SX872xCEVK User Guide

SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
SX8724CEVK USER GUIDE
Evaluation Kit for SX8724C Data Acquisition System
Description
Features
The SX8724CEVK is a platform for SX8724C evaluation
and sensing application prototyping. It consists of a
single board with the ZoomingADC device interfaced to
the computer through a USB gateway.
All SX8724C I/Os are available and placed on breakout
pads for easy access. The tool is intended to be the
interface between the sensor and the PC in order to
ease the handling of the SX8724C.
Evaluation Board
•
•
•
•
•
•
Directly connects most types of sensors
Extended temperature range from -40 to 125°C
2.4V to 5.5V operation
Supply from 5V USB, externally or regulated 3.3V
USB interface with gateway to the SX8724C
On board master MCU with flash memory, access
to all IO
• Prototyping area
• I/Os, board supplies and grounds placed on pads
Graphical User Interface
•
•
•
•
Easy settings through registers and controls
System and device performance analysis tool
Save and load configurations
Log to file
SX8724C ZoomingADC System Evaluation
• Up to 16-bit differential data acquisition
• Programmable gain: (1/12 to 1000)
• Sensor offset compensation up to 15 times full
scale of input signal
• 3 differential or 6 single-ended signal inputs
• Programmable Resolution versus Speed versus
Supply current
• External reference input voltage
• Internal reference output
• Digital outputs to bias sensors
• Low-power (250 uA for 16b @ 500 S/s)
Equipment Needed
Digital Interface
PC with Windows XP or a latest version
•
•
•
•
Powered USB 2.0 port
Ordering Informations
EVK Part Number
Function
SX8724CEVK
SX8724C (I2C) Evaluation
ACS - Revision 1.0
© Semtech Corp.
May 2011
Access to I2C signal
ADC conversion ready
4 GPIO
Possibility to chain boards on the same bus
Application Examples in this User Guide
• Interfacing your first pressure sensor
Page 1
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
TABLE OF CONTENT
Section
Page
GETTING STARTED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1
2
3
4
4.1
5
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Evaluation Kit Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Board Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Software Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
About Microsoft .NET Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Board Connection and Drivers Installation (first time) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
4
5
6
7
8
HARDWARE DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6
7
7.1
8
8.1
8.2
9
9.1
10
11
11.1
Board Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
User Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Prototyping Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power Sources Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Power Supply Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
USB Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Gateway to SX8724C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
EVK Bill of Materials List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Board Physical Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Errata Note . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
GRAPHICAL USER INTERFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
12
13
13.1
13.2
13.3
13.4
13.5
13.6
13.7
13.8
14
14.1
14.2
14.3
15
16
Software Tool Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Main Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Menu Tool Bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Window Tool Bar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Status Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ZoomingADC controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Estimated Device Performances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Display Chart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Log Data to File. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ZoomingADC Data Display Window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ZoomingADC data display panel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Histogram Panel - Noise Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Measured System Performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Registers Display Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Verification Mode Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
20
20
22
23
24
28
28
30
31
32
32
33
33
35
35
APPLICATION EXAMPLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
17
17.1
17.2
17.3
Interfacing your first pressure sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pressure Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using the Evaluation Board and the GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACS - Revision 1.0
© Semtech Corp.
May 2011
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36
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
TABLE OF CONTENT
Section
17.4
17.5
17.6
17.7
17.8
17.9
17.10
Page
Reading the sensor using the GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reference Voltage Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ZoomingADC™ Configuration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ADC Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Noise Cancellation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
LSB Equivalence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ZoomingADC™ Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ACS - Revision 1.0
© Semtech Corp.
May 2011
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41
43
46
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
GETTING STARTED
1
Introduction
This section describes a typical configuration for operating the evaluation board of the SX8724C with
ZoomingADC.
The SX8724C is a signal conditioner based on Semtech's ultra low power ZoomingADC™ technology. It
directly connects most types of miniature sensors with a general purpose microcontroller.
The SX8724CEVK is a USB based evaluation tool designed to allow simple and easy evaluation of the
suitability of the SX8724C device for a given application.
The analog input signal can be entered either in differential or single ended. Refer to the datasheet for the
impact of driving an analog input in single or in differential.
