Texas Instruments ADS1261EVM User manual

1
SBAU293–March 2018
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
User's Guide
SBAU293–March 2018
ADS1261 and ADS1235 Evaluation Module
ADS1261, ADS1235 Evaluation Module (ADS1261EVM Shown)
The ADS1261EVM and ADS1235EVM are evaluation module kits providing hardware and software
support for evaluation of the ADS1261, or ADS1235, delta-sigma analog-to-digital converter (ADC). The
kit utilizes the TM4C1294NCPDT processor to communicate with the ADC via SPI and provide
communication with a PC over USB interface. The kit also includes a software application that runs on a
PC allowing for register manipulation and data collection from the ADC. The ADS1261 and ADS1235 EVM
kit include the ADS12xx device along with a USB micro cable and downloadable supporting software
(SW).
This document includes a detailed description of the hardware (HW), software, bill of materials, and
schematic for the EVM.
Throughout this document, the term EVM is synonymous with ADS1261EVM and ADS1235EVM,
demonstration kit, and evaluation module. The term EVM applies to both the ADS1261EVM and
ADS1235EVM. The term GUI is synonymous with Delta-Sigma ADC EvaluaTIon Software, core
application, and EVM software. The use of Tiva™ is synonymous with the TM4C1294NCPDT
microcontroller.
Table 1. Related Documentation
Device Literature Number
ADS1261 SBAS760
ADS1235 SBAS824

www.ti.com
2SBAU293–March 2018
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
Contents
1 EVM Overview ............................................................................................................... 3
1.1 Description........................................................................................................... 3
1.2 Requirements ....................................................................................................... 3
1.3 Software Reference ................................................................................................ 3
1.4 Supported Functionality............................................................................................ 3
2 Quick Start.................................................................................................................... 4
2.1 Default Jumper and Switch Configuration....................................................................... 4
2.2 Powering the EVM.................................................................................................. 4
2.3 Software Installation and Hardware Connection Procedure .................................................. 5
3 Hardware Reference ........................................................................................................ 6
3.1 Jumper and Switch Configuration Reference ................................................................... 6
3.2 Header, Connector, and Test Point Reference ................................................................. 7
4 Software Details............................................................................................................ 11
4.1 Installing the Software ............................................................................................ 11
4.2 Connecting to the EVM Hardware .............................................................................. 13
4.3 Using the Software With the EVM .............................................................................. 13
5 EVM Bill of Materials, PCB Layouts, and Schematics................................................................. 15
5.1 Bill of Materials .................................................................................................... 15
5.2 PCB Layouts....................................................................................................... 20
5.3 Schematic .......................................................................................................... 22
List of Figures
1 Default Configurations for ADS1261 and ADS1235 EVM.............................................................. 4
2 Input Terminal Blocks ....................................................................................................... 7
3 Delta-Sigma Evaluation Engine Installation Instructions.............................................................. 11
4 Device Package Installation Instructions................................................................................ 12
5 GUI View Before Connecting............................................................................................. 13
6 GUI View After Connecting EVM......................................................................................... 13
7 Top Silkscreen.............................................................................................................. 20
8 Top Layer (Positive) ....................................................................................................... 20
9 Ground Layer (Negative).................................................................................................. 20
10 Power Layer (Negative) ................................................................................................... 21
11 Bottom Layer (Positive).................................................................................................... 21
12 Bottom Silkscreen.......................................................................................................... 21
13 ADS1261EVM Block Diagram Schematic .............................................................................. 22
14 ADS1261EVM Analog Inputs Schematic................................................................................ 23
15 ADS1261EVM ADC Main Schematic.................................................................................... 24
16 ADS1261EVM Digital Header Schematic............................................................................... 25
17 ADS1261EVM USB and Peripherals Schematic....................................................................... 26
18 ADS1261EVM Processor Main Schematic ............................................................................. 27
19 ADS1261EVM USB Power Schematic.................................................................................. 28
20 ADS1261EVM External Power Schematic.............................................................................. 29
Trademarks
Tiva is a trademark of Texas Instruments, Incorporated.
Microsoft, Windows are registered trademarks of Microsoft Corporation.
All other trademarks are the property of their respective owners.

