Voltage Reference, Aux Input, And Supply Decoupling; Figure 3-2. Voltage Reference, Aux Input, And Supply - Texas Instruments ADS8688EVM-PDK User Manual

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3.2 Voltage Reference, Aux Input, and Supply Decoupling

The circuit shown in Figure 3-2
on the ADS8688 to use an external voltage reference, but typically the integrated internal reference is sufficient.
In cases where you need to use an enthral voltage reference it can be connected via the REF test point. The
capacitors for decoupling match the recomendations in the ADS8688 data sheet. The layout (see
uses the shortest possible connections to the decouplign capacitors and connections the ground end to the GND
plane using vias. The AUX input is a standard SAR input and does not have an analog front end. Thus, this input
cannot accept high voltage input signals (Vin Full Scale = VREF = 4.096V). Furthermore, this input requires an
external buffer amplifier U4 to achieve good settling.
J09
GND
Figure 3-2. Voltage Reference, Aux Input, and Supply Decoupling
SBAU230C – AUGUST 2014 – REVISED MARCH 2021
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illustrates the decoupling on AVDD, DVDD, and the reference IO. It is possible
AVDD
C4
DVDD
1µF
C5 C6
25V
25V 1µF
10uF 25V
U1
GND
9
AVDD
30
AVDD
34
DVDD
A0+
16
AIN_0P
A0-
17
AIN_0GND
A1+
18
AIN_1P
A1- 19
AIN_1GND
A2+ 21
AIN_2P
A2- 20
AIN_2GND
A3+
23
AIN_3P
A3-
22
AIN_3GND
A4+
25
AIN_4P
A4-
24
AIN_4GND
A5+
27
AIN_5P
A5-
26
AIN_5GND
A6+ 12
AIN_6P
A6- 13
AIN_6GND
A7+ 14
AIN_7P
A7-
15
AIN_7GND
R26
10
AUX_IN
11
49.9
AUX_GND
C12
50V
ADS8688IDBT
R27
1000pF
49.9
GND
AVDD
C13
100nF
50V
GND
4
1
1 3
U4
OPA320AIDBVR
R30
1.00k
GND
GND
Copyright © 2021 Texas Instruments Incorporated
GND
GND
38
CS
37
SCLK
R9
1
SDI
49.9
36
SDO
R16
RST
2
RST/PD
47.0k
R17
3
DAISY
47.0k
35 Alt
DNC
RefSel
4
REFSEL
7
REFCAP
5
REFIO
6
REFGND
8
AGND
28
AGND
29
AGND
31
AGND
REF
32
AGND
33
DGND
GND
AUX
EVM Analog Interface
Figure
R6
CS
49.9
R7
SCLK_R
49.9
R8
SCLK
49.9
SDI
R10
SDO
49.9
DVDD
R36
GND
DNP DVDD
47.0k
R19
GND
47.0k
C7 C8 C9
25V 1µF 25V
R29
100 10uF 25V 22uF
GND
ADS8688EVM-PDK Evaluation Module
8-1)
5