2
Evaluation Kit Contents
The SX8724CEVK evaluation kit consists of:
a “Read me first” sheet
an Evaluation Board
one USB cable
a CDROM containing:
•
•
Software Installer including MS .NET framework 3.5 and USB drivers
SX8724CEVK User Guide (this document)
ACS - Revision 1.0
© Semtech Corp.
May 2011
Page 4
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
3
USER GUIDE
Board Overview
The picture below describes the main zones and functions accessible on theSX8724CEVK
USB Gateway Interface
& Power Management
Isolate/connect device
Acquisition Device
Analog Interface
& Digital Interface
Prototyping Area
Figure 1. SX8724CEVK Board Overview
ACS - Revision 1.0
© Semtech Corp.
May 2011
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
4
USER GUIDE
Software Installation
If the evaluation kit is supplied with an insert sheet, follow the instruction on the insert sheet. The latest
software revision can be downloaded on Semtech website.
1. Put the CDROM in your computer and browse the contents of the CD, open the
SX8724xEvaluationKitSetup.exe file manually. It can be found in the root of the CD-ROM. Click on Next> to
start the installation
Figure 2. Installation Screen
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
2. Choose the installation directory. The software must be installed on a local directory. Click on Next> to
confirm the path.
Figure 3. Software Install Location
3. Follow the on-screen installation guidelines until the process is completed. Please note that .NET
Framework 3.5 and the PIC USB driver will be automatically installed if not detected on your computer.
(Administrator rights may be needed).
4. The GUI software and .Net Framework are now installed on your computer.
4.1
About Microsoft .NET Framework
The Microsoft .NET Framework 3.5 is required to run the software. The software installer will install the it
automatically if not present on your computer.
Details and installation information about the .NET Framework are available on Microsoft web site (http://
www.microsoft.com). Then go to the Download section.
There are multiple versions of the .NET Framework available from Microsoft, and they can be installed side-byside on the same computer. Contact your system administrator for more details.
ACS - Revision 1.0
© Semtech Corp.
May 2011
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
5
USER GUIDE
Board Connection and Drivers Installation (first time)
1. Connect the board to the PC with the USB interface. The board is powered via the USB and will be
detected as new USB peripheral. Choose the “Install the software automatically (Recommended)” option
and click on the Next> button.
2. Windows will search for the associated driver and install the board as new peripheral.
3. Follow the on-screen installation guidelines until the process is completed. Driver compatibility screens
may appear during the installation procedure. Validate always by clicking the “Continue Anyway button”:
4. The drivers are now installed. The board and its dedicated software are ready to be used. Launch
SX8724xEVK software from the Windows Start menu.
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
USER GUIDE
HARDWARE DESCRIPTION
Board Schematic
BOARD VOLTAGE SELECTOR
POWER
VBUS
USB
GND
PGC/DPGD/D+
5
C1
C2
C5
100nF
VI N
SHDN
VOUT
C3
4.7pF
4.7pF
C4
1uF
VL DO W2
MCP1802
U3
3
F2
H2959CT-ND
1
Ferrite
F1
V SS
W4
1
2
3
4
2
VBUS
DD+
SHL D
Ferrite
J6
W1
5
VEXT
W3
VBOARD
R3
470R