www.ti.com EVM Overview
3
SBAU293–March 2018
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
1 EVM Overview
1.1 Description
This user guide describes the operation and use of the ADS1261 and ADS1235 evaluation module. The
EVM platform is intended for evaluating the ADS1261 or ADS1235 performance and functionality.
1.2 Requirements
1.2.1 Software Requirements
PC with Microsoft®Windows®7 or higher operating system.
1.2.2 Hardware Requirements
PC with available USB 2.0 or greater connection.
1.2.2.1 Power Supply
USB powered.
1.3 Software Reference
For the core software documentation, see the Delta-Sigma ADC EvaluaTIon Software User Manual or
navigate to the File -> About option from within the GUI, then click on the Software user guide icon.
1.4 Supported Functionality
1.4.1 Hardware Functionality
The EVM features the following hardware capabilities:
• 5-V unipolar or bipolar AVDD and AVSS supply operation
• Unipolar (5 V) and bipolar (±2.5 V) AVDD and AVSS supply operation
• 3.3-V DVDD
• Digital header for external processor or controller configuration
• Configurable for direct sensor inputs
• Onboard or external ADC clock operation
• Onboard (not installed) or external ADC voltage reference
• Fault LED for STATUS or CRC error notification
1.4.2 Software Functionality
The EVM features the following software functions:
• Device conversion control
• Device software reset
• Device power down
• Register read and write
• Conversion result readback
• Self offset and system input calibration
• Error detection through device status information
• CRC of data and SPI communication (for error prevention or detection of data transmission)

OPEN
OPEN
OPEN
RIGHT
Quick Start www.ti.com
4SBAU293–March 2018
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
2 Quick Start
This section provides a guide to quickly begin using the EVM.
2.1 Default Jumper and Switch Configuration
The EVM is configured with the settings listed in Table 2 and illustrated in Figure 1.
Table 2. Default Settings
Jumper Position Function
JP1 (Not Installed) Use onboard processor
JP2 (Not Installed) USB-derived supplies ON
JP3 (Not Installed) DVDD from USB power (1-2 connection via R94)
JP4 (Not Installed) AVDD from USB power (1-2 connection via R95)
JP5 (Not Installed) N/A
Jumper Position Function
S1 Right Unipolar analog supply (AVDD = 5 V, AVSS = 0 V)
Figure 1. Default Configurations for ADS1261 and ADS1235 EVM
2.2 Powering the EVM
The EVM is powered through the USB interface with the PC. Follow the installation and connection
procedure in Section 2.3 before connecting the EVM to the PC. Sections Section 2.2.1 and Section 2.2.2
provide additional details about the analog and digital power supply configurations of the ADC.
2.2.1 Analog Supply Configuration of the ADC'
The ADS1261 (or ADS1235) analog supply requires a 5-V source connected between the AVDD and
AVSS pins. The EVM provides onboard 5-V, 2.5-V and –2.5-V supply rails to allow for both unipolar and
bipolar supply polarities, respectively. The analog supply polarity can be selected by S1. When switching
S1, TI recommends disconnecting the USB cable from the EVM, toggling the switch, and then
reconnecting the USB cable.

www.ti.com Quick Start
5
SBAU293–March 2018
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
Use R33 to measure the AVDD supply current, by measuring the voltage drop across this resistor or by
removing the resistor and connecting a dc current meter between the "A+" and "A–" test points.
2.2.2 Digital Supply Configuration of the ADC
The ADS1261 (or ADS1235) digital supply requires a 2.7- to 5.25-V source connected between DVDD
and DGND. The EVM provides a (typical) 3.3-V onboard digital supply for the digital supply of the ADC.
R38 can be use to measure the DVDD supply current, by measuring the voltage drop across this resistor
or by removing the resistor and connecting a dc current meter between the "D+" and "D–" test points.
2.3 Software Installation and Hardware Connection Procedure
Use the following steps at startup:
1. Install the GUI software on the PC.
2. Install the device package software on the PC. (ADS1261 Device Package for the ADS1261EVM and
ADS1235 Device Package for the ADS1235EVM.)
3. Ensure all jumpers and switches are configured in the default configuration per Table 2 and Figure 1.
4. Connect the EVM to the PC using a USB cable to power the board.
5. If prompted, install any required drivers.
6. Start the GUI application on your PC. The GUI should automatically detect the connected EVM.
NOTE: After powering the EVM, the green D2, D3, and “+5V” LEDS will be lit.

