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OPA2350: OPA2350 slew rate

Narendra S10
Intellectual 470 points
Part Number: OPA2350
Other Parts Discussed in Thread: TLV3501, TLV3502, OPA350, TLV3202

Hello all,

In one of my pulsed amplifier application,

I am using the OPA2350 OPAMP as comparator to detect the RF pulsed power and put a threshold on the health.

The pulse width is 200ns to 10us.

I am facing the following Issues.

1. The pulse width shrinks by 50 ns (because of slew rate). Can you suggest a similar OPAMP with same package(SO8) which can work for the specified narrow pulse width (higher slew rate).
2. I am not able to set the comparator voltage beyond 1.7 volt (with load). works fine without load.

I have attached the reference schematic (buffer,amplifier and comparator,buffer)

Please suggest

Regards

Narendra

  • 0
    TI__Guru* 93105 points

    Hello Narendra,

    A very fast 5 V CMOS comparator that is available in the 8-pin SOIC (D) package is the TLV3501. It has a typical propagation delay time of 4.5 ns, and maximum of 6.4 ns (TA = 25 C).

    https://www.ti.com/lit/ds/symlink/tlv3502.pdf

    A bit of an issue is you are using an OPA2350 dual op amp for U3A and U3B, and it looks like you only want to replace U3A with the comparator. U3B would remain a buffer amplifier. Correct? That means you would have to do a PCB change to accommodate the TLV3501 at U3A, and then make U3B an OPA350 instead of half of an OPA2350. If you can change both U3A and U3B to comparators the dual of the TLV3501 is the TLV3502; however, it uses a different pin layout than the OPA2350.

    There is a fast, but somewhat slower than TLV3501 comparator that uses the same SO-8 package pin assignments as the OPA2350. It is the TLV3202. As a first step you could try it on your board and see if the circuit performs to your satisfaction.

    https://www.ti.com/lit/ds/symlink/tlv3202.pdf

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Michael Steffes
    TI__Guru 56941 points

    Hi Narendra,

    You should use comparator, instead of Op Amp operated as comparator, especially your pulse width can be as short as 200nsec. 

    Comparator does not have limited slew rate, because it does not design with compensation capacitor internally, and last driving stage is a simply comparator, which it operates in high or low in saturation of the supply rails. Op Amp is operating linearly in Vout vs. Vin; its last driving stage is a buffer typically, and the size of internal compensation capacitor limits in its slew rate. 

    I am not able to set the comparator voltage beyond 1.7 volt (with load). works fine without load.

    You may use some low voltage comparator, say 1.8V comparator or place a zenzer at the output of comparator, so that your output voltage will not exceed 1.7V. 

    Best,

    Raymond

  • 0 in reply to Michael Steffes
    Intellectual 470 points

    Thanks for the quick reply Micheal.

  • 0 in reply to Thomas Kuehl
    Intellectual 470 points

    Thank you Thomas will surely look into this option.

    Please recommend a high slew rate opamp to be used as a non inverting Amplifier, to build gain.

    Regards

    Narendra

  • 0 in reply to Raymond Zhang1
    Intellectual 470 points

    Thank you Raymond will surely look into this option.

    Please recommend a high slew rate opamp to be used as a non inverting Amplifier, to build gain.

    Regards

    Narendra

  • 0 in reply to Narendra S10
    TI__Guru* 93105 points

    Hello Narendra,

    The OPA350/OPA2350 is our highest slew rate, low-voltage precision op amp so I can't provide another recommendation from our product line. Please have a look at TI's High-Speed op amps products. They have very high speed op amps having very high slew rate. You can see what is available at:

    The High-Speed amplifiers are supported by a different TI e2e forum. It is best to contact them regarding any questions you may have regarding their products.

    Regards, Thomas

    Precision Amplifiers Applications Engineering