Texas Instruments ADS794xEVM Manual de usuario

User's Guide

SBAU194–August 2011

ADS794xEVM and ADS794xEVM-PDK

ADS794xEVM-PDK

This user's guide describes the characteristics, operation, and use of the ADS794xEVM by itself and as

part of the ADS794xEVM-PDK kit. These evaluation modules (EVMs) allow evaluation of all aspects of

either the ADS7946 or ADS7945 devices (ADS794x). Both devices are 14-bit, dual-channel,

ultralow-power, differential successive-approximation-register (SAR) analog-to-digital converters (ADCs)

with a maximum throughput rate of 2 MSPS. The ADS7945 offers fully-differential input voltages while the

pseudo-differential inputs of the ADS7946 offer single-ended input voltages with small common-mode

noise-cancelling capabilities. Complete circuit descriptions, schematic diagrams, and bill of materials are

included in this document.

The following related documents are available through the Texas Instruments web site at

http://www.ti.com.

Related Documentation

Device Literature Number

ADS7945 SBAS539

ADS7946

OPA350 SBOS099C

OPA836 SLOS712B

REF5040 SBOS410E

SN74LVC2G74 SCES203M

ADCPro is a trademark of Texas Instruments.

Microsoft, Windows are registered trademarks of Microsoft Corporation.

SPI is a trademark of Motorola, Inc.

I2C is a trademark of NXP Semiconductors.

All other trademarks are the property of their respective owners.

SBAU194–August 2011 ADS794xEVM and ADS794xEVM-PDK

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Contents

1 EVM Overview ............................................................................................................... 3

2 Analog Interface ............................................................................................................. 4

3 Digital Interface .............................................................................................................. 7

4 Power Supplies .............................................................................................................. 8

5 EVM Operation .............................................................................................................. 9

6 ADS794xEVM-PDK: Software Installation ............................................................................. 10

7 ADS794xEVM-PDK Kit Operation ....................................................................................... 17

8 Bill of Materials, Schematics, and Layout .............................................................................. 20

List of Figures

1 ADS794xEVM and ADS7945 Analog Inputs ............................................................................ 5

2 ADS794xEVM and ADS7946 Analog Inputs ............................................................................ 6

3 ADS794xEVM Default Jumper Locations .............................................................................. 10

4 ADS794xEVM-PDK Plug-In Installer.................................................................................... 11

5 Completed ADS794xEVM-PDK Installer ............................................................................... 11

6 MMB0 Jumper Locations................................................................................................. 12

7 Connecting ADS794xEVM to MMB0.................................................................................... 13

8 Powering Up ADS794xEVM-PDK....................................................................................... 14

9 NI-VISA Driver Installation Prompt...................................................................................... 15

10 Loading ADS794xEVM Plug-in From ADCPro ........................................................................ 15

11 USBStyx Driver Installation Prompt..................................................................................... 16

12 ADS794xEVM Plug-in: Device Configuration Tab .................................................................... 18

13 ADCPro Test Plug-ins .................................................................................................... 19

14 ADS794xEVM PCB: Top Layer.......................................................................................... 22

15 ADS794xEVM PCB: Ground Layer ..................................................................................... 22

16 ADS794xEVM PCB: Power Layer....................................................................................... 23

17 ADS794xEVM PCB: Bottom Layer...................................................................................... 23

List of Tables

1 P2: Analog Interface Pinout (Samtec 10 x 2) ........................................................................... 4

2 SMA Analog Inputs ......................................................................................................... 4

3 P1: Serial Interface Header................................................................................................ 7

4 P3 Configuration: Power-Supply Interface Header..................................................................... 8

5 ADS794xEVM Bill of Materials .......................................................................................... 20

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EVM Overview

1 EVM Overview

1.1 Features

ADS794xEVM Features:

•Contains all support circuitry needed for the ADS7946/ADS7945 (ADS794x)

