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# TLV171-Q1: Closed-loop gain for voltage follower circuit

Part Number: TLV171-Q1

Hi team,

We will use TLV171-Q1 as voltage follower circuit.

We require a gain error of ±0.01dB with up to 30kHz on this device.

I think that probably it is no problem by looking at the figure 12. Closed-Loop Gain vs Frequency.

Does it fit within ±0.01dB in 30kHz?

The attenuation at 8 MHz appears to be about -7 dB, but can you see the exact value?

Should it be considered that 8 MHz or more attenuates at 40dB/dec?

Best regards,

Tomoaki Yoshida

• Hi Yoshida-san,

At 30kHz, the open loop gain of the op amp is around 45dB which is a gain of 177.83 V/V. This can be seen in figure 10 of the datasheet. In the voltage follower configuration, your gain is 0dB or 1 V/V. Starting from equation 15 in this app note (www.ti.com/.../slyt374.pdf), the gain error in this scenario is equal to:

Gain Error @ 30kHz = (1-[Aol/(1+beta*Aol)]/(Ideal Acl))*100 = (1-[177.83/(1+177.83)]/1)*100 = 0.559% gain error at 30kHz.

Your requirement of ±0.01dB translates to 0.1% error at 30kHz, which the math above shows that it does not meet. This requirement seems like a very strict one to meet, can you describe your application in a little more detail? Do you have a high precision way to measure this error? You're going to need a source capable of providing better than 0.1% variation on the input signal.

The best way to handle such a requirement, regardless of the device chosen would be to implement a two point calibration using a precision DAC. The values given the Aol vs Freq curve in the datasheet are given as typical values and can swing 20% based on process and temperature, further adding to the difficulty of meeting that spec.

Let me know your thoughts on this topic and we can discuss further.

Thank you,
Paul