AD7715 Datasheet, PDF (1/31 Pages) Analog Devices – 3 V/5 V, 450 uA 16-Bit, Sigma-Delta ADC

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3 V/5 V, 450 ␮A
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␣ ␮A max @ 3␣ V Supplies
Low-Pass Filter with Programmable Output Update
16-Lead SOIC/DIP/TSSOP
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 sigma-delta 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 pro-
cessed by an on-chip digital filter. The first notch of this digital
filter can be programmed via the on-chip control register allow-
ing adjustment of the filter cutoff and output update rate.
The AD7715 features a differential analog input as well as a dif-
ferential 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 config-
ured 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.
FUNCTIONAL BLOCK DIAGRAM
REF IN(–) REF IN(+)
AV_DD
DV_DD
AIN(+)
AIN(–)
BUFFER PGA
CHARGE BALANCING
A/D CONVERTER
SIGMA-DELTA
MODULATOR
DIGITAL
FILTER
A = 1–128
SERIAL
INTERFACE
CLOCK
GENERATION
REGISTER BANK
AD7715
AGND DGND
MCLK IN
MCLK OUT
RESET
SCLK
CS
DIN
DOUT
DRDY
CMOS construction ensures very low power dissipation, and the
power-down mode reduces the standby power consumption to
50␣ µW typ. The part is available in a 16-lead, 0.3 inch-wide,
plastic dual-in-line package (DIP) as well as a 16-lead 0.3 inch-
wide small outline (SOIC) 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 remov-
ing 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
opto-couplers required in isolated systems. The part con-
tains on-chip registers which allow software control over
output update rate, input gain, signal polarity and calibration
modes.
4. 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 op-
tions, which remove zero-scale and full-scale errors.
SPI and QSPI are trademarks of Motorola, Inc.
MICROWIRE is a trademark of National Semiconductor Corporation.
*Protected by U.S. Patent No: 5,134,401.
See page 30 for data sheet index.
REV. C
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