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Reference Design
ADS8674, ADS8678
SBAS627 – JULY 2015
ADS867x 14-Bit, 500-kSPS, 4- and 8-Channel, Single-Supply, SAR ADCs with Bipolar Input Ranges
Additional Channels in ADS8678
Multiplexer
Gain (% FS)
1 Features
•1 14-Bit ADCs with Integrated Analog Front-End • 4-, 8-Channel MUX with Auto and Manual Scan • Channel-Independent Programmable Inputs:
– ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V – 10.24 V, 5.12 V, 2.56 V, 1.28 V • 5-V Analog Supply: 1.65-V to 5-V I/O Supply • Constant Resistive Input Impedance: 1 MΩ • Input Overvoltage Protection: Up to ±20 V • On-Chip, 4.096-V Reference with Low Drift • Excellent Performance: – 500-kSPS Aggregate Throughput – DNL: ±0.2 LSB; INL: ±0.25 LSB – Low Drift for Gain Error and Offset – SNR: 85 dB; THD: –100 dB – Low Power: 65 mW • AUX Input → Direct Connection to ADC Inputs • ALARM → High and Low Thresholds per Channel • SPI™-Compatible Interface with Daisy-Chain • Industrial Temperature Range: –40°C to 125°C • TSSOP-38 Package (9.7 mm × 4.4 mm)
1 M:
AIN_0P
OVP
AIN_0GND
OVP
1 M:
1 M:
AIN_1P
OVP
AIN_1GND
OVP
1 M:
1 M:
AIN_2P
OVP
AIN_2GND
OVP
1 M:
1 M:
AIN_3P
OVP
AIN_3GND
OVP
1 M:
1 M:
AIN_4P
OVP
AIN_4GND
OVP
1 M:
1 M:
AIN_5P
OVP
AIN_5GND
OVP
1 M:
1 M:
AIN_6P
OVP
AIN_6GND
OVP
1 M:
1 M:
AIN_7P
OVP
AIN_7GND
OVP
1 M:
AUX_IN AUX_GND
Block Diagram
AVDD
DVDD
PGA
2nd-Order LPF
ADC Driver
VB0
ADS8678 ADS8674
PGA
2nd-Order LPF
ADC Driver
VB1
PGA
2nd-Order LPF
ADC Driver
VB2
PGA
2nd-Order LPF
ADC Driver
VB3
PGA
2nd-Order LPF
ADC Driver
VB4
PGA
2nd-Order LPF
ADC Driver
VB5
PGA
2nd-Order LPF
ADC Driver
VB6
PGA
2nd-Order LPF
ADC Driver
VB7
Digital Logic and Interface
CS SCLK
SDI
14-Bit SAR ADC
SDO DAISY
Oscillator
REFSEL RST/PD
ALARM REFCAP
REFIO
4.096-V Reference
AGND
DGND
REFGND
1
2 Applications
• Power Automation • Protection Relays • PLC Analog Input Modules
3 Description
The ADS8674 and ADS8678 are 4- and 8-channel, integrated data acquisition systems based on a 14-bit successive approximation (SAR) analog-to-digital converter (ADC), operating at a throughput of 500 kSPS. The devices feature integrated analog front-end circuitry for each input channel with overvoltage protection up to ±20 V, a 4- or 8-channel multiplexer with automatic and manual scanning modes, and an on-chip, 4.096-V reference with low temperature drift. Operating on a single 5-V analog supply, each input channel on the devices can support true bipolar input ranges of ±10.24 V, ±5.12 V, ±2.56 V, ±1.28V and ±0.64V, as well as unipolar input ranges of 0 V to 10.24 V, 0 V to 5.12 V, 0 V to 2.56 V and 0 V to 1.28 V. The gain of the analog front-end for all input ranges is accurately trimmed to ensure a high dc precision. The input range selection is software-programmable and independent for each channel. The devices offer a 1-MΩ constant resistive input impedance irrespective of the selected input range.
The ADS8674 and ADS8678 offer a simple SPIcompatible serial interface to the digital host and also support daisy-chaining of multiple devices. The digital supply operates from 1.65 V to 5.25 V, enabling direct interface to a wide range of host controllers.
Device Information(1)
PART NUMBER
PACKAGE
BODY SIZE (NOM)
ADS867x
TSSOP (38)
9.70 mm × 4.40 mm
(1) For all available packages, see the orderable addendum at the end of the datasheet.
Gain Error versus Temperature
0.05
0.03
0.01
-0.01
-0.03
-0.05 ±40
---- ± 2.5*VREF, ---- 1.25*VREF ---- 0.625*VREF, ------0.3125*VREF -------0.156 VREF, ---- + 2.5*VREF ---- + 1.25*VREF, ---- + 0.625*VREF ---- + 0.3125*VREF
±7 26 59 92 Free-Air Temperature (oC)
125
C039
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA.
ADS8674, ADS8678
SBAS627 – JULY 2015
www.ti.com
Table of Contents
1 Features .................................................................. 1 2 Applications ........................................................... 1 3 Description ............................................................. 1 4 Revision History..................................................... 2 5 Device Comparison Table..................................... 3 6 Pin Configuration and Functions ......................... 3 7 Specifications......................................................... 5
7.1 Absolute Maximum Ratings ...................................... 5 7.2 ESD Ratings.............................................................. 5 7.3 Recommended Operating Conditions....................... 5 7.4 Thermal Information .................................................. 5 7.5 Electrical Characteristics.......................