National Semiconductor ADC121C021 Manual de usuario

NOTE: The Evaluation Board is shipped with the Alert Option of the ADC. To

evaluate the Address Option, please order samples from www.national.com.

National Semiconductor

January 3, 2008

Rev – 1.1/CC

RoHS Compliant

Evaluation Board User's Guide

C-Compatible, 12-Bit, 10-Bit, or 8-Bit

Analog-to-Digital Converter (ADC) with Alert Function

12-bit 10-bit 8-bit

ALERT Option

ADC121C021 ADC101C021 ADC081C021

ADDRESS Option

ADC121C027 ADC101C027 ADC081C027

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Table of Contents

1.0 Introduction ............................................................................................................................3

2.0 Board Assembly .....................................................................................................................4

3.0 Quick Start .............................................................................................................................5

3.1 Stand Alone Mode.....................................................................................................5

3.2 Computer Mode ........................................................................................................5

4.0 Functional Description............................................................................................................6

4.1 Jumper Settings ........................................................................................................6

4.2 Analog Input Signal ...................................................................................................7

4.3 ADC Reference Circuitry...........................................................................................7

4.4 I

C Interface ..............................................................................................................7

4.5 Alert Function ............................................................................................................7

4.6 Automatic Conversion Mode .....................................................................................8

4.7 Power Supply Connections .......................................................................................8

5.0 Software Operation and Settings ...........................................................................................8

5.1 Software Quick Start .................................................................................................8

5.2 Data Analysis ............................................................................................................9

5.3 Register Control ........................................................................................................10

5.4 Troubleshooting WaveVision ....................................................................................11

6.0 Evaluation Board Specifications ............................................................................................12

7.0 Test Points, Connectors, and Jumpers..................................................................................12

8.0 Hardware Schematic..............................................................................................................13

9.0 Evaluation Board Layers ........................................................................................................14

10.0 Evaluation Board Bill of Materials ........................................................................................15

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1.0 Introduction

This Design Kit (consisting of the ADC Evaluation

Board and this User's Guide) is designed to ease

evaluation and design-in of National

Semiconductor’s ADC121C021 family of Analog-

to-Digital Converters. The ADCs can operate at

speeds up to 188.9 kSPS. The converter features

an I

C interface and an Alert function. This User’s

Guide supports all three resolutions and both

package options of the ADC121C021 ADC family.

All the devices in the family (ADC121C021,

ADC121C027, ADC101C021, ADC101C027,

ADC081C021, and ADC081C027) will be referred

to as the ADC121C021 in this document. The

ADCXX1C021 options offer an ALERT output pin,

whereas, the ADCXX1C027 offers an address

selection pin. The board comes stuffed with the

ALERT option (ADCXX1C021). To evaluate the

Address Option (ADCXX1C027) with this board,

please go to www.national.com and order

samples. Use care when de-soldering the ADC to

ensure the pads of U3 are not damaged.

The evaluation board can be used in either of two

modes. In Stand Alone, suitable test equipment

such as a logic analyzer with a pattern generator

can be used with the board to evaluate the

ADC121C021’s performance.

In the Computer mode, data capture and

evaluation are simplified by connecting the

evaluation board to National Semiconductor's

WaveVision 4 Data Capture Board (order number

WAVEVSN BRD 4.1 or higher) which connects to

a personal computer through a USB port and runs

WaveVision 4 software revision 4.4 or higher.

The latest version of the WaveVision 4 software

should be downloaded from the web at

http://www.national.com/adc.

Note: WaveVision software version 4.4 or higher

is required to evaluate this part with the WV4

Evaluation System.

The WaveVision 4 software operates under

Microsoft Windows. The signal at the analog

input is digitized, captured, and displayed on a PC

monitor in the time and frequency domains.

The software will perform an FFT on the captured

data upon command. This FFT plot shows the

dynamic performance in the form of SNR, SINAD,

THD, SFDR, and ENOB. A software histogram of

the captured data is also available. WaveVision

also provides control of the ADC’s internal

registers through the WaveVision4 software.

The signal at analog input J2 is digitized by U3,

the ADC121C021.

