

    Best,

    Hasan Babiker