•5-V, 3.3-V, and 1.8-V logic compatible with 16-bit, 40-MHz SPI™serial interface

•Simple channel selection with a single 16-bit word command

•Serial interface header for easy connection to TI DSP-based communication systems

•Compatible with the TI Modular EVM System

•Voltage reference options: onboard REF5040 (4.096-V) reference or external reference

•Voltage reference buffering with OPA350

•Onboard OPA836 (200-MHz BW, 1-mA quiescent current) ADC input drivers

•Jumper-selectable bipolar (–VREF/2 to +VREF/2) or unipolar (0 V to VREF) input range

ADS794xEVM-PDK Features:

•Easy-to-use evaluation software for Microsoft®Windows®XP operating system PCs

•Data collection to text files

•Built-in analysis tools including scope, FFT, and histogram displays

•Complete control of board settings

•Easily expandable with new analysis plug-in tools from Texas Instruments

The ADS794xEVM-PDK is available for use with a computer. This kit combines the ADS794xEVM board

with the DSP-based MMB0 motherboard, and includes ADCPro™software for evaluation.

The MMB0 motherboard allows the ADS794xEVM to be connected to the computer via an available USB

port. This manual shows how to use the MMB0 as part of the ADS794xEVM-PDK, but does not provide

technical details about the MMB0 itself.

ADCPro is a program for collecting, recording, and analyzing data from ADC evaluation boards. It is based

on a number of plug-in programs, so it can be expanded easily with new test and data collection plug-ins.

The ADS794xEVM-PDK is controlled by a plug-in running in ADCPro. For more information about

ADCPro, see the ADCPro™Analog-to-Digital Converter Evaluation Software User's Guide (literature

number SBAU128), available for download from the TI web site.

This manual covers the operation of both the ADS794xEVM and the ADS794xEVM-PDK. Throughout this

document, the abbreviation EVM and the term evaluation module are synonymous with the ADS794xEVM.

Operation of the EVM and kit for both the ADS7946 and the ADS7945 devices is identical, unless

otherwise noted.

1.2 Introduction

The ADS794xEVM is an evaluation module built to the TI Modular EVM System specifications. It can be

connected to any modular EVM system interface card.

The ADS794xEVM is available as a stand-alone printed circuit board (PCB) or as part of the

ADS794xEVM-PDK, which includes an MMB0 motherboard and software. As a stand-alone PCB, the

ADS794xEVM is useful for prototyping designs and firmware because it offers circuitry that meets the

product data sheet specifications of either the ADS7946 or ADS7945 devices.

The ADS7945 and ADS7946 are 14-bit, 2-MSPS ADCs with fully differential and pseudo-differential

unipolar inputs, respectively. These devices operate at a 2-MSPS sample rate with a 16-clock SPI data

frame that features both outstanding dc and excellent dynamic performance. These devices also include a

two-channel input multiplexer and a low-power SAR ADC with an inherent sample-and-hold (S/H) input

stage. During normal operation at 2 MSPS, the ADS794x dissipates a mere 11.6 mW.

Note that the ADS794xEVM has no microprocessor and cannot run software. Therefore, some type of

interface is required to connect the ADS794xEVM to a computer. In the ADS794xEVM-PDK kit, the MMB0

motherboard serves as the interface between the computer and the ADS794xEVM board.

SBAU194–August 2011 ADS794xEVM and ADS794xEVM-PDK

Analog Interface

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2 Analog Interface

The ADS794xEVM is designed for easy interfacing to multiple analog sources. SMA connectors allow the

EVM to have input signals connected via coaxial cables. In addition, the Samtec connector provides a

convenient 10-pin, dual-row, header/socket combination at P2. This header/socket provides access to the

analog input pins of the ADS794x. Consult Samtec at http://www.samtec.com or call 1-800-SAMTEC-9 for

a variety of mating connector options. All analog inputs are buffered by OPA836 high-speed operational

amplifiers in order to properly drive the ADS794x ADC inputs.