Hardware Reference www.ti.com
6SBAU293–March 2018
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
3 Hardware Reference
3.1 Jumper and Switch Configuration Reference
Table 3 provides all jumper and switch configuration settings for the EVM.
(1) Switch is DPDT. Pin 1 is identified with a dot on the PCB silkscreen.
Table 3. Jumper and Switch Options
Jumper Position Description
JP1 Operation of EVM with external digital signals
Installed (ON) Hold Tiva processor (U9) in reset and disable level shifters to allow external digital
signals
Uninstalled (OFF) Normal operation with onboard Tiva processor (default)
JP2 Power down USB power supplies
Installed (ON) USB-derived power supplies disabled and powered down
Uninstalled (OFF) USB-derived power supplies enabled and ON (default)
JP3 Digital supply source
1–2 shorted Digital supply (U19) powered from USB power (default using R94 as the short)
2–3 shorted Digital supply (U19) powered from external supply source
Open No digital system power provided
JP4 5-V supply source
Installed (ON) 5-V supply powered from USB (default using R95 as the short)
Uninstalled (OFF) No analog supply powering AVDD
JP5 EXT_5V supply power down
Installed (ON) External supply regulator (U18-not installed) disabled
Uninstalled (OFF) External supply regulator (U18-not installed) enabled (default)
Switch Position Description
S1(1) AVDD and AVSS supply polarity switch
Right (pin connections:
5–6, 2–3) Unipolar supply (AVDD = 5 V, AVSS = GND) (default)
Left (pin connections: 5–4,
2–1) Bipolar supply (AVDD = 2.55 V, AVSS = –2.5 V)
S2 Tiva reset (U1 RST) button
Closed (depressed) Tiva held in RESET, level shifters (U6, U7, and U8) tri-stated
Open (normally) Normal operation
S3 Reset FAULT button
Closed (depressed) Clears FAULT indicator and writes 0x00 to the STATUS register of the ADC
Open (normally) Normal operation
S4 BSL button for Device Firmware Update (DFU) mode
Closed (depressed on
RESET) Total Tiva FLASH erasure (on reset Tiva enumerates as a DFU device)
Open (normally) Normal operation

Pin 1
Pin 2
Pin 1
Pin 2
Pin 1
Pin 2
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
J1
J3
J4
J2
www.ti.com Hardware Reference
7
SBAU293–March 2018
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
3.2 Header, Connector, and Test Point Reference
This section provides the connection information and details for all of the connectors and test points
utilized on the EVM.
3.2.1 Analog Input Terminal Blocks
Analog input to the EVM can be connected at the terminal blocks located on the left side of the board (see
Figure 2) to provide external analog signal input to the EVM for evaluation purposes. The functions for
these terminal blocks are listed in Table 4. At no time should a voltage be applied that exceeds the
absolute maximum ratings for the input of the ADS1261 or ADS1235.
Figure 2. Input Terminal Blocks

Hardware Reference www.ti.com
8SBAU293–March 2018
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
(1) J1 and J3 are not populated on the ADS1235EVM.
(2) Analog inputs are pinned out to terminal blocks through RC filters. Refer to Figure 14 for additional connection details.
Table 4. Analog Input Terminal Blocks, J1–J4
Pin Function Test Point ADS1261 Input Pin ADS1235 Input Pin
J1(1)
1 (ADS1261EVM) Analog input(2) A9 AIN9 –
2 (ADS1261EVM) Analog input(2) A8 AIN8 –
J2
1 Analog input(2) A7 AIN7 AIN5
2 Analog input(2) A6 AIN6 AIN4
3 Analog input(2) A5 AIN5 AIN3
4 Analog input(2) A4 AIN4 AIN2
5 Analog input(2) A3 AIN3 AIN1
6 Analog input(2) A2 AIN2 AIN0
7 Analog input(2) A1 AIN1 REFN0
8 Analog input(2) A0 AIN0 REFP0
J3(1)
1 (ADS1261EVM) Analog input(2) A10 AINCOM –
2 (ADS1261EVM) Reference output – REFOUT –
J4
1 GND – DGND DGND
2 AVSS – AVSS AVSS
3.2.2 External Clock
By default, a clock is supplied by the internal oscillator of the ADC when the CLKIN pin is pulled low.
However, the EVM also provides the capability to connect an external clock directly to the ADC using the
J6 connector (see Figure 16.) When connecting to J6, a direct connection can be made between pins 42
(CLKIN) and 40 (GND). A typical clock source of 7.3728 MHz (or 10.24 MHz for 40 kSPS mode, on the
ADS1261) will track with all timing shown in ADS126x Precision, 5-Channel and 10-Channel, 40-kSPS,
24-Bit, Delta-Sigma ADCs With PGA and Voltage Reference or ADS1235 High-Resolution, 24-Bit, 7200-
SPS, Delta-Sigma, Analog-to-Digital Converter With Programmable Gain Amplifier for Bridge Sensors.
NOTE: The CLKIN pin connects to the Tiva microcontroller. The microcontroller holds the CLKIN pin
low in order to enable the internal oscillator of the ADC. Before applying an external clock,
be sure to disable the GPIO output on this pin by sending the "HOLDCLOCK 0" command,
described in Table 7.

