Part Number: THS4541
For enhancement of SNR I used LM7705 to drive VSS of THS4541 pin,, as TI recommended,
Bias on datasheet of this switching capacitor regulator, the noise will increase at the out put of regulator as the output current increase,
the maximum current that this device can provide is 26mA
cause I don't know how much current is required in THS4541 VSS pin ,I am not sure this regulator could be able to drive 4 op-amp or no?
Thank you all
So you are trying to supply 4-THS4551 with a single LM7705?
1. noise on the regulator output will be filtered by the caps and further rejected by the very high -PSRR of the THS4541
2. I think the THS4541 is about 11mA, so maybe you can supply 2 of them per LM7705
3. It is not so much to improve noise but swing to ground HD performance to supply a -0.23V on the negative supply -if you don't need to swing to ground (most ADC driver apps do not), then you may not need this.
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In reply to Michael Steffes:
the datasheet of THS4541 mentioned that the question current of op amp is about 11mA but has not specified how much is related to positive rail and how much is for negative rail.
what is important for me is negative rail current .
I used capacitor and ferrit bead at the out put but still there is noise which is not acceptable .
In reply to VAHID FARSI:
The currents should be equal, 11mA in on the +Vcc and 11mA out on the -Vcc.
Yes, if the -Vcc has noise on it that is a concern, but how much is getting through to the differential output pins as a differential signal related to that switching supply.
I am not sure both negative and positive supply have same current , how can I make sure?
If you can hook the board up to a bench supply that would be the easiest method. Otherwise you can try and measure a voltage drop across a small series resistor in the supply.
Jacob Freet High Speed Amplifiers
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