ADS8866_14 Datasheet, PDF (26/42 Pages) Texas Instruments – 16-Bit, 100-kSPS, Serial Interface, microPower, Miniature Single-Ended Input, SAR Analog-to-Digital Converter

ADS8866
SBAS614A – MAY 2013 – REVISED DECEMBER 2013
www.ti.com
Reference Driver Circuit for V_REF = 3 V in Ultralow Power, Lower Throughput Applications
The application circuit in Figure 55 shows the schematic of a complete reference driver circuit that generates a
voltage of 3 V dc using a single 3.3-V supply. This ultralow power reference block is suitable to drive the
ADS8866 for power-sensitive applications at a relatively lower throughput. This design uses the high-precision
REF3330 circuit that provides an accurate 3-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 
AVDD
REF3330
IN OUT
GND
10 k 
1 µF
-
2.2 k 
++
OPA333
AVDD
AVDD
REF AVDD
AINP
V+
CONVST
ADS8866
AINM
GND
Figure 55. Reference Driver Circuit Schematic with V_REF = 3 V
The reference buffer is designed with the low-power OPA333 that can operate from a 3.3-V supply at an
extremely low quiescent current of 28 µA. The AOL of amplifier interacting with a 47-µF capacitor, a 10-Ω ESR
(of a capacitor), and a 2.2-kΩ additional open-look output impedance limit the wideband noise contribution from
the amplifier to 3 kHz bandwidth. These three components are critical for good stability and maintaining the
amplifier with more than a 50° phase margin. In addition, the two 0.1-µF capacitors decouple the high-frequency
currents produced by the ADC reference input during conversions.
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