TLV9002: TLV9002 PSRR spec question

Mason,

I could not find any reference to 'PSRR±' in the data sheet. 

If you mean PSRR+ and PSRR-  then that means the AC supply voltage was applied to V+ or V- respectively. 

Hi Mason,

it's pretty well explained here:

Kai

Hi Ronald,

So i'm wondering where the AC supply come from? I mean in the AMP, Vsupply always DC contains some ripple, why we need to analyse AC supply?

Thanks.

Best regards

Mason Liu

Hi Mason,

not all applications power the OPamp with a voltage regulator. So, there can be lots of 120Hz rectifier ripple with their far reaching harmonics on the supply line. Or think of heavy loads, which draw big current spikes. Or think of automative applications with the noisy car battery voltage containig lots of glitches and dips. According to monsieur Fourier these short lasting dips and glitches produce a wide spectrum of frequencies.

But even a voltage regulator can be problematic, because it generates wide band noise and has a very limited ripple rejection and a poor output impedance at higher frequencies.

Keep in mind that power supply noise, after being partially suppressed by the power supply rejection of OPAmp, will appear at the input stage and is amplified by the installed gain, very similar to what happens to the input offset voltage of OPAmp, but with the difference that it contains a wide spectrum of frequencies. So, a high gain AC pre-amplifier might need a very high power-supply-rejection-ratio at the same time.

Kai

Mason,

Is this the chart in question?

The AC supply is mandated by the chart title, PSRR vs FREQUENCY

Hi Ronald,

So, can i say that PSRR+/PSRR- shows how PSRR change with the frequency? 

And PSRR in the table is the spec i should pay more attention when choose AMPs?

Thanks.

Best regards

Mason

Hi Mason,

yes, PSRR+ and PSRR- are showing the PSRR versus frequency. And the PSRR in the table is just the DC value of PSRR. Read again my link to see how it is determined.

While the PSRR+ and PSRR- graphs in the datasheet are usually only showing typicals, for the PSRR value in the table also a maximum value is specified.

What data you should pay more attention to depends on your application. But you cannot simply say that the one is more important than the other.

Kai