ad7938bsu-reel7 Analog Devices, Inc., ad7938bsu-reel7 Datasheet

ad7938bsu-reel7

Manufacturer Part Number

ad7938bsu-reel7

Description

8-channel, 1.5 Msps, 12-bit And 10-bit Parallel Adcs With A Sequencer

Manufacturer

Analog Devices, Inc.

Datasheet

1.AD7938BSU-REEL7.pdf (36 pages)

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FEATURES

Throughput rate: 1.5 MSPS

Specified for V

Power consumption

8 analog input channels with a sequencer

Software-configurable analog inputs

Accurate on-chip 2.5 V reference

70 dB SINAD at 50 kHz input frequency

No pipeline delays

High speed parallel interface—word/byte modes

Full shutdown mode: 2 μA maximum

32-lead LFCSP and TQFP packages

GENERAL DESCRIPTION

The AD7938/AD7939 are 12-bit and 10-bit, high speed, low

power, successive approximation (SAR) analog-to-digital

converters (ADCs). The parts operate from a single 2.7 V to

5.25 V power supply and feature throughput rates up to

1.5 MSPS. The parts contain a low noise, wide bandwidth,

differential track-and-hold amplifier that can handle input

frequencies up to 50 MHz.

The AD7938/AD7939 feature eight analog input channels with

a channel sequencer that allows a preprogrammed selection of

channels to be converted sequentially. These parts can operate

with either single-ended, fully differential, or pseudo

differential analog inputs.

The conversion process and data acquisition are controlled

using standard control inputs that allow easy interfacing with

microprocessors and DSPs. The input signal is sampled on the

falling edge of CONVST and the conversion is also initiated at

this point.

The AD7938/AD7939 have an accurate on-chip 2.5 V reference

that can be used as the reference source for the analog-to-digital

conversion. Alternatively, this pin can be overdriven to provide

an external reference.

Rev. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

6 mW maximum at 1.5 MSPS with 3 V supplies

13.5 mW maximum at 1.5 MSPS with 5 V supplies

8-channel single-ended inputs

4-channel fully differential inputs

4-channel pseudo differential inputs

7-channel pseudo differential inputs

±0.2% maximum @ 25°C, 25 ppm/°C maximum

of 2.7 V to 5.25 V

8-Channel, 1.5 MSPS, 12-Bit and 10-Bit

Parallel ADCs with a Sequencer

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700

Fax: 781.461.3113

These parts use advanced design techniques to achieve very

low power dissipation at high throughput rates. They also

feature flexible power management options. An on-chip control

including analog input range and configuration, output coding,

power management, and channel sequencing.

PRODUCT HIGHLIGHTS

Table 1. Related Devices

Device

AD7933/AD7934

AD7938-6

AD7934-6

REFOUT

REFIN/

High throughput with low power consumption.

Eight analog inputs with a channel sequencer.

Accurate on-chip 2.5 V reference.

Single-ended, pseudo differential, or fully differential

analog inputs that are software selectable.

Single-supply operation with V

function allows the parallel interface to connect directly to

3 V or 5 V processor systems independent of V

No pipeline delay.

Accurate control of the sampling instant via a CONVST

input and once-off conversion control.

PARALLEL INTERFACE/CONTROL REGISTER

SEQUENCER

FUNCTIONAL BLOCK DIAGRAM

DB0 DB11

MUX

I/P

No. of Bits

12/10

VREF

T/H

2.5V

AGND

Figure 1.

AD7938/AD7939

RD WR W/B

No. of Channels

DRIVE

CONTROL

12-/10-BIT

SAR ADC

AD7938/AD7939

AND

function. The V

www.analog.com

DGND

Speed

1.5 MSPS

625 kSPS

CLKIN

CONVST

BUSY

DRIVE

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ad7938bsu-reel7 Summary of contents

Page 1

... Accurate control of the sampling instant via a CONVST 7. input and once-off conversion control. Table 1. Related Devices Device AD7933/AD7934 AD7938-6 AD7934-6 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 Fax: 781.461.3113 ©2004–2007 Analog Devices, Inc. All rights reserved. AD7938/AD7939 AGND DD AD7938/AD7939 2.5V VREF CLKIN 12-/10-BIT SAR ADC CONVST ...

Page 2

AD7938/AD7939 TABLE OF CONTENTS Features .............................................................................................. 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Product Highlights ........................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 AD7938 Specifications................................................................. 3 AD7939 Specifications................................................................. 5 Timing Specifications .................................................................. 7 Absolute Maximum Ratings............................................................ 8 ...

Page 3

SPECIFICATIONS AD7938 SPECIFICATIONS 2 5.25 V, internal/external V DD DRIVE unless otherwise noted. A MIN MAX Table 2. Parameter DYNAMIC PERFORMANCE 2 Signal-to-Noise and Distortion (SINAD) 2 Signal-to-Noise ...

Page 4

AD7938/AD7939 Parameter REFERENCE INPUT/OUTPUT 5 V Input Voltage REF DC Leakage Current V Output Voltage REFOUT V Temperature Coefficient REFOUT V Noise REF V Output Impedance REF V Input Capacitance REF LOGIC INPUTS Input High Voltage, V INH Input Low ...

Page 5

AD7939 SPECIFICATIONS 2 5.25 V, internal/external V DD DRIVE unless otherwise noted. A MIN MAX Table 3. Parameter DYNAMIC PERFORMANCE Signal-to-Noise and Distortion (SINAD) 2 Total Harmonic Distortion ...

Page 6

AD7938/AD7939 Parameter REFERENCE INPUT/OUTPUT 5 V Input Voltage REF 4 DC Leakage Current V Output Voltage REFOUT V Temperature Coefficient REFOUT V Noise REF V Output Impedance REF V Input Capacitance REF LOGIC INPUTS Input High Voltage, V INH Input ...

Page 7

TIMING SPECIFICATIONS 2 5.25 V, internal/external V DD DRIVE T , unless otherwise noted. MAX Table 4. Limit MIN MAX 1 Parameter AD7938 AD7939 Unit 2 f 700 700 kHz ...

Page 8

AD7938/AD7939 ABSOLUTE MAXIMUM RATINGS T = 25°C, unless otherwise noted. A Table 5. Parameter V to AGND/DGND AGND/DGND DRIVE Analog Input Voltage to AGND Digital Input Voltage to DGND DRIVE DD Digital Output Voltage ...

Page 9

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS DB0 PIN 1 DB1 INDICATOR DB2 DB3 4 AD7938/AD7939 21 AGND DB4 TOP VIEW DB5 (Not to Scale) DB6 7 ...

Page 10

AD7938/AD7939 Pin No. Mnemonic Description 21 AGND Analog Ground. This is the ground reference point for all analog circuitry on the AD7938/AD7939. All analog input signals and any external reference signal should be referred to this AGND voltage. The AGND ...

Page 11

TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted. A –60 100mV p-p SINE WAVE ON V AND/ DECOUPLING DIFFERENTIAL/SINGLE-ENDED MODE –70 INT REF –80 –90 EXT REF –100 –110 –120 10 210 410 610 SUPPLY RIPPLE ...

Page 12

AD7938/AD7939 4 SINGLE-ENDED MODE POSITIVE DNL 0 NEGATIVE DNL –1 0.25 0.50 0.75 1.00 1.25 1.50 1.75 V (V) REF Figure 10. AD7938 DNL vs. V REF DIFFERENTIAL MODE 10 V SINGLE-ENDED MODE ...

Page 13

TERMINOLOGY Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, 1 LSB below the first code transition, and full scale, ...

Page 14

AD7938/AD7939 Track-and-Hold Acquisition Time The track-and-hold amplifier returns to track mode at the end of conversion. The track-and-hold acquisition time is the time required for the output of the track-and-hold amplifier to reach its final value, within ±½ LSB, after ...

Page 15

ON-CHIP REGISTERS The AD7938/AD7939 have two on-chip registers that are necessary for the operation of the device. These are the control register, which is used to set up different operating conditions, and the shadow register, which is used to program ...

Page 16

AD7938/AD7939 SEQUENCER OPERATION The configuration of the SEQ and SHDW bits in the control register allows the user to select a particular mode of operation of the sequencer function. Table 11 outlines the four modes of operation of the sequencer. ...

Page 17

SHADOW REGISTER The shadow register on the AD7938/AD7939 is an 8-bit, write- only register. Data is loaded from DB0 to DB7 on the rising edge The eight LSBs load into the shadow register. The information is written ...

Page 18

AD7938/AD7939 CIRCUIT INFORMATION The AD7938/AD7939 are fast, 8-channel, 12-bit and 10-bit, single-supply, successive approximation analog-to-digital converters. The parts can operate from a 2 5.25 V power supply and feature throughput rates up to 1.5 MSPS. The AD7938/AD7939 provide ...

Page 19

LSB = 2 × V /4096 (AD7938) REF 1 LSB = 2 × V /1024 (AD7939) REF 011...111 011...110 000...001 000...000 111...111 100...010 100...001 100...000 – LSB V REF REF Figure 18. AD7938/AD7939 Ideal Transfer Characteristic with ...

Page 20

AD7938/AD7939 – 50kHz IN –45 –50 –55 –60 –65 –70 –75 –80 –85 –90 10 100 R (Ω) SOURCE Figure 21. THD vs. Source Impedance in Single-Ended Mode – 50kHz IN –65 –70 –75 –80 –85 ...

Page 21

V REF p-p V REF p-p COMMON-MODE VOLTAGE *ADDITIONAL PINS OMITTED FOR CLARITY. Figure 25. Differential Input Definition The amplitude of the differential signal is the difference between the signals applied to the V and V IN+ differential pair (that ...

Page 22

AD7938/AD7939 220Ω 2 × V p-p REF V+ 440Ω GND 27Ω V– 220Ω 220Ω 220Ω V+ 27Ω A V– + 10kΩ 20kΩ Figure 28. Dual Op Amp Circuit to Convert a Single-Ended Bipolar Signal into a Differential Unipolar Signal 220Ω ...

Page 23

Using the Sequencer: Programmable Sequence (SEQ = 0, SHDW = 1) The AD7938/AD7939 can be configured to automatically cycle through a number of selected channels using the on-chip programmable sequencer by setting SEQ = 0 and SHDW = 1 in ...

Page 24

AD7938/AD7939 Alternatively, an external reference can be applied to the V V pin of the AD7938/AD7939. An external reference REFOUT input is selected by setting the REF bit in the internal control register to 0. The external reference input range ...

Page 25

PARALLEL INTERFACE The AD7938/AD7939 have a flexible, high speed, parallel interface. This interface is 12-bits (AD7938) or 10-bits (AD7939) wide and is capable of operating in either word (W/ B tied high) or byte (W/ B tied low) mode. The ...

Page 26

AD7938/AD7939 Reading Data from the AD7938/AD7939 With the W/ B pin tied logic high, the AD7938/AD7939 interface operates in word mode. In this case, a single read operation from the device accesses the conversion data-word on Pins DB0/DB2 to Pin ...

Page 27

Writing Data to the AD7938/AD7939 With W/ B tied logic high, a single write operation transfers the full data-word on DB0 to DB11 to the control register on the AD7938/AD7939. The DB8/HBEN pin assumes its DB8 function. Data written to ...

Page 28

AD7938/AD7939 POWER MODES OF OPERATION The AD7938/AD7939 have four different power modes of operation. These modes are designed to provide flexible power management options. Different options can be chosen to optimize the power dissipation/throughput rate ratio for differing applications. The ...

Page 29

POWER vs. THROUGHPUT RATE A considerable advantage of powering the ADC down after a conversion is that the power consumption of the part is significantly reduced at lower throughput rates. When using the different power modes, the AD7938/AD7939 are only ...

Page 30

AD7938/AD7939 AD7938/AD7939 to ADSP-21065L Interface Figure 44 shows a typical interface between the AD7938/AD7939 and the ADSP-21065L This interface is an example of one of three DMA handshake modes. The MS control line is actually three memory select X lines. ...

Page 31

APPLICATION HINTS GROUNDING AND LAYOUT The printed circuit board that houses the AD7938/AD7939 should be designed so that the analog and digital sections are separated and confined to certain areas of the board. This facilitates the use of ground planes ...

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