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OPA2189: CMRR, PSRR and output swing

tobias kosub
Prodigy 150 points
Part Number: OPA2189
Other Parts Discussed in Thread: OPA2192, , OPA189

Hi,

I am afraid that there are some conflicting specs with respect to CMRR, PSRR and output swing in the OPAx189 datasheet.

1) Fig. 14 states CMRR and PSRR in the ~140 dB ballpark. Yet Figs. 15&16 and several passages in the text mention much higher values. So what is correct?

2) Fig. 36 says that the 30Vpp max frequency is around 10 kHz. However, the specs say it has 20 V/µs slew rate. At such slew rate, I would expect something like max 200 kHz at 30Vpp. E.g. the OPA2192 (similar amp) does show indeed 200kHz at 30Vpp at a slew rate of 20 V/µs. I need to hit at least 100 kHz at 30Vpp. Is this possible with the OPA2189 ? If not, why not ?

regards,

  • 0
    TI__Guru* 93105 points

    Hello Tobias,

    1) Fig. 14 states CMRR and PSRR in the ~140 dB ballpark. Yet Figs. 15&16 and several passages in the text mention much higher values. So what is correct?

    Note these are "Typical Characteristics" curves. Figure 14 is CMRR and PSRR vs Frequency are ac tests, while Figure 15 and 16 are CMRR and PSRR vs temperature which are dc tests. These measurements were made on different platforms and the resolution is different for the two of them. Resolving the difference between 160 db (10 nV/V) and 140 dB (100 nV/V) is in the realm of the limits of practical measurement capability. 

    Also, CMRR is a function of supply voltage-see below:

    It is best to use the CMRR and PSRR information provided in the OPA2189 Electrical Characteristics table. The performances listed in that table are what TI assures.

    2) Fig. 36 says that the 30Vpp max frequency is around 10 kHz. However, the specs say it has 20 V/µs slew rate. At such slew rate, I would expect something like max 200 kHz at 30Vpp. E.g. the OPA2192 (similar amp) does show indeed 200kHz at 30Vpp at a slew rate of 20 V/µs. I need to hit at least 100 kHz at 30Vpp. Is this possible with the OPA2189 ? If not, why not ?

    The OPA2189 uses a technique referred to as "slew boost" to attain the 20 V/us slew rate. However, in portions of the output slew range the slew rate drops down to the lower, natural slew rate of the op amp. Figure 36 is based on the lower slew rate. Here is a recent e2e post where I discussed the subject of slew boost:

    The benefit that the OPA2189 slew boost provides is near the zero crossing where dv/dt maximum such as with a sine wave the slew boost is active. However, where the sine wave dv/dt is much slower such as where the peak is approached the slew boost backs off. In that region the natural slew is sufficient to follow the waveform. You should be able to follow the a 100 kHz, 15 Vpk waveform, SR = 2 pi f Vp = (6.28)(1e5)(15) = 9.42 V/us, with the OPA2189.

    Here is a link to information regarding slew boost. See slides 10 and 11:

    https://training.ti.com/system/files/docs/1221%20-%20Slew%20Rate%201%20-%20slides.pdf

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 150 points

    Dear Thomas,

    thanks for your replies. After reading about the slew boost, I consider that the OPA189 is not suited to output a 100kHz +/-10Vp signal when linearity is critical.