Figure 1: Component Locations

JP1: INPUT

SELECT

JP5: VA

SELECT

J2: INPUT

JP2: I

C PULL-UP

Enable

J1: WV4S

Connector

JP7: 4.1V

REF Enable

U3: ADC

[ADC121C021]

U5: REF

[LM4050-4.1]

U2: AMP

[LMP7731]

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2.0 Board Assembly

The ADC121C02XEB evaluation board comes

fully assembled and ready for use. The provided

jumpers are in their recommended locations and

suit the needs of most users. Refer to the Bill of

Materials for a description of components, to

Figure 1 for major component placement, and to

Figure 10 for the evaluation board schematic.

While the board has been populated in a manner

that is most advantageous for typical usage, the

board can be customized by adding components

to meet the user’s specific needs. The board

comes ready to use with a DC coupled input

signal (Figure 2). However, by adding DC bias

resistors R1 and R4 (value 4.99kΩ), and changing

C1 to a 1.0uF capacitor, the board can be used

with an AC coupled input signal (Figure 3).

Figure 2: DC Coupled Input Configuration

Figure 3: AC Coupled Input Configuration

If needed, the input can be terminated by adding

an appropriate termination resistor at R3. The

V_IN footprint (J2) has been stuffed with a single-

pin header for testing typical, slow-moving DC

input signals. An SMA footprint is also included

on the PCB and should be used for precise

dynamic performance evaluation. The Bill of

Materials (Section 10) lists an appropriate SMA

connector to use.

The LMP7731 Low-noise, Precision Operational

Amplifier is included on the ADC121C02XEB for

convenient buffering of the analog input. By

default, it is configured as a simple voltage

follower (Figure 4). Resistors R10 and R11 can

be modified to add non-inverting gain to the

circuit. Adding capacitance at C6 configures the

amplifier as a low-pass filter. To incorporate the

input buffer into the signal path, short pins 2 and 3

of JP1.

Figure 4: Input Buffer Configuration

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The LM4050-4.1 Precision, Micropower, Shunt

Voltage Reference is included on the

ADC121C02XEB as a clean reference solution for

the ADC. To evaluate the ADC using the

LM4050, simply short pins 1 & 2 of JP7, and move

the VA_SELECT jumper to pins 7 & 8 of JP5

(Figure 5).

Figure 5: LM4050 Jumper Configuration

3.0 Quick Start

The ADC121C02XEB evaluation board may be

used in the Stand Alone mode to capture data

with a logic analyzer or third party equipment, or it

may be used in the Computer Mode with a

WaveVision 4 Data Capture Board, referenced

throughout the remainder of this document as

WV4. In both cases, the data may be analyzed

with the WaveVision software.

3.1 Stand Alone Mode

Refer to Figure 1 for locations of test points and

major components.

1. The I

C interface signals (SCL and SDA) may

be driven directly at J1 or with wires soldered

to VIA1 and VIA2 (step 7). A fully-compliant

C interface analyzer should be used to drive

SCL and SDA while monitoring the data

output (SDA).

2. The board provides the option of adding 2kΩ

pull-up resistors to the I

C bus, SCL and SDA.

To enable the pull-up resistors, short pins 1 &

2 of JP2. Assuming the I

C analyzer has

built-in pull-up resistors, the jumper at JP2

must be removed to disable the on-board pull-

up resistors. If the I

C analyzer doesn’t have

built-in pull-up capability, leave JP2 shorted.

3. Connect a clean analog (not switching) +5.0V

power source with a 300mA current limit to

power connector TP7. Ground TP6.

4. Move the shorting jumper at JP5 to pins 9 &

10. NOTE: only two consecutive pins may be

shorted on JP5 at a time.

5. Turn on the power supply.

6. Connect the input signal to the test-point at

J2. The input signal return can be connected

to ground at TP3. Please note the evaluation

board is assembled for a DC-coupled input

source. The board is designed for an AC

coupled input as well. Modifying the board for

an AC coupled input is described above in

Section 2.0. If the source has a 50 ohm output

impedance, install a 51 ohm resistor at R3.

To accurately evaluate the dynamic

performance of the ADC121C021, the source

must be better than 90dB THD.

7. If evaluating the ADC121C027, configure the

C slave address. The address is controlled

by VIA5. With VIA5 left floating, the slave

address of the ADC121C027 will be set to

50hex. Grounding VIA5 sets the address to

51hex. Connecting VIA5 to V

sets the

address to 52hex.

