Image AD7705
型号: AD7705
厂商: Analog Devices Inc Analog Devices Inc
分类: 半导体
描述: 3 V/5 V, 1 mW 2-/3-channel 16-bit, sigma-delta adcs
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3 V/5 V, 1 mW  
a
2-/3-Channel 16-Bit, Sigma-Delta ADCs  
AD7705/AD7706*  
FUNCTIONAL BLOCK DIAGRAM  
FEATURES  
AD7705: Two Fully Differential Input Channel ADCs  
AD7706: Three Pseudo Differential Input Channel ADCs  
16 Bits No Missing Codes  
V
DD  
REF IN(–)  
REF IN(+)  
AD7705/AD7706  
0.003% Nonlinearity  
Programmable Gain Front End  
Gains from 1 to 128  
Three-Wire Serial Interface  
SPI™, QSPI™, MICROWIRE™ and DSP Compatible  
Schmitt Trigger Input on SCLK  
Ability to Buffer the Analog Input  
2.7 V to 3.3 V or 4.75 V to 5.25 V Operation  
Power Dissipation 1 mW max @ 3␣ V  
Standby Current 8 A max  
CHARGE  
BALANCING  
A/D CONVERTER  
ANALOG  
INPUT  
CHANNELS  
- ⌬  
MODULATOR  
PGA  
MAX  
BUFFER  
A = 1Ϸ128  
DIGITAL FILTER  
16-Lead DIP, 16-Lead SOIC and TSSOP Packages  
SERIAL INTERFACE  
REGISTER BANK  
GENERAL DESCRIPTION  
SCLK  
CS  
MCLK IN  
The AD7705/AD7706 are complete analog front ends for low  
frequency measurement applications. These two-/three-channel  
devices can accept low level input signals directly from a trans-  
ducer and produce a serial digital output. They employ a sigma-  
delta conversion technique to realize up to 16 bits of no missing  
codes performance. The selected input signal is applied to a  
proprietary programmable gain front end based around an ana-  
log modulator. The modulator output is processed by an on-  
chip digital filter. The first notch of this digital filter can be  
programmed via an on-chip control register allowing adjustment  
of the filter cutoff and output update rate.  
CLOCK  
GENERATION  
MCLK OUT  
DIN  
DOUT  
GND  
DRDY RESET  
using the input serial port. The part contains self-calibration and  
system calibration options to eliminate gain and offset errors on  
the part itself or in the system.  
CMOS construction ensures very low power dissipation, and the  
power-down mode reduces the standby power consumption to  
20␣ µW typ. These parts are available in a 16-lead, 0.3 inch-wide,  
plastic dual-in-line package (DIP), a 16-lead wide body (0.3  
inch) small outline (SOIC) package and also a low profile 16-  
lead TSSOP.  
The AD7705/AD7706 operate from a single 2.7 V to 3.3 V or  
4.75 V to 5.25 V supply. The AD7705 features two fully differ-  
ential analog input channels while the AD7706 features three  
pseudo differential input channels. Both devices feature a differ-  
ential reference input. Input signal ranges of 0 mV to +20␣ mV  
through 0 V to +2.5V can be incorporated on both devices when  
operating with a VDD of 5 V and a reference of 2.5 V. They can  
also handle bipolar input signal ranges of ±20mV through ±2.5V,  
which are referenced to the AIN(–) inputs on the AD7705 and to  
the COMMON input on the AD7706. The AD7705/AD7706,  
with 3 V supply and a 1.225 V reference, can handle unipolar  
input signal ranges of 0 mV to +10mV through 0 V to +1.225V.  
Its bipolar input signal ranges are ±10␣ mV through ±1.225␣ V.  
The AD7705/AD7706 thus perform all signal conditioning and  
conversion for a two- or three-channel system.  
PRODUCT HIGHLIGHTS  
1. The AD7705/AD7706 consumes less than 1 mW at 3 V  
supplies and 1␣ MHz master clock, making it ideal for use in  
low power systems. Standby current is less than 8␣ µA.  
2. The programmable gain input allows the AD7705/AD7706  
to accept input signals directly from a strain gage or trans-  
ducer, removing a considerable amount of signal conditioning.  
3. The AD7705/AD7706 is ideal for microcontroller or DSP  
processor applications with a three-wire serial interface re-  
ducing the number of interconnect lines and reducing the  
number of opto-couplers required in isolated systems.  
4. The part features excellent static performance specifications  
with 16 bits, no missing codes, ±0.003% accuracy and low  
rms noise (<600␣ nV). Endpoint errors and the effects of  
temperature drift are eliminated by on-chip calibration op-  
tions, which remove zero-scale and full-scale errors.  
The AD7705/AD7706 are ideal for use in smart, microcontroller  
or DSP-based systems. They feature a serial interface that can  
be configured for three-wire operation. Gain settings, signal  
polarity and update rate selection can be configured in software  
*Protected by U.S. Patent Number 5,134,401.  
SPI and QSPI are trademarks of Motorola, Inc.  
MICROWIRE is a trademark of National Semiconductor.  
REV. A  
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  
which may result from its use. No license is granted by implication or  
otherwise under any patent or patent rights of Analog Devices.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781/329-4700  
Fax: 781/326-8703  
World Wide Web Site: http://www.analog.com  
© Analog Devices, Inc., 1998