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TLV9152: TLV9152 slew rate doesn't meet spec?

Farley Xu
Prodigy 10 points
Part Number: TLV9152
Other Parts Discussed in Thread: OPA2197, OPA2991, TLV9162

Hi,

I was using TLV9152 for a 1Meg bandwidth current sensing application. Below is the part of circuit I found problematic.

I tested the circuit with a signal generator，inputing 600KHz 270mVpp sine wave, the output is a sawtooth wave, showing a slew rate of 552mV/uS. Which is far below the specified 21V/us. 

The output gets sinasoidal when reducing the input voltage or frequency .

Where may go wrong with this?

  • 0
    TI__Genius 11620 points

    Hi Farley, 

    Welcome to E2E! :) 

    When measuring slew rate, the input signal would need to be a large signal step response (around 1V), so in this case, the rate of change of the output in this simulation cannot be compared to the datasheet specification. Also, the datasheet specification is specified for unity gain with a load capacitor of 20pF. Any deviation from this test condition will change your typical slew rate. 

    I set up your application in TINA to see if could mimic a similar waveform and I got a different result: 

    Did you perform your simulation using our TLV9152 simulation model downloaded from TI.com? Also, did you simulate with any load on the output? 

    Please let me know if you have any questions.
    Thank you!

    Best Regards,
    Ashley

  • 0 in reply to Ashley Kang
    Prodigy 10 points

    Hi Ashley,

    Thank you for your reply!

    Sorry I didn't make myself clear.I was not simulating the circuit,but testing with real parts.
    The load is not capacitive,and I tested the circuit with and without the load and got same results.
    I was not intentially "measuring" the slew rate, but it just seems to me the distortion is related to some slew rate issue.

    I have replaced TLV9152 with a ADI part ADA4661 and got much better result ,It has this sawtooth distortion at around 500KHz 1Vpp output. The slop is 2V/us, which is same as its specified slew rate.
    But still this is not good for my application,I need a output swing of around 2Vpp， >1MHz bandwidth.

    I have purchased some OPA2197 and OPA2991 for a try, but it will be great to solve the issue with TLV9152 for cost reasons.

    Best Regards,
    Farley

  • 0 in reply to Farley Xu
    TI__Genius 11620 points

    Hi Farley,

    Apologies on the misunderstanding! Thank you for the clarification. 

    What is most likely happening is that due to the small signal on the input, the TLV9152 is unable to slew boost properly and performing in the natural slew rate, which is why you are seeing a much slower response and the "sawtooth distortion" output. Please see the following apps note on slew rate and slew rate boost: Ramping Up on Slew Rate

    There are a few solutions for this: 

    1. Increase VID to induce slew boost using the TLV9152. The natural slew of the TLV9152 is too slow for the given input signal, so changing the input signal will help to improve the output distortion. 
    2. Switch to the TLV9162, a higher bandwidth device. The natural slew of the TLV9162 is faster and would expect to see improved performance. 

    Please let me know if you have any questions.
    Thank you!

    Best Regards,
    Ashley