CDB5534U

DS289DB6

3

1. HARDWARE

1.1

Introduction

The CDB5534U evaluation board provides a quick means of evaluating the CS5534 Analog-to-Digital

Converter (ADC). The CS5534 is a highly integrated

∆Σ ADC which uses charge-balance techniques to

achieve 24-bit performance. The CS5534 includes a very low noise chopper-stabilized instrumentation

amplifier (6 nV/sqrt(Hz) @ 0.1 Hz) with selectable gains of 1×, 2×, 4×, 8×, 16×, 32×, and 64×. This ADC

also includes a fourth order

∆Σ modulator followed by a digital filter which provides twenty selectable out-

put word rates of 6.25 Hz, 7.5 Hz, 12.5 Hz, 15 Hz, 25 Hz, 30 Hz, 50 Hz, 60 Hz, 100 Hz, 120 Hz, 200 Hz,

240 Hz, 400 Hz, 480 Hz, 800 Hz, 960 Hz, 1.6 kHz, 1.92 kHz, 3.2 kHz and 3.84 kHz (XIN = 4.9152 MHz).

The CDB5534U is shipped with a CS5534 device soldered at U2. However, the CS5531, CS5532, or

CS5533 can be soldered in this same location. The CDB5534U software supports all four devices.

1.2

Evaluation Board Overview

The CDB5534U evaluation board is partitioned into two main sections: analog and digital. The analog sec-

tion consists of the CS5534 and a precision voltage reference. The digital section consists of the micro-

controller, the reset circuitry, and the USB interface. The board also has power supply connections which

accommodate all of the various supply options of the CS5534.

The evaluation board’s analog section operates from either a single +5 V, dual ±2.5 V, or dual ±3 V power

accomplish this, the board comes equipped with a microcontroller and a USB cable which physically in-

terfaces the evaluation board to the PC. The software provides easy access to the internal registers of the

CS5534, and provides a means to display and evaluate the performance of the ADC in the time domain

or the frequency domain.

1.2.1

Analog Section

The CS5534 is a high precision

∆Σ converter designed to accurately measure up to four fully-differential

analog voltage inputs while operating from a 4.9152 MHz crystal.

The evaluation board provides separate screw terminals to connect signals to each of the four input chan-

nels. The input screw terminals are labeled as AIN1 through AIN4, which correspond to physical input

channels 1 through 4 respectively. A simple RC network on each channel filters the sensor’s output to

reduce any interference picked up by the input leads. The 3 dB corner of the filter is approximately 52 kHz

differential and 56 kHz common mode. Figure 1 illustrates the schematic of the analog section.

The evaluation board provides three voltage reference options for VREF+ and VREF-. The three refer-

ence options for VREF+ include: VA+, the on-board LT1019 voltage reference, and external input (J12).

Table 1 illustrates the options available. With the J17 jumper in position VA+, the reference is supplied by

the VA+ analog supply. With the J17 jumper in position LT1019, the LT1019 provides a +2.5 V reference

(the LT1019 was chosen for its low drift, typically 5ppm/°C). By setting the J17 jumper to position VREF+,

the user can supply an external voltage reference to J12’s VREF+ input.

The three reference options for VREF- include: VA-, GND, and external input (J12). Table 2 illustrates the

options available. With the J18 jumper in position VA-, the reference is supplied by the VA- analog supply.

With the J18 jumper in position GND, the VREF- pin is connected to the board ground. By setting the J18

jumper to position VREF-, the user can supply an external voltage reference to J12’s VREF- input.