D1
Re d
NC
INTERFACES
4
6
C6
10uF
C7
C8
1uF
100nF
GND
NC
VEXT
J8
2
1
PROG
GND
GND
GND
GND
GND GND
GND GND
GND GND
GND
J7
6
5
4
3
2
1
T1G
PCLK
DAT
GND
VDD
VPP
PGC/DPGD/D+
R2 0R
R1 10K
MCL R/VP P
GND
VBOARD
PICK IT Serial
PGD/D+ 19
PGC/D18
MCLR/VP P 4
OSC2
3
OSC1
2
BOOT LOADER
R4
1K
12 MHz
HC49
Wboot
2
1
C9
13
12
11
10
RB4
RB5
RB6
RB7
Y1
C10
20
GND
22pF
GND
22pF
J2
RB4/AN10/I OCB4/SDI /SDA
RB5/AN11/I OCB5/RX/DT
RB6/I OCB6/SCK /SCL
RB7/I OCB7/TX/CK
VSS
VUSB
VDD
RC0/AN4/C12I N+/INT0/Vref+
RC1/AN5/C12I N1-/INT1/VrefRC2/AN6/P 1D/C12I N2-/CVref/I NT2
RC3/AN7/P 1C/C12I N3-/PGM
RC4/P 1B/C12OUT/SRQ
RC5/CCP 1/P1A/T0CK I
RC6/AN8/SS/T13CK I/T1OSCI
RC7/AN9/SDO/T1OSCO
Acquis ition
Analog
J1
RA0/I OCA0/D+/P GD
RA1/I OCA1/D- /PGC
RA3/I OCA3/MCL R/VP P
RA4/AN3/I OCA3/OSC2/CL K OUT
RA5/I OCA5/OSC1/CL K IN
1
2
3
4
5
6
AC2
AC3
AC6
AC7
AC4
AC5
16
1
2
3
4
5
4
3
2
1
D0
D2
D3
D1
12
9
17
1
VUSB
VBOARD
16
15
14
7
6
5
8
9
RC0
RC1
RC2
RC3
RC4
RC5
RC6
RC7
VUSB
VBOARD
C11
0.47uF
GND
C12
0.1uF
GND
PIC18F14K50-E/SS
GND
INTERFACES
GATEWAY
U2
VBATT
U1
AC2
AC3
AC6
AC7
AC4
AC5
D0
D1
S X8 724C
VBATT
SCL
D3
SDA
D2
READY
VPUMP
VSS
6
14
10
13
11
VBATT
AGND
SCL
D3
SDA
D2
8 READY
15 VPUMP
7
17
VSS
W25
V_supply
C13
0.1uF
V_supply
R8 R9
10K 10K
C14
22nF
AGND
Digital
SCL
W30
SDA
W31
READY
W32
V_supply
W5
W6
W7
W8
W9
R6
W1 0
set_protocol W1 1
W1 2
W1 3
W1 4
W1 5
W1 6
W1 7
W1 8
W1 9
W2 0
W2 1
W2 2
W2 3
W2 4
AGND
ACS - Revision 1.0
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VBOARD
VBOARD
OSC1
RA5
OSC2
RA4
RA3
RC5
RC4
RC3
RC6
RC7
RB7
RB6
RB5
RB4
RC2
RC1
RC0
VUSB
RA1
RA0
GND
MCLR/VPP
RC5
RC4
RC3
RC6
RC7
RB7
RB6
RB5
RB4
RC2
RC1
RC0
VUSB
PGC/DPGD/D+
GND
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
7
USER GUIDE
User Interfaces
The analog interface gives access to the ZoomingADC inputs. The digital interface gives access to the GPIO
pins, the PC gateway connections and the power supplies. The analog and digital connections are available
on single row 2.54mm connectors and on the bare PCB next to the prototyping area.
INTERFACES
Acquis ition
Analog
J1
J2
1
2
3
4
5
6
AC2
AC3
AC6
AC7
AC4
AC5
4
3
2
1
D0
D2
D3
D1
16
1
2
3
4
5
12
9
U1
AC2
AC3
AC6
AC7
AC4
AC5
VBATT
SCL
D3
SDA
D2
READY
VPUMP
VSS
D0
D1
S X8 724C
6
14
10
13
11
VBATT
C13
0.1uF
AGND
SCL
D3
SDA
D2
8 READY
15 VPUMP
7
17
VSS
C14
22nF
AGND
Digital
Figure 4. Analog Interface Schematic
The connections points are available for industrial PCB terminal blocks and on the bare PCB next to the
SX8724C
Connect I2C interface to SX8724C
(pull-ups are on gateway side)
Connect SX8724C
VBATT pin to supply
(or measure current)
Connect SX8724C READY
signal to gateway
4C
pcb_e204v02a
Digital interface
+ Vref,in and Vref,out
Analog interface
Figure 5. SX8724C Interface on the Board
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
7.1
USER GUIDE
Prototyping Area
Using the prototyping area, one can set its own application only using the SX8724C and bypassing the
onboard gateway.
Figure 6. Prototyping Area
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
8
USER GUIDE
Power Supply
The board provides different power supply voltage possibilities; the following paragraphs describe how to
configure and use them.
8.1
Power Sources Specifications
The board can be powered through three different sources:
1. VBUS:
2. VLDO:
3. VEXT:
USB power coming from the PC.
3.3V Regulated voltage.
External source applied on VEXT interface.
Input analog voltages specified in the device datasheet.
