7 Detailed Description

7.1 Overview

The PGA849 is a monolithic, high-voltage, precision programmable-gain instrumentation amplifier. The PGA849

combines a high-speed current-feedback input stage with an internally matched gain resistor network, followed

by a four-resistor, difference amplifier output stage. Eight pre-programmed binary gains are selectable using

gain-select pins A0, A1, A2. Gains range from 0.125V/V to 16V/V, discussed in greater detail in Section 7.3.1.

A functional block diagram for the PGA849 is shown in the next section. The differential input voltage is fed

into a pair of matched, high-impedance input, current-feedback amplifiers. An integrated precision-matched gain

resistor network is used to amplify the differential input voltage. An output difference amplifier, A3, rejects the

input common-mode component and refers the output signal to the voltage level set by the REF pin.

The PGA849 output amplifier bandwidth is optimized to drive high-performance analog-to-digital converters

(ADCs) with sampling rates up to 1MSPS, without the need for an additional ADC driver. The output amplifier

uses a separate power supply that is independent of the input-stage power supply. When driving an ADC, use

a low-impedance connection from LVDD and LVSS to the ADC power supplies. This configuration protects the

ADC inputs from damage due to inadvertent overvoltage conditions.

7.2 Functional Block Diagram

+

–

+

–

5k

5k

5k

5k

A<2:0>

DGND

IN–

IN+

DGND

VS+

A1

A2

A3

OUT

LVSS

LVDD

LVSS

LVDD

REF

DA_IN–

DA_IN+

VS+

VS−

LVDD

LVSS

VS+

VS−

VS+

VS−

VS+

VS−

VS+

VS−

VS+

VS−

+

–

VS+

VS−

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PGA849

SBOSAG3A – MARCH 2024 – REVISED DECEMBER 2024

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Product Folder Links: PGA849