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AFE031: Documentation conflict regarding coupling capacitor selection

John French1
Prodigy 30 points
Part Number: AFE031

Hello,

I am seeing conflicting information within separate documents as well as the single datasheet for this AFE031 part.

1) The document below (updated 11/2011), at the bottom of page 6 (equation 2) says the calculation should be made using 2kohm

http://www.ti.com/lit/an/sboa130a/sboa130a.pdf

2) Meanwhile the actual datasheet for the part has 2 separate equations:

a) On page 24, it says to use 20kohm in the calculation

b) On page 25, in note 1 of figure 26 it says to use 22kohm in the calculation.

http://www.ti.com/lit/ds/symlink/afe031.pdf

Can you clarify this for me?

  • 0
    TI__Guru* 77521 points

    Hi John,

    I see that there is typo here (inconsistency in the datasheet). Yes, please use 22kOhm to calculate the capacitor value, shown in red circuit. 22kOhm is the input impedance of PA_IN, which it is part of High Pass Filter. The transmission frequency is approx. at 150kHz range for AFE031, and we do not want get Higher High Pass Filter, f = 1/(2*pi*22kHz*C).

    20kOhm in Equation 2 (on p. 24) is correct at PA_ISET pin (pin46),  which the data is based on Figure 20 of the AFE031 datasheet. The current limiting resistor, Rset, is used to protect the Power Amplifier, so it will not exceed the over current conditions. 

    If you have any other questions, please let us know. 

    Best,

    Raymond