Table 1. Power Sources Specifications
Voltage range
VBUS
Min
Typ
Max
Unit
4.5
5
5.5
V
DC, Unregulated
V
DC, Regulated
5.5
V
DC, Unregulated 2
100
mA
VLDO1
3.3
VEXT
2.4
-
Comment
Board current driving capability
1.
2.
Temperature range from -40 to 85°C
External power supply
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Evaluation Kit for SX8724C Data Acquisition System
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8.2
USER GUIDE
Power Supply Selection
Available supply voltages vs. selected power source is described below.
IMPORTANT NOTICE
- DO NEVER CONNECT VEXT JUMPER IF EXTERNAL VOLTAGE IS HIGHER THAN 5.5VDC.
- CONNECT ONLY ONE JUMPER ON THIS SELECTOR
INTERFACES
BOARD VOLTAGE SELECTOR
USB
H2959CT-ND
C4
F2
C1
C2
C3
27pF
27pF
10uF
1uF
C5
100nF
VI N
SHDN
VOUT
5
W2
VLDO
W3
VEXT
W1
VBOARD
R3
470R
ON
Re d
NC
3
MCP1802
U3
V SS
PGC/DPGD/D+
5
1
Ferrite
F1
4
GND
W4
1
2
3
4
2
VBUS
DD+
SHL D
Ferrite
J6
VBUS
C6
C7
C8
1uF
100nF
NC
GND
VEXT
J8
GND
2
1
GND
GND
GND
GND GND
GND GND
GND GND
GND
Figure 7. Power Supply Schematic
The picture below shows the selector. User should place the jumper on the desired SX8724C supply voltage
value.
Board Voltage Selectors
Enter here with an
external power supply
Power LED
Power jumper
External voltage
5V from USB
Regulated 3.3V
Board voltage
Figure 8. SX8724CEVK Power Supply Selector
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9
USB Interface
9.1
Gateway to SX8724C
USER GUIDE
The USB gateway is a complete interface to drive the SX8724C on the board. The knowledge, implementation
or modification of this gateway is not required for evaluation.
This interface is used to communicate with the GUI, but can also enable automation with external processes
such as Python, MATLAB, and LabVIEW.
R4
1K
PGD/D+ 19
PGC/D18
MCLR/VPP 4
OSC2
3
OSC1
2
12 MHz
HC49
RB4
RB5
RB6
RB7
Y1
2
BOOT LOADER
1
J9
C9
C10
GND
22pF
GND
22pF
GND
13
12
11
10
20
U2
RA0/I OCA0/D+/P GD
RA1/I OCA1/D- /PGC
RA3/I OCA3/MCL R/VP P
RA4/AN3/I OCA3/OSC2/CL K OUT
RA5/I OCA5/OSC1/CL K IN
RB4/AN10/I OCB4/SDI /SDA
RB5/AN11/I OCB5/RX/DT
RB6/I OCB6/SCK /SCL
RB7/I OCB7/TX/CK
VSS
VUSB
VDD
RC0/AN4/C12I N+/INT0/Vref+
RC1/AN5/C12I N1-/INT1/VrefRC2/AN6/P 1D/C12I N2-/CVref/I NT2
RC3/AN7/P 1C/C12I N3-/PGM
RC4/P 1B/C12OUT/SRQ
RC5/CCP 1/P1A/T0CK I
RC6/AN8/SS/T13CK I/T1OSCI
RC7/AN9/SDO/T1OSCO
17
1
16
15
14
7
6
5
8
9
VUSB
VBOARD
RC0
RC1
RC2
RC3
RC4
RC5
RC6
RC7
VUSB
VBOARD
C11
0.47uF
GND
C12
0.1uF
GND
PIC18F14K50-E/SS
Figure 9. PIC Gateway Schematic
USB interface
PICKit programmer/debugger interface
Bootloader mode control
PIC gateway
Pin access to the PIC gateway
Figure 10. PIC Gateway on the Board
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9.1.1
USER GUIDE
Bootloader Mode
The BOOT LOADER (J9) jumper allows the user to set the onboard PIC18F14K50 in bootloader mode and to
program it. One can then update the gateway with the latest driver from Semtech website or set its own
solution1 using the I2C interface (see 7.1. Prototyping Area).
By default, the jumper is not connected.
To enter in bootloader mode, shortcut the BOOT LOADER (J9) jumper and restart the PIC by unplug-plug the
SUPPLY jumper or disconnect-connect the USB cable (see Figure 10 on page 14).