Use appropriate caution when handling these pins. Table 1 summarizes the pinout for analog interface P2.

Table 1. P2: Analog Interface Pinout (Samtec 10 x 2)

Pin Number Signal Description

CH0 positive differential input for ADS7945; open if

P2.2 A0(+) / OPEN ADS7946 is installed

CH0 negative differential input for ADS7945;

P2.4 A0(–)single-ended input for ADS7946

CH1 positive differential input for ADS7945; open if

P2.10 A1(+) / OPEN ADS7946 is installed

CH1 negative differential input for ADS7945;

P2.12 A1(–)single-ended input for ADS7946

P2.1-19 (odd) GND Analog ground connections (except J1.15)

P2.6 and P2.8 GND Analog ground connections

P2.14, P2.16, and P2.18 GND Analog ground connections

Unbuffered output. VREF/4 (J6 open) or VREF/2 (J6

P2.15 VREF/4 or VREF/2 closed)

P2.20 Ext VREF External reference voltage input

Table 2 lists the SMA analog inputs.

Table 2. SMA Analog Inputs

Pin Number Signal Description

CH0 positive differential input for ADS7945; no

J10 A0(+) / No SMA SMA if ADS7946 is installed

CH0 negative differential input for ADS7945;

J11 A0(–)single-ended input for ADS7946

CH1 positive differential input for ADS7945; no

J4 A1(+) / No SMA SMA if ADS7946 is installed

CH1 negative differential input for ADS7945;

J5 A1(–)single-ended input for ADS7946

As noted in Table 1 and Table 2, there are different hardware configurations depending on the installed

converter. The ADS7945 uses two inputs per channel because of its fully differential inputs. The ADS7946

uses one input per channel for its pseudo-differential inputs.

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SMA

J10

SMA

J11

SMA

A0(+)

A1(+)

A0( )-

A1( )-

OPA836 in Inverting

Configuration

OPA836 in Inverting

Configuration

OPA836 in Inverting

Configuration

OPA836 in Inverting

Configuration

AIN1P (pin 8)

AIN1N (pin 7)

AIN0P (pin 5)

AIN0N (pin 6)

ADS7945

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Analog Interface

2.1 ADS794xEVM Analog Inputs with ADS7945 Installed

Each channel of the ADS7945 uses two OPA836 operational amplifiers to drive the fully differential inputs.

The input signals can be applied to either the SMA or P2 header connectors. These operational amplifiers

offset the input signal to use an inverting configuration with a single supply. The EVM Operation section

explains in detail how this offset is used to allow bipolar signals for the ADS7945 with jumper J6.

Figure 1 illustrates the ADS794xEVM analog inputs with the ADS7945 installed.

Figure 1. ADS794xEVM and ADS7945 Analog Inputs

SBAU194–August 2011 ADS794xEVM and ADS794xEVM-PDK

No SMA

J10

SMA

J11

No SMA

SMA

A0(+)

A1(+)

A0( )-

A1( )-

OPA836 in Inverting

Configuration

OPA836 in Inverting

Configuration

AIN1P (pin 8)

AIN1N (pin 7)

AIN0P (pin 5)

AIN0N (pin 6)

ADS7946

Open

Analog Interface

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2.2 ADS794xEVM Analog Inputs with ADS7946 Installed

Each channel of the ADS7946 uses one OPA836 to drive a single-ended input voltage. The input signals

can be applied to either the SMA or P2 header connectors. These operational amplifiers offset the input

signal to use an inverting configuration with a single supply. The EVM Operation section explains in detail

how this offset is used to allow bipolar signals for the ADS7946 with jumper J6.

Figure 2 shows the ADS794xEVM analog inputs with the ADS7946 installed.

Figure 2. ADS794xEVM and ADS7946 Analog Inputs

2.3 External Reference Input

Pin P2.20 is an analog input for an external reference voltage when J2 is in position 2-3. The source that

provides this external reference should have a voltage between 2.5 V and the analog power-supply

voltage.

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Digital Interface

3 Digital Interface

Samtec part numbers SSW-110-22-F-D-VS-K and TSM-110-01-L-DV-P provide a convenient 10-pin,

dual-row, header/socket combination at P1. This header/socket provides access to the digital control pins

of the ADC. Consult Samtec at http://www.samtec.com or call 1-800-SAMTEC-9 for a variety of mating

connector options.

Table 3 summarizes the pinouts for digital interface P1.

Table 3. P1: Serial Interface Header

Pin Number Signal Description

P1.1 CS Chip select input. Pulled high with 10-kΩresistor.

P1.3 SCLK Serial clock input

Chip select input. This pin is intended to be used by

P1.7 CS the MMB0 motherboard

P1.11 SDI or MOSI SDI or MOSI input

P1.13 SDO or MISO SDO or MISO output

Power-down input (active high). Pulled down with

P1.19 PDEN 10-kΩresistor.

P1.4, P1.10, and P1.18 GND Digital ground connections

I2C bus; used only used to program the U4

P1.16, P1.20 I2C™bus EEPROM on the EVM board

P1.2, P1.5-6, P1.8-9,

P1.12, P1.14-15, and Unused Unused

P1.17

3.1 Serial Interface (SPI)

The ADS794x ADC uses SPI serial communication in mode 0 (CPOL = 0, CPHA = 0). Because the serial

clock (SCLK) frequency can be as fast as 40 MHz, the ADS794xEVM offers 47-Ωresistors between the

SPI signals and P1 to aid with signal integrity. Typically, in high-speed SPI communication, fast signal

edges can cause overshoot; these 47-Ωresistors slow down the signal edges in order to minimize signal

overshoot.

3.2 ADS794x Channel Select as SDI (MISO)

The ADS794x ADC offers direct control over the internal multiplexer using pin 11. The ADS794xEVM uses

a flip-flop (see U9 in the attached schematic) to convert this pin into a typical SPI SDI (MOSI) pin. This

architecture takes advantage of the SPI full-duplex data transmission sequence to control channel

selection at the same time conversion data are acquired. The digital word 0x000 can be used to select

channel 0, and the word 0xFFFF can be used to select channel 1.

3.3 I2C Bus for Onboard EEPROM

The ADS794xEVM has an I2C bus to communicate with the onboard EEPROM that records the board

name and assembly date. It is not used in any form by the ADS794x converter.

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Power Supplies

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4 Power Supplies

P3 is the power-supply input connector. Table 4 lists the configuration details for P3.

Table 4. P3 Configuration: Power-Supply Interface Header

Pin Number Pin Name Function Required

P3.3 +5VA 5-V analog supply Yes

P3.5 GND Digital ground input Yes

P3.6 GND Analog ground input Yes

P3.7 +1.8VD 1.8-V digital supply Yes/Optional

P3.9 +3.3VD 3.3-V digital supply Yes/Optional

P3.10 +5VD 5-V digital supply Yes/Optional

P3.1-2, P3.4, and Unused Unused No

P3.7-8

4.1 Analog Power Options

The ADS794xEVM board is designed to work with a 5-V analog power supply connected to P3.3.

4.2 Digital Power Options

The ADS794xEVM uses a jumper in J3 to connect the digital power supply to either +3.3 VD (P3.10) or +5

VD (P3.9). J3 in position 1-2 connects the digital power supply to +5 VD; position 2-3 connects the digital

power supply to +3.3 VD. Without a jumper in J3, the digital power supply can be connected to +1.8

VD(P3.7) with a jumper wire to pin J3.2. The jumper in J3 must always be in position 2-3 (+3.3 VD) while

using the MMB0 with the EVM.

4.3 Reference Voltages

The ADS794xEVM uses a jumper in J2 to select between the internal (REF5040) and external voltage

reference sources. J2 in position 1-2 selects the internal reference; position 2-3 selects the external

reference. The selected reference is cleaned with a RC filter and buffered with a OPA350 operational

amplifier.

CAUTION

Digital supply and reference voltage must be at or below the analog supply

voltage at all times.

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EVM Operation

5 EVM Operation

This section provides information on the analog input, digital control, and general operating conditions of

the ADS794xEVM without the MMB0 motherboard. Software operation is presented in Section 7.

5.1 Analog Input

The ADS794xEVM offers three different analog input modes, selectable with jumper J6 and the type of

input signal. Note that the ADS794x converter by itself only allows dc-coupled unipolar signals. The two

additional input modes are available because OPA836 operational amplifiers drive the analog inputs. It is

preferable for external signal drivers or filters to have low output impedance to reduce gain errors.

Mode 1: DC-Coupled Unipolar Inputs (J6 Closed)

DC-coupled unipolar signals are typically produced by single-supply signal drivers. To allow dc-coupled

unipolar signals, J6 should be closed. This mode allows an input signal range from 0 V to VREF for all EVM

analog inputs. In this mode, the voltage read at the ADC is equal to (VREF –VIN).

Mode 2: DC-Coupled Bipolar Inputs (J6 Open)

DC-coupled bipolar signals are typically produced by dual-supply signal drivers. To allow dc-coupled

bipolar signals, J6 should be open. This mode allows an input signal range from –VREF/2 to +VREF/2 for all

EVM analog inputs. In this mode, the voltage read at the ADC is equal to (VREF/2 –VIN).

Mode 3: AC-Coupled Inputs (J6 Closed)

AC-coupled signals are typically produced by high-pass filters. To allow ac-coupled bipolar signals, J6

should be closed. This mode allows an input signal range from –VREF/2 to +VREF/2 for all EVM analog

inputs. In this mode, the voltage read at the ADC is equal to (VREF/2 –VIN).

5.2 Digital Control

The digital control signals can be applied directly to the P1 header (top or bottom side). The modular

ADS794xEVM can also be connected directly to a DSP or microcontroller interface board, such as the

5-6K Interface or HPA-MCU Interface boards available from Texas Instruments, or the MMB0 if purchased

as part of the ADS794xEVM-PDK. For a list of compatible interface and/or accessory boards for the EVM

or the ADS794x, see the relevant product folder on the TI web site.

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ADS794xEVM-PDK: Software Installation

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5.3 Default Jumper Settings

Figure 3 shows the jumper locations on the EVM board and the respective factory default conditions for

each.

Figure 3. ADS794xEVM Default Jumper Locations

There are four jumpers on the ADS794xEVM board. These jumpers are used to set the CS signal entry

pin (J1), select the digital logic level (J3), select the reference (J2), and to establish the input signal range

type (J6). The default parameters are:

•The CS signal entry pin is P1.7 (J1: 2-3).

•The logic level is 3.3 V (J3: 2-3).

•The onboard 4.096 V is selected as the reference voltage (J1: 1-2).

•Analog input range is 0 V to VREF (4.096 V) with dc-coupled signals (J6: closed)

6 ADS794xEVM-PDK: Software Installation

This section presents the steps required to the install the software. Section 7 explains how to operate the

software to acquire data.

Complete the following steps to install the software:

Step 1. Install the ADCPro software (if not already installed) on a PC.

Step 2. Install the ADS794xEVM-PDK EVM plug-in software.

Step 3. Set up the ADS794xEVM-PDK hardware.

Step 4. Power up the ADS794xEVM-PDK.

Step 5. Connect the ADS794xEVM-PDK to the computer with a USB cable.

Step 6. Complete the USB driver installation process.

Each task is described in the subsequent sections of this document.

10 ADS794xEVM and ADS794xEVM-PDK SBAU194–August 2011

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