2 Hardware

This EVM provides access to the features and measures the performance of the PGA854 device. By default, the PGA854EVM programmable gain amplifier is configured to a gain of 0.5V/V. The evaluation board provides jumpers J10 (A2), J11 (A1), and J12 (A0) to set the PGA854 gain.

The device uses two sets of voltage supplies: input stage and output stage. The output-stage power supplies are decoupled from the input stage to limit the PGA854 output-swing voltage level protecting the ADC or downstream device against overdrive damage. The input-stage supplies, VS+ and VS–, are accessible using connector J13. The output-stage supplies, LVDD+ and LVSS–, are accessible using connector J14. Selectable jumpers J9 and J16 set the output-stage supply voltage level equal to the input-stage supplies (default), or to external voltages using connector J14.

The PGA854 incorporates features that simplify interfacing to a fully differential ADC. The output common-mode voltage can be independently set by using the VOCM pin. If the VOCM connector is not driven, the output common-mode voltage defaults to the PGA854 output stage mid-supply value. The PGA854EVM allows access to the FDA_IN– and FDA_IN+ pins with optional capacitors C4 and C14. These capacitors are in parallel with the PGA854 output-stage internal-feedback resistors to implement noise filtering. Figure 2-1 displays a simplified block diagram of the PGA854EVM. For a full schematic of the PGA854EVM, see Figure 3-6.

Figure 2-1 PGA854EVM Simplified Schematic