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The RefMux Setting and the AGndBypass Option in PSoC® Designer™ - KBA86944

The RefMux Setting and the AGndBypass Option in PSoC® Designer™ - KBA86944

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Question: What is the RefMux setting and what is the AGndBypass option in PSoC® Designer™? What is their significance?



RefMux setting: This parameter enables the user to select the analog ground and the input range of the analog blocks. See Figure 1.

The reference generator generates three voltages: AGND (the analog ground for all the analog blocks), RefHi, and RefLo (which sets the range for the analog resources). These voltages are derived from VDD, a 1.3 V bandgap reference generator, or external voltages connected to P2[4] and P2[6]. For example, if VDD = 5.0 V and the RefMux is set to VDD/2 ± BandGap, this sets AGND to 2.5 V, RefHi to 3.8 V, and RefLo to 1.2 V. This means that the allowed input range for the analog resources is from 1.2 V to 3.8 V.

Figure 1. Analog Ground Bypass

For detailed information about the RefMux setting, see AN2219 - PSoC® 1 Selecting Analog Ground and Reference and Chapter 21- Analog Reference in the PSoC Technical Reference Manual.

AGndBypass option: When AGND Bypass is set to Enabled, pin P2[4] is in High-Z Analog mode. An external capacitor connected between P2[4] and VSS reduces the noise at the AGND input. Typical values for the bypass capacitor are 0.01 µF and should not exceed 0.1 µF.