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TLV9062: Low output voltage

Ivy Jin
Intellectual 2345 points
Part Number: TLV9062

Hi team,

My customer is evaluating TLV9062IDR in their product and met below issue now, could you please give some comments and suggestions?

The capacitive load drive capability shown on the datasheet of the TLV9062IDR is 100pF,  but when the actual output capacitance is 100pF, the output voltage is incorrect.

Normal theoretical calculation output voltage should be, from 1.07V to 1.27V, frequency 140KHZ, duty cycle approx. 0.8, increase slope 3.5*10^4 V/s.
Actual trapezoidal current: From 11.4A to 13.1A, frequency 140KHZ, duty cycle approx. 0.8, ramp up 0.296A/us.
Sample resistance value is 5mΩ, operational gain is 22, C482 capacitance is 220PF, C478 capacitance is 220PF.

The voltage of the sample resistance (i.e. the discharge input voltage) is increased from 57mV to 65.5mV at a frequency of 140KHZ, duty cycle approx. 0.8, ramp up 1487V/s, The actual output voltage is low.

The TLV9062 schematic is as follows: Gain: 22, C482 capacitance: 220PF, C478 capacitance: 220PF
After removing capacitance C482 in parallel with the negative feedback resistor, or reducing the capacitance to 20pF, the output voltage of TLV9062 is normal.

Thank you.

Regards,

Ivy

  • 0
    Guru 140200 points

    Hi Ivy,

    I would remove C477 and C479. They erode the phase margin and destabilize the OPAmp. If you need additional low pass filtering of input signal because the input signal is too fast for the OPAmp, then add passive low pass filtering in front of R512 and R513. Two identical RC-low pass filters will do. R512 and R513 may be splitted for this purpose.

    Kai

  • 0 in reply to kai klaas69
    TI__Mastermind 20770 points

    Hi Kai,

    I think you mean R542 and R543? 

    Hi Ivy,

    Can you provide us what the output signal is considered ideal? 

    I suspect that this is actually a filtering issue rather than the op amp not being able to drive the capacitive load based on the information provided. 

    Best Regards, 

    Robert Clifton 

  • +1
    Guru 140200 points

    Hi Ivy,

    after running some simulations I tend to aggree with Robert: What you see is more a low pass filtering issue because you do too much low pass filtering. See the performance when changing C1 from 220p to 22p:

    And compare it with the performance of an ideal (and infinitely fast !) OPamp:

    Even the ideal OPAmp cannot produce much sharper edges with your low pass filtering.

    A remedy is to remove or at least heavily decrease the low pass filtering time constants set by C1 and C2. Also, remove C3 and C4 all the way since they are counterproductive and only degrade the stability. Then, you get this:

    Sharper edges cannot be achieved with the TLV9062 because of its limited speed. Only a much faster OPAmp can do sharper edges. See the performance of ideal OPAmp again:

    ivy_tlv9062.TSC

    Kai

  • 0 in reply to kai klaas69
    TI__Intellectual 2345 points

    Thanks Kai and Robert,

    I will feedback to the customer and ask them to re-test as your suggestions.

    Many thanks!

    Regards,

    Ivy