Analog Inputs; Analog Input Support Circuitry On The Ads126Xevm - Texas Instruments ADS126 EVM-PDK Series User Manual

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Analog Inputs

The ADS126x has a total of 11 analog input pin: AIN0 through AIN9 plus a common reference input,
AINCOM. This design allows the ADS126x to be configured for up to five differential input pairs, ten
single-ended inputs referenced to a common voltage, or a combination of single-ended and differential
inputs. The flexible input multiplexer of the ADS126x allows any two inputs to be selected for either the
positive or negative ADC input.
When measuring single-ended input signals, any input pin may be used as a common voltage reference.
However, AINCOM is specially designated to serve this purpose because it provides a bias voltage (level-
shift function) for floating sensors to meet the common-mode voltage requirements of the ADS126x inputs.
All of the analog inputs to the ADC are pinned out on the ADS126xEVM. The supporting circuitry provides
filtering and ratiometric connections for a variety of sensors. Additionally, a separate terminal block (J4) is
provided for thermocouple inputs.
circuitry.
DAUGHTER-ANALOG
Bottom Side
(Connects to MMB0)
MMB0 passes signals through to J10
Figure 10. Analog Input Support Circuitry on the ADS126xEVM
SBAU206 – April 2015
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Figure 10 shows the schematic of the ADS126xEVM analog input
J2
1 IN0
2 IN1
3 IN2
4 IN3
5 IN4
6 IN5
7 IN6
8 IN7
9 AINCOM
10
ED555/10DS
GND
TERMINAL BLOCK Ratiometric
1
Top Side Connection
2
Jumper
JP1
J3
1 IN0
R17 sets up a 1.95V reference
2 IN1 voltage with 500uA IDAC
3 IN2
4 IN3
5 IN4
6 IN5
7 IN6
8 IN7
AINCOM1
9
10 AINCOM
11 C22
47pF
12
13
GND
14
15
16
17
18
REFOUT1
19
20 REFOUT
GND
R22
Thermistor (for CJC) NI
R23
2.2k @ 25°C
12k
R24
NI
Configured for 250uA IDAC
in single supply configuration R25
(Install 0-Ohms in R22 & R24) 1.2k
J4 GND
2
Thermocouple
Input 1
ED555/2DS R31
TERMINAL BLOCK NI
Top Side
Cold Junction = GND
GND
Sensor Bias
Jumper
JP5
Copyright © 2015, Texas Instruments Incorporated
IN1
IN0 R1 47
C1 X2Y Capacitor
47pF
R2
C3
NI
GND GND
100nF
C4
47pF
IN1 R6 47
IN2
IN2 R8 47
X2Y Capacitor
C7
47pF
R10
C9
NI GND GND
100nF
C11
47pF
IN3 R12 47
IN6
IN4
IN4 R16 47
C16 X2Y Capacitor
47pF
R17 C18
GND GND
3.9k
100nF
C21
47pF
IN5 R18 47
2
AVSS Connection
1
Jumper
JP3
R19
620 R19 increases REF3N voltage to >0.3V when used with
500uA IDAC in single supply and ratiometric configurations
AVSS
IN6 R20 47
C23 X2Y Capacitor
47pF
C25
GND GND
100nF
C26
47pF
IN7 R21 47
INPUT FILTERING
CM f-3dB = 72 MHz
DM f-3dB = 16.9 kHz
IN6
IN7
R26 499
C34
1nF
C36
GND GND
100nF
C37
1nF
R28 499
FILTERING
CM f-3dB = 319 kHz
DM f-3dB = 1.59 kHz
1
2 AINCOM
ADS126xEVM Hardware
AIN0
(EXT REF1 P)
C2 NI
GND
AIN1
(EXT REF1 N)
AIN2
(EXT REF2 P)
C8 NI
GND
AIN3
(EXT REF2 N)
AIN4
(EXT REF3 P)
C17 NI
GND
AIN5
(EXT REF3 N)
AIN6
(Test SIG P)
C24 NI
GND
AIN7
(Test SIG N)
X2Y Capacitor
AIN8
C35 NI
GND
AIN9
ADS126xEVM-PDK
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