www.ti.com Hardware Reference
9
SBAU293–March 2018
Submit Documentation Feedback Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
3.2.3 Digital Interface Header
Table 5 lists the functions and pin numbers for all signals used on the digital interface.
(1) Even-numbered pins not included in this list are connected to GND.
(2) Odd-numbered pins not included are connected to the Tiva microcontroller (after passing through level shifters) but the
functionality is not used for this EVM. For connection details, see Figure 16.
(3) Signals connected to the Tiva microcontroller are named according to their respective processor pin connections. For connection
details, see Figure 16.
Table 5. Digital Interface, J6
Function ADC Side Processor Side
Signal Name Pin Number(1) Pin Number(2) Signal Name , Tiva
Connection(3)
External voltage input GND 56 55 EXT_5V
Bank3 level-shifter voltage DVDD 54 53 LVDD1
GPIO for ADC FAULT_LED 52 51 PD7
EXT_CLK 42 41 PD3 (Unused)
Bank2 level-shifter voltage DVDD 36 35 LVDD2
ADC GPIO ADC_nPWDN 34 33 PA0
SPI0 ADC_nDRDY 32 31 PA1
ADC_SCLK 30 29 PA2 (SSI0CLK)
ADC_nCS 28 27 PA3
ADC_MOSI (DIN) 26 25 PA4 (SSI0XDAT0)
ADC_MISO (DOUT) 24 23 PA5 (SSI0XDAT1)
ADC GPIOs ADC_START 22 21 PA6
ADC_nRESET 20 19 PA7
Bank1 level-shifter voltage DVDD 18 17 LVDD3 (Unused)
3.2.4 Test Points
The test points listed in Table 6 may be used to probe onboard voltage supplies and signals.
Table 6. Useful Test Points
Function Signal Name Restrictions
ADC side
Analog input (ADS1261EVM: AIN9) A9 Probe only
Analog input (ADS1261EVM: AIN8) A8 Probe only
Analog input (ADS1261EVM: AIN7, ADS1235EVM: AIN5) A7 Probe only
Analog input (ADS1261EVM: AIN6, ADS1235EVM: AIN4) A6 Probe only
Analog input (ADS1261EVM: AIN5, ADS1235EVM: AIN3) A5 Probe only
Analog input (ADS1261EVM: AIN4, ADS1235EVM: AIN2) A4 Probe only
Analog input (ADS1261EVM: AIN3, ADS1235EVM: AIN1) A3 Probe only
Analog input (ADS1261EVM: AIN2, ADS1235EVM: AIN0) A2 Probe only
Analog input (ADS1261EVM: AIN1, ADS1235EVM: REFN0) A1 Probe only
Analog input (ADS1261EVM: AIN0, ADS1235EVM, REFP0) A0 Probe only
Analog input (ADS1261EVM: AINCOM) A10 Probe only
External Bridge Supply (EXC+ positive supply) AVDD/EXC+ Remove R6 before connecting to an external
supply, consider the common mode voltage of
the ADC when selecting EXC+ voltage
External Bridge Supply (AVSS "ground" reference) AVDD For external supply ground reference only. Do
not apply a voltage to this testpoint.
External Bridge Supply (EXC– negative supply) AVSS/EXC– Remove R25 before connecting to external
supply, consider the common mode voltage of
the ADC when selecting EXC– voltage

Hardware Reference www.ti.com
10 SBAU293–March 2018
Submit Documentation Feedback
Copyright © 2018, Texas Instruments Incorporated
ADS1261 and ADS1235 Evaluation Module
ADVANCE INFORMATION
Table 6. Useful Test Points (continued)
Function Signal Name Restrictions
External reference source VIN U2–1 (VIN) Remove R27 before connecting to external
supply. Reference external supply source to
AVSS. Do not violate absolute maximum
ratings of U2.
Analog supply of the ADC (useful for current measurement) AVDD (A+) Probe only
Analog supply of the ADC (useful for current measurement) U3–4 (A–) Probe only
Digital supply of the ADC (useful for current measurement) DVDD (D+) Probe only
Digital supply of the ADC (useful for current measurement) U3–17 (D–) Probe only
5-V supply +5V Probe only
3.3-V supply +3.3V Probe only
2.5-V supply +2.5V Probe only
Ground GND Probe only
–2.5-V supply –2.5V Probe only
Processor Side
USB-sourced supply USB_VBUS
(VBUS+) Probe only
USB sourced supply USB_VBUSP
(VBUS–) Probe only
5.5-V output (U15) USB_BOOST
(+5.5V) Probe only
1.8-V output (U17) +1.8V Probe only
5.0-V output (U16) +5V Probe only
Ground GND Probe only
3.3-V output (U19) +3.3V Probe only
Step-up dc/dc converter output (U23 - not populated) HVBoost Probe only
High-voltage linear regulator output (U24 - not populated) +HVDD Probe only
Inverting dc/dc converter output (U25 - not populated) HVInvert Probe only
Negative high-voltage linear regulator (U26 - not populated) –HVSS Probe only