9.1.2
PICkit Programming Interface
This interface is used to program the board with a Microchip PICkit 3 Programmer/Debugger.
PROG
J7
T1G
ICSPCLK
ICSPDAT
GND
VDD
VPP
6
5
4
3
2
1
PGC/DPGD/D+
MCL R/VP P
R2 0R
R1 10K
GND
VBOARD
PICK IT Serial
Figure 11. PICKIT Programmer Interface
1. Semtech does not provide support for modified Gateway software other than the official releases available on the website.
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10
EVK Bill of Materials List
Table 2.
Ref
USER GUIDE
SX8724CEVK Bill of Material
Val
Package
Description
Manufacturer
Part#
U1
MLPQ-16 4x4
SX8724C acquisition system
SEMTECH
SX8724CWLTDT
U2
SSOP-20, 6.5mm pitch
PIC Gateway
Microchip
PIC18F14K50-E/SS
U3
SOT23-5
3.3V REG LDO 300MA
Microchip
MCP1802T-3302I/OT
J6
Surface Mount, Right Angle,
Horizontal
Connector mini USB2.0
Interconnects
UX60-MB-5ST
J7
Through Hole, Right Angle
Header BRKWAY .100 6POS
R/A
Tyco Electronics
9-103325-0-06
Surface Mount, HC49/US
Crystal 12.00000 MHZ
18pF SMD
Abracon Corporation
ABLS-12.000MHZ-K4T
Steward
PZ2012D400-3R0TF
IC
Connectors
Crystal
Y1
Jumpers/selectors
W1,
W2,
W3,
Through Hole, 2.54mm
3x2 header
+ 1x RED jumper
W4,
W25,
W32
Through Hole, 2.54mm
3x 1x2 headers
+ 3x BLACK jumper
W30,
W31
Through Hole, 2.54mm
2x2 header
+ 2x BLACK jumper
SMD 0805
Ferrite 1.5A 40 Ohm
Ferrites Bead
F1, F2
Resistors
R1,
R5,
R6
10K
SMD 0603
R2
0R
SMD 0603
PICKIT prog
R3
470R
SMD 0603
LED current limiting resistor
R4
1K
SMD 0603
Protection for Bootloader
bypass
Capacitors
C1,
C2,
47pF
SMD 0603
C3
10uF
SMD 0805
C4,
C7
1uF
SMD 0603
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SX8724CEVK
Evaluation Kit for SX8724C Data Acquisition System
ADVANCED COMMUNICATIONS & SENSING
Table 2.
USER GUIDE
SX8724CEVK Bill of Material
Ref
Val
Package
C5,
C8,
C12,
C13
100nF SMD 0603
C9,
C10
22pF
SMD 0603
C11
47nF
SMD 0603
C14
22nF
SMD 0603
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Part#
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11
USER GUIDE
Board Physical Dimensions
4C
Figure 12. SX8724CEVK Board Overview
11.1
Errata Note
Boards with the PCB reference pcb_e204v02a have the MOSI and SCLK marking inverted.
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USER GUIDE
GRAPHICAL USER INTERFACE
12
Software Tool Overview
The SX8724CEVK includes a graphical user interface (GUI) that provides simplified access to all key registers
on the board. It uses intuitive controls and popup menus to write settings from the hardware.
This GUI takes high level input from the user and computes the required low level register values. With the
GUI, the user is not required to compute complicated equations to determine which values must be written
for board operation. In addition, the GUI simplifies analog interfacing by providing controls that simplify
alignment of analog functions.
The figure below illustrates the SX8724xEVK graphical user interface (GUI). Each of the numbered captions
corresponds to a proceeding chapter within the sections which correspond to the description of that GUI
feature:
1.
2.
4.
6.
7.
5.
8.
3.
Figure 13. SX872xEVK GUI Overview
1. see section 13.1. Menu Tool Bar in page 20
2. see section 13.2. Window Tool Bar in page 22
3. see section 13.3. Status Bar in page 23
4. see section 13.4. ZoomingADC controls in page 24
5. see section 13.4.5. General Controls in page 25
6. see section 13.5. Voltage Control in page 28
7. see section 13.6. Estimated Device Performances in page 28
8. see section 13.7. Display Chart in page 30
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13
Main Window
13.1
Menu Tool Bar
USER GUIDE
The Menu tool bar contains four drop down menus, File Menu, Action Menu, Tools Menu and Help Menu.
13.1.1 File Menu
Connect / Disconnect allows the connection or disconnection of the board from the host PC. This
functionality can also be accessed through the short cut buttons of the Window Toolbar (see 13.2.
Window Tool Bar).
Open Config… allows for the opening of SX8724xEVK configuration files (.cfg). This is implemented
through a standard Windows file dialog box and may also be accessed through the short cut buttons of
the Window Toolbar.
Save Config allows for SX8724xEVK configuration files (.cfg) to be saved. This is implemented through a
standard Windows file dialog box. The default file name is the last saved configuration file.
Save Config as… prompts for a new file name before saving, allowing for multiple configuration files to be
saved and may also be accessed through the short cut buttons of the Window Toolbar.
Exit closes the application.
Figure 14. File Menu Options
13.1.2 Action Menu
Reset resets the SX8724C configuration registers to the default valuesby sending an I2C General Call Reset
command.
Refresh reads all SX8724C registers and updates the GUI controls.
Show registers toggles the SX8724C Registers display window and may also be accessed through the short
cut buttons of the Window Toolbar. The register display window indicates the status of SX8724C
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USER GUIDE
configuration registers as detailed in the SX8724C datasheet. Refer to 15. Registers Display Window
section for further information.
Figure 15. Action Menu Options
13.1.3 Help Menu
Help opens a HTML help window with GUI controls descriptions.
User's Guide… opens a PDF version of the User Guide.
About… provides details of the GUI revision. The latest version of the GUI can be downloaded from
Semtech web site.
Figure 16. Help Menu Options
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13.2
USER GUIDE
Window Tool Bar
The Windows Tool Bar contains buttons that provide shortcuts to some of the functions accessed from the
drop-down menus.
Figure 17. Windows Tool Bar Menu
Open Config, USB Connect / Disconnect and Save Config buttons provides a direct control of the actions
described in 13.1.1. File Menu section. A configuration file illustrated below in Figure 18.
Reset, Refresh and Show registers provides a direct control of the actions described in 13.1.2. Action Menu
I2C address button set the I2C device address that the GUI will access.
Help button provides a direct control of the actions described in 13.1.3. Help Menu.
Figure 18. Example Configuration File Text Editor Output
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13.3
USER GUIDE
Status Bar
The Status Bar provides error messages, the onboard SX8724C version and the current user configuration file.
For further information concerning the IC revision, please refer to the SX8724C datasheet.
IC Revision Number
Message
Configuration File
Figure 19. Status Bar
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13.4
USER GUIDE
ZoomingADC controls
The ZoomingADC control sections allows the user to configure the acquisition chain of the SX8724C by
selecting the control corresponding to the desired mode. Note that the settings are applied to the device
registers as soon as the control is changed.
The representation picture on the top gives an indication of the settings applied to the ZoomingADC.
Figure 20. ZoomingADC Control Sections
13.4.1 Reference selection control
This control allows to choose the reference voltage of the acquisition chain. This can be the internally
generated VREF with a nominal value of 1.22V or VBATT (2.4V to 5.5V).
When the control selects VREF, it can also be selected combined with a GPIO to provide a reference voltage
from GPIO. See Section 13.4.7 for details.
13.4.2 Inputs controls
The controls in the group named “Inputs” lets the user choose which inputs and which reference pins will be
used to make the measurement. On this group of controls the user may also choose if the inputs are “Singleended” or “Differential” as well as choosing which of the inputs is used as “Positive” or “Negative” input.
13.4.3 PGA controls
The group of controls named “PGA” lets the user control the gain, offset and enabling disabling each PGA
individually.
The user has also the possibility to control the PGAs biasing current ratio.
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13.4.4 ADC controls
The group of controls named “ADC” lets the user control the ADC parameters. Parameters like number of
elementary conversions, the over-sampling rate, the sampling frequency at the input and the ADC biasing
current ratio can be tuned.
Select the correct input sampling frequency depending on the required input impedance and conversion
time. If necessary and/or possible, the power consumption can be reduced using the biasing parameters.
However, if the biasing current is too low, the performance of the ZoomingADC will be adversely affected.
Select the ADC parameters for the required resolution using over-sampling rate (OSR) and number of
elementary conversions (NELCONV ). Prefer over-sampling rate since it increases much faster the resolution
then NELCONV. If the offset is important, select a number of elementary conversions > 1.
The user has also the possibility to decide if the ADC will work in single shot or in continuous mode of
samples acquisition.
13.4.5 General Controls
The general control provides an indication of the status of the GPIO and settings.
Please refer to the SX8724C datasheet for a detailed description.
Figure 21. General Control
13.4.6 RC Oscillator
The RC oscillator provides the master clock reference for the chip. It produces a clock at 4 MHz which is
divided internally in order to generate the clock sources needed by the other blocks.
It can be disabled to set de device in a low power mode. Any I2C command will wake up the RC oscillator
automatically.
13.4.7 GPIO
The direction of each bit within the GPIO block (input only or input/output) can be individually set using the
GPIO controls. If direction is set as “OUT”, the corresponding pin can be set as output high or low. The digital
pins are able to deliver a driving current up to 8 mA.
D0 and D1 are multi-functional pins, see 13.4.8. Mode. for GPIO with VREF functionality.
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13.4.7.1 I2C time-out
I2C time-out provides control to enable or disable the time-out on SCL signal. If enabled, the digital interface
is reset if the SCL is low more than 30ms. This is the default mode at startup. The time-out can be disabled
with the corresponding radio button.
13.4.7.2 External Address
External address set D0 and D1 as input address bits for I2C interface. Please note that the GPIO are set as
output low at startup, so a resistor should be connected to the pad to avoid shortcut if this option is used.
Bit:
Slave address:
6 5
4
3
2
1
0
100 XX 01
Address bit[0] set to 1
D0
D1
GPIO
Address bit[1] set to 0
Figure 22. I2C Address Set Externally
When the External address option has been selected, the new I2C address of the SX8724C device must be
selected in the windows tool bar (see Section 13.2)
Figure 23. I2C Address Selection
13.4.8 Mode
Charge pump force ON and OFF allows to force ON or OFF the internal voltage multiplier to avoid
conversion interruptions due to the pump switching off and on when the VBATT supply is near 3V. Force
ON takes priority to Force OFF.
VREF chopping control allow chopping of the 1.22V internal bandgap reference. This helps to eliminate
bandgap related internal offset voltage and 1/f noise. The bandgap chop state may be forced High or Low,
or may be set to toggle during conversion at either the same rate or half the rate of the Elementary
Conversion.
Bandgap on D0 pin, outputs the SX8724C internal VREF on D0 pin. This allows external monitoring of the
internal bandgap reference or the ability to use an external reference input for the ADC, or the option to
filter the internal VREF output before feeding back as VREF,ADC input.
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VREF on D1 pin allows to select D1 pin as reference voltage for the acquisition chain. As described in
Section 13.4.1, D1 can input a VREF. When using an external VREF,ADC input, it may have any value
between 0V and VBATT.
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13.5
USER GUIDE
Voltage Control
The voltage control allows to select or read the board voltage. This allow the GUI to compute ZoomingADC
parameters and data values function of the registers settings in the GUI, for example the estimated device
performance. VBATT is read at the connection of the EVK or when the External VREF setting is changed.
Figure 24. Voltage Control
Note that the VBATT voltage or external VREF voltage are estimated according to a 1.22V bandgap reference.
For more precise data values in the GUI, the User has the possibility to set manually the real device voltage
value.
13.6
Estimated Device Performances
These data are theoretical values extracted from registers settings and computed according to the equations
available in the datasheet. The values expressed in Volt units [V] are function of the VREF voltage set by the
user (13.5. Voltage Control) in the GUI.
Figure 25. Computed Data Display
Input impedance – observed input impedance of the first PGA stage that is enabled or the input
impedance of the ADC if all three stages are disabled. Cg multiplied by gain is the equivalent gain
capacitor and Cp is the parasitic capacitor of the first enabled stage. The applied equation is:
Z in =
1
[Ω ]
(Cg ⋅ GD + Cp )
Input referred noise – the simple noise model described in the datasheet is used to estimate the equivalent
input referred rms noise VN,IN of the acquisition chain. It is computed with the extracted rms output noise
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of PGA1, 2, and 3, standard output deviation and output rms noise voltage. VN1, VN2, and VN3 are the
output rms noise figures (constants). GD1, GD2, and GD3 are the PGA gains of stages 1 to 3 respectively, set
by the user in the GUI:
2
V N, IN =
2
2
VN1 ⎞
V N2
V N3 ⎞
⎛ ---------- + ⎛ --------------------------⎞ + ⎛ ----------------⎝ GD 1⎠
⎝ GD 1 ⋅ GD 2⎠
⎝ GD TOT⎠
---------------------------------------------------------------------------------------------( OSR ⋅ N ELCONV )
[ Vrms ]
Total gain – the total gain of the acquisition chain is the product of all individual gains:
V
--V
GD TOT = GD 1 ⋅ GD 2 ⋅ GD3
Total offset – the total offset of the acquisition chain is computed according to the PGA2 and PGA3 offset
controls. Additionally, this total offset is function of the contribution of PGA3 gain. Therefore, the total
offset is computed as:
V
--V
GDoffTOT = GDoff3 + GD 3 ⋅ GDoff2
Output noise – the output noise is computed using the input noise value multiplied by the total gain of
the PGAs as follows:
V N, OUT = V N, IN ⋅ GD TOT
[ Vrms ]
Resolution – the theoretical resolution of the ADC, without considering thermal noise, is given by:
Q = 2 ⋅ Log 2 ( OSR ) + Log 2 ( N ELCONV )
[ bit ]
LSB – the least-significant bit of ADC output codes. The total range (or span) of the 16-bit ADC is 2
ratiometric to the voltage reference:
V REF
LSB = ----------16
2
16
LSBs,
[V]
TCONV – the time of the conversion sequence for one sample is computed as:
N ELCONV ⋅ ( OSR + 1 ) + 1
T CONV = -------------------------------------------------------------fS
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TELCONV – the whole conversion sequence is made of a set of NELCONV elementary incremental
conversions. The conversion time for an elementary conversion:
( OSR + 1 )
T ELCONV = ------------------------fS
[s]
Sample rate – the ADC output sample rate is computed with the TCONV time:
1
samplerate = ---------------T CONV
13.7
[ Hz ]
Display Chart
The display chart is a graphic representing the ADC output samples. An enlarged graph including a histogram
and measured system performance is available when pressing the button and is described in 14.
ZoomingADC Data Display Window section.
Figure 26. Display Chart
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13.8
USER GUIDE
Log Data to File
Set the Log selector to ON to access the Log control:
Figure 27. Log Controls
Max sample input box indicates how many ZoomingADC samples are stored in the log file.
Browse... button let the user choose where to store the log file and which name it will have.
Start/Stop start the logging process or stop it. While the logging process is running a progress bar will
show the progress.
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14
USER GUIDE
ZoomingADC Data Display Window
The windows described in this section are only accessible for enabled configurations in the GUI.
Figure 28. ZoomingADC Data Display Window
14.1
ZoomingADC data display panel
By default, the samples are displayed in the panel in a range from -32768 to 32767 LSB.
Various options allows the user to display the small signals as described below. Note that the following panel
options are available in the small display chart described in 13.7. Display Chart.
14.1.1 Zoom (left click on the panel)
If the user draws a rectangle in the graphic and then release the mouse button the graphic will zoom the
signal inside the rectangle.
14.1.2 Zoom and Pan Via Mouse Scroll
The mouse scroll (if available) can be used to pan or zoom. It zooms in when you spin the scroll towards you
and zooms out when you spin it towards the display panel. Holding it pushed also enables the pan command.
To reset the display to default range, the right button of the mouse provides the Undo All Zoom/Pan operation
(see Section 14.1.3.)
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14.1.3 Display Options (right click on the panel)
Copy... allows the user to copy the display panel into the clip-board. Then the curve can be past in any
other program.
Save Image As... allows to save the display panel into various common picture formats.
Page Setup... provides the settings for printing the panel
Print... allows to select an installed printer and print the display panel.
Show points Values displays the sample value by pointing on any location on the curve.
Un-Zoom allows the user to zoom out (with a small step) the display panel if the wheel is not available.
Undo All Zoom/Pan resets the display range to it’s default values.
14.2
Histogram Panel - Noise Analysis
The distribution of the codes from the acquired signal can be seen on the Histogram panel.
The Histogram graph is computed from a buffