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[THS4521] Stability and Offset

Dominique Henry
Prodigy 20 points

Other Parts Discussed in Thread: THS4521, TINA-TI

Hello,

I am currently working on an integrator device using a THS4521 amplifier in a differential input/output configuration.
The amplifier is powered with 0/+3,3V supply and an offset of 1.65V. (see attached files)

Despite Tina-Ti gave simulation results I expected, real experiment shows that the amplifier is unstable for an offset range from 0 to 2.8V (signal oscillations). Expected characteristics are obtained when offset>2.8V.

Do you have an idea of the origin this instability problem? The problem still occurs when I remove load capacitors or decrease the closed-loop gain.

Regards,

Dominique Henry

LowPass_TiForum.tsc
  • 0
    TI__Mastermind 22825 points

    Hello Dominique,

    I'm not an expert with the THS4521 but I think your instability might be related to the 4nF cap load you have on each output. The datasheet recommends a series output resistor (Figure 66) when driving any cap load greater than 1pF. With this large a cap load, I think a few ohms might be enough. Have you tried a series isolation resistor?

    Regards,

    Hooman

  • 0 in reply to Hooman Hashemi
    Prodigy 20 points

    Thanks for your response.

    You are right. The problem is solved. By putting 50 Ohms serial resistors at the output of the amplifier, there is no more instability problem. Noise and signal fluctuation were also generated by the Vocm pin so I put a capacitor from Vocm to the ground.

    Regards,

    Dominique