8. If evaluating the ADC121C021, the slave

address is permanently set to 54hex.

9. If evaluating the ADC121C021, the ALERT

pin can be monitored at VIA5.

3.2 Computer Mode

Refer to Figure 1 for locations of test points and

major components. The board comes configured

for “plug-and-play” WaveVision evaluation.

1. Run the WaveVision 4 program, version 4.4 or

higher is required to interface to the WV4

board. While the program is loading, continue

below.

2. Connect a USB cable between the WV4

board and the PC running the WaveVision 4

software.

3. Make the following required jumper

connections, see table 1 for more details:

•JP1 - pins 1 & 2

•JP2 - pins 1 & 2

•JP5 - pins 3 & 4 (All other pins of JP5

must be left open)

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4. Connect the J1 header on the ADC121C021

evaluation board to the WV4 serial connector

(J7) on the WV4 board. Refer to Figure 6 for

the serial connection and Figure 7 for the J1

header pin out.

Figure 6: WV4 to ADC121C02XEB Connection

Figure 7: J1 (WV4S) Header Pin Out

5. Perform step 6 of section 3.1 to drive the

analog input. For information on changing the

configuration of the analog input section, read

Section 2.0 Board Assembly for details. The

board comes ready for a DC coupled input

signal.

6. Connect a clean (not switching) +5.0V power

source with a 350mA current limit to power

connector J1 on the WV4 board. Turn on the

power supply.

7. Refer to Section 5.0 on Software Operation

and Settings to setup the WaveVision 4

software.

4.0 Functional Description

4.1 Jumper Settings

Table 1 describes the function of the various

jumpers on the ADC121C021 evaluation board.

The evaluation board schematic is shown in

Figure 10.

Jumper Pins 1 & 2 Pins 2 & 3

JP1 Select direct V

circuit

Select Amplified V

circuit [LMP7731]

JP2 Enable I

C Pull-up resistors

JP3 Permanently shorted

JP5 VA SELECT (See Below)

JP6 Not Used

JP7 Enable 4.1V Shunt Reference

[LM4050-4.1]

Jumper JP5 (VA SELECT)

Pins 1 & 2

Select 3.3V regulated supply from WV4S

connector.

[LM1117MPX-3.3 on the WV4 board]

Pins 3 & 4 Select 5.0V supply from WV4S connector.

Pins 5 & 6 Not Used

Pins 7 & 8 Select 4.1V shunt reference supply.

[LM4050-4.1]

Pins 9 & 10 Select external supply from TP7.

Table 1: Jumper Configurations

SDA

(

ADC

)

GND

SDA

(

EEPROM

)

+3.3V

SCL

(EEPROM)

GND

+5V

SDA

(

ADC

)

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4.2 Analog Input Signal

There are three basic options for connecting an

input signal to the ADC. The three options

facilitate AC-coupled and DC-coupled input

signals.

The first way to apply an input signal to the ADC

is to connect it to pin 2 of JP1. The signal’s return

(GND) should be connected to TP5. This

configuration provides the input circuit seen in

Figure 8.

Figure 8: Unbiased input circuit.

The second way is to configure the board for an

AC coupled input. DC biasing is available for

inputs applied to J2 but is currently not populated

on the board. By adding DC bias resistors R1 and

R4 (value 4.99kΩ), and changing C1 to a 1.0uF

capacitor, the board can be used with an AC

coupled input signal (Figure 3). To improve the

signal integrity of the connection to the board, an

SMA connector should be stuffed at J2 (V_IN). If

the input source has a 50Ωoutput impedance, a

51Ωresistor can be installed at R3.

The third way to configure the input is by

incorporating the Amplifier into the signal path.

The LMP7731 Low-noise, Precision Operational

Amplifier is included on the board for convenient

buffering of the analog input. By default, it is

configured as a simple voltage follower (Figure 4).

Resistors R10 and R11 can be modified to add

non-inverting gain to the circuit. Adding

capacitance at C6 configures the amplifier as a

low-pass filter. To use the input buffer, simply

move the JP1 jumper to pins 2 & 3.

In any case, it is important that the signal stays

within the allowable input range of the ADC (0V to

). Dynamic input signals should be applied

through a bandpass filter to eliminate the noise

and harmonics commonly associated with signal

sources. To accurately evaluate the performance

of the ADC121C021, the source must be better

than -90dBc THD.

4.3 ADC Reference Circuitry

The ADC121C021 family is internally referenced.

Therefore, the Analog-to-Digital converter gets its

reference from the analog supply (V

). Hence, a

clean analog supply must be used to guarantee

the performance of the ADC.

4.4 I

C Interface

Please refer to section 1.7 of the ADC121C021

datasheet for a detailed description of the I

interface.

The board is designed with I

C pull-up resistors on

both the SDA and SCL lines (R8 & R9). These

resistors are enabled by a single jumper (JP2)

and can easily be added or removed from the I

bus. Also, footprints for series resistors are

designed into the board (R2 & R5). The board is

shipped with 0Ωresistors which can be modified

to provide series resistance if interfacing to a

noisy I

C bus.

The SDA signal is accessible by soldering to VIA1

or connecting to pin 1 of the WV4S connector

(J1). The SCL signal is accessible by soldering to

VIA2 or connecting to pin 5 of J1.

The on-board pull-up resistors can be powered

with an external supply by removing the jumper at

JP2 and connecting the supply to pin 2 of JP2 or

VIA6.

4.5 Alert Function

The ADC121C021 provides a programmable “out-

of-range” Alert function. At the end of every

conversion, the measured voltage is compared to

the values in the V

HIGH

and V

LOW

registers. If the

measured voltage violates either of these values,

an alert condition occurs. The Over Range Alert

flag in the Alert Status Register indicates the V

HIGH

limit has been violated. The Under Range Alert

flag indicated the V

LOW

limit has been violated. If

enabled, the alert condition is also propagated to

bit15 of the Conversion Result Register and the

ALERT output pin.

The Alert function is configured by writing to the

ADC’s internal registers. Refer to Section 1.6 of

the Datasheet for a detailed description of the

ADC’s internal Registers.

Refer to Section 1.8 of the Datasheet for a

detailed description of the Alert function.

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Figure 9: System Settings window

4.6 Automatic Conversion Mode

The Automatic Conversion Mode configures the

ADC to continually perform conversions without

receiving “read” instructions from the I

controller. It is activated by writing a non-zero

value into the Cycle Time bits “D[7:5]” of the

Configuration Register. Various automatic

conversion rates are supported.

Refer to Section 1.9 of the Datasheet for a

detailed description of the Automatic Conversion

Mode.

4.7 Power Supply Connections

The analog supply voltage (V

) can range from

+2.7V to +5.5V. The Evaluation system provides a

handful of power supply options via the JP5

header (see Table 1). V

can be driven by the

LM4050-4.1 Shunt Reference, the LM1117MPX-

3.3 LDO from the WV4 board, or an external

supply. National recommends the LM4050

precision reference for the ADC121C021.

NOTE: In Computer mode, if V

is driven with less

than 3.3V in Computer mode, an external 3.3V

pull-up supply is needed. This will ensure the

3.3V CMOS logic thresholds of the WaveVision4

board are met for SDA and SCL.

To use an external pull-up supply, remove the

jumper at JP2 and connect the supply to pin 2 of

JP2 or VIA6. An external pull-up supply will also

improve the dynamic performance of the ADC.

Typical supply currents when applying an external

supply to TP7 (VA_EXT) and performing ADC

conversions are as follows:

•For V

= +3.3V, I = 8mA

•For V

= +5.0V, I = 11mA

Note: A majority of this current is for powering

devices external to the ADC121C021 such as the

pull-up resistors and the input amplifier.

When operating in the computer mode, the supply

voltage for V

can be applied externally or

supplied directly by the WV4 board through J1.

The external supply voltage is selected by placing

a jumper across pins 9 & 10 of JP5, applying a

power source with a 300mA current limit to TP7,

and grounding TP6. To use the 5.0V supply

directly from the WV4 board, place a shorting

jumper across pins 3 & 4 of JP5. To use the 3.3V

supply directly from the WV4 board, place a

shorting jumper across pins 1 & 2 of JP5. To use

the LM4050 4.1V Shunt Reference, place a

shorting jumper across pins 7 & 8 of JP5. For the

best performance, use a clean external supply.

When operating in Stand Alone mode, always use

an external supply. Apply a +5.0V power source

with a current limit of 100mA to TP7, ground TP6,

and place a shorting jumper across pins 9 & 10 of

JP5.

Note: The +3.3V required to power the EEPROM

(U4) is obtained through J2 from the WV4 board.

The EEPROM is used to identify the type of Eval

Board connected to the WaveVision system in

Computer Mode.

5.0 Software Operation and Settings

The WaveVision 4 software is included with the

WV4 board and the latest version can be

downloaded for free from National's web site at

http://www.national.com/adc. WaveVision4

software version 4.4 or later is required to

evaluate this device with the WaveVision system.

5.1 Software Quick Start

To install this software, follow the procedure in the

WV4 Board User's Guide. Once the software is

installed, run and set it up as follows:

1. Connect the WV4 board to the host computer

with a USB cable.

2. From the WaveVision main menu, go to

Settings and then Capture Settings to open

the System Settings window (Figure 9) and

select the following:

•WaveVision 4 (USB)

•Number of Samples: 2k to 128k, as

desired

•Data Format: Binary

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3. Apply power as specified in Section 4.4, click

on the "Reset" button and await the firmware

to download.

4. Click on the "Close" button to close the

System Settings window.

5. Navigate to the ADC121C021 Eval Board

Window. This is the Control Panel for the

device (Figure 10).

Figure 10: ADC121C021 Control Panel

6. Select the desired I

C Speed from the pull-

down menu (Figure 11).

Figure 11: ADC121C021 Control Panel

7. Set the I

C Slave Address (Figure 10). The

address will default to the correct address for

the ADC121C021 (54hex). If evaluating the

ADC121C027, the I

C address must be

changed to reflect the state of the address

selection pin (ADDR).

8. Press the “Read Registers” button. All of the

9. Configure the ADC’s internal registers. The

Alert function and Automatic Conversion

Mode are setup through the Configuration

value, press the Enter key to write the register

(Figure 10).

10. To capture a dataset from the ADC, navigate

back to the main WaveVision window.

11. After the steps outlined in Section 3.2 are

completed, click on ‘Acquire’ then ‘Samples’

from the Main Menu (you can also press the

F1 shortcut key). If a dialog box opens, select

‘Discard’ or press the Escape (Esc) key to

start collecting new samples.

5.2 Data Analysis

WaveVision main menu will display an output plot.

Make sure there is no clipping of data samples.

Click on the software histogram tab and ensure

data does not exceed the limits of the device. The

samples may be further analyzed by clicking on

the magnifying glass icon, then clicking and

dragging across a specific area of the plot for

better data inspection (Figure 12). See the

WaveVision 4 Board User's Guide for more

details.

Figure 12: Software Histogram: Sine Wave Input

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To view an FFT of the data captured, click on the

‘FFT’ tab. This plot may be zoomed in on the data

plot. A display of dynamic performance

parameters in the form of SINAD, SNR, THD,

SFDR and ENOB will be displayed at the top right

hand corner of the FFT plot (Figure 13).

Figure 13: FFT: 1kHz Sine Wave Input

Acquired data may be saved to a file. Plots may

also be exported as graphics. See the Data

Capture Board User's Guide for details.

5.3 Register Control

The ADC’s internal registers are controlled

through the ADC121C021 Control Panel

(see Figure 7). WaveVision allows both read and

write access to these registers. To read the

registers, simply click the “Read All” button in the

Control Panel window. Each of the registers is

read and displayed in the control panel. To write

to a register, simply type in the 8-bit or 16-bit hex

value to be written to the register and press Enter.

All hex values are assumed to be right justified.

Zeros are written to unspecified bits.

Many functions of the ADC121C021 are enabled

through the internal registers. Please refer to

Section 1.6 on Internal Registers in the Datasheet

for further details.

For example, the following steps will enable the

ALERT pin, set the V

LOW

threshold to ¾ full-scale,

and create an Under Range Alert condition.

-Write 0x04 to the Configuration register.

-Write 0xBFF to the V

LOW

-Ground the analog input (V

-Click the “Read Registers” button to read all the

registers.

-The Alert Status register will read 01hex to

indicate that the V

LOW

value was violated and an

Under Range Alert condition has occurred.

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