3 V/5 V, 450 μA
16-Bit, Sigma-Delta ADC
AD7715
FEATURES
Charge-balancing ADC
16-bits no missing codes
0.0015% nonlinearity
Programmable gain front end
Gains of 1, 2, 32 and 128
Differential input capability
Three-wire serial interface
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
FUNCTIONAL BLOCK DIAGRAM
REF IN(–)
REF IN(+)
AV
DD
DV
DD
CHARGE BALANCING
ADC
AIN(+)
AIN(–)
BUFFER
PGA
A = 1 TO 128
SERIAL
INTERFACE
REGISTER BANK
Σ-∆
MODULATOR
DIGITAL
FILTER
CLOCK
GENERATION
MCLK IN
MCLK OUT
RESET
SCLK
CS
DIN
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.
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.
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.
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.
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 part features excellent static performance specifications
with 16-bits no missing codes, ±0.0015% 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.
2.
3.
4.
Rev. D
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rights of third parties that may result from its use. Specifications subject to change without notice. No
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©2009 Analog Devices, Inc. All rights reserved.
08519-001
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