ADS8863_14 Datasheet, PDF (31/49 Pages) Texas Instruments – 16-Bit, 680-kSPS, Serial Interface, microPower, Miniature, True-Differential Input, SAR Analog-to-Digital Converter

ADS8863
www.ti.com
SBAS571A – MAY 2013 – REVISED DECEMBER 2013
Reference Driver Circuit for V_REF = 2.5 V in Ultralow Power, Lower Throughput Applications
The application circuit in Figure 68 shows the schematic of a complete reference driver circuit that generates a
voltage of 2.5 V dc using a single 3.3-V supply. This ultralow power reference block is suitable to drive the
ADS8863 for power-sensitive applications at a relatively lower throughput. This design uses the high-precision
REF3325 circuit that provides an accurate 2.5-V reference voltage at an extremely low quiescent current of 5 µA.
The output broadband noise of the reference is heavily filtered by a low-pass filter with a 3-dB cutoff frequency of
16 Hz.
1 k 
1 µF
AVDD
REF3325
IN OUT
GND
10 k 
1 µF
-
++
OPA333
AVDD
4.7 
22 µF
AVDD
REF AVDD
AINP
V+
CONVST
ADS8863
AINM
GND
Figure 68. Schematic of Reference Driver Circuit with V_REF = 2.5 V DC
The reference buffer is designed using the low-power OPA333 that can operate from a 3.3-V supply at an
extremely low quiescent current of 28 µA. The wideband noise contribution from the amplifier is limited by a low-
pass filter of a cutoff frequency equal to 1.5 kHz, formed by a 4.7-Ω resistor in combination with a 22-µF
capacitor. The 4.7-Ω series resistor creates an additional drop in the reference voltage, which is corrected by a
dual-feedback configuration.
For step-by-step design procedure, circuit schematics, bill of materials, PCB files, simulation results, and test
results, using a similar device, refer to 18-Bit, 10kSPS Data Acquisition (DAQ) Block Optimized for Ultra Low
Power < 1mW (SLAU514).
Copyright © 2013, Texas Instruments Incorporated
Product Folder Links: ADS8863
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