3 V/5 V, 450 μA
16-Bit, Sigma-Delta ADC
AD7715
FUNCTIONAL BLOCK DIAGRAM
FEATURES
AV
DV
DD
REF IN(–) REF IN(+)
DD
Charge-balancing ADC
16-bits no missing codes
0.0015% nonlinearity
Programmable gain front end
Gains of 1, 2, 32 and 128
CHARGE BALANCING
ADC
Σ-∆
DIGITAL
AIN(+)
AIN(–)
MODULATOR
FILTER
BUFFER
PGA
Differential input capability
Three-wire serial interface
A = 1 TO 128
CLOCK
GENERATION
MCLK IN
MCLK OUT
RESET
SERIAL
SPI-, QSPI™-, MICROWIRE™-, and DSP-compatible
Ability to buffer the analog input
3 V (AD7715-3) or 5 V (AD7715-5) operation
Low supply current: 450 μA maximum @ 3 V supplies
Low-pass filter with programmable output update
16-lead SOIC/PDIP/TSSOP
INTERFACE
SCLK
CS
DIN
REGISTER BANK
DOUT
DRDY
AD7715
AGND
DGND
Figure 1.
GENERAL DESCRIPTION
The AD7715 is a complete analog front end for low frequency
measurement applications. The part can accept low level input
signals directly from a transducer and outputs a serial digital
word. It employs a Σ-Δ conversion technique to realize up to
16 bits of no missing codes performance. The input signal is
applied to a proprietary programmable gain front end based
around an analog modulator. The modulator output is processed
by an on-chip digital filter. The first notch of this digital filter
can be programmed via the on-chip control register allowing
adjustment of the filter cutoff and output update rate.
CMOS construction ensures very low power dissipation, and
power-down mode reduces the standby power consumption to
50 μW typical. The part is available in a 16-lead, 0.3 inch-wide,
plastic dual-in-line package (PDIP) as well as a 16-lead 0.3 inch
wide small outline (SOIC_W) package and a 16-lead TSSOP
package.
PRODUCT HIGHLIGHTS
1. The AD7715 consumes less than 450 μA in total supply
current at 3 V supplies and 1 MHz master clock, making it
ideal for use in low-power systems. Standby current is less
than 10 μA.
2. The programmable gain input allows the AD7715 to accept
input signals directly from a strain gage or transducer
removing a considerable amount of signal conditioning.
3. The AD7715 is ideal for microcontroller or DSP processor
applications with a three-wire serial interface reducing the
number of interconnect lines and reducing the number
of optocouplers required in isolated systems. The part
contains on-chip registers which allow software control
over output update rate, input gain, signal polarity, and
calibration modes.
The AD7715 features a differential analog input as well as a
differential reference input. It operates from a single supply (3 V
or 5 V). It can handle unipolar input signal ranges of 0 mV to
20 mV, 0 mV to 80 mV, 0 V to 1.25 V and 0 V to 2.5 V. It can
also handle bipolar input signal ranges of 20 mV, 80 mV,
1.25 V and 2.5 V. These bipolar ranges are referenced to the
negative input of the differential analog input. The AD7715
thus performs all signal conditioning and conversion for a
single channel system.
The AD7715 is ideal for use in smart, microcontroller, or DSP-
based systems. It features a serial interface that can be configured
for three-wire operation. Gain settings, signal polarity, and
update rate selection can be configured in software 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.
4. The part features excellent static performance specifications
with 16-bits no missing codes, 0.0015ꢀ accuracy, and low
rms noise (<550 nV). Endpoint errors and the effects of
temperature drift are eliminated by on-chip calibration
options, which remove zero-scale and full-scale errors.
Rev. D
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 registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2009 Analog Devices, Inc. All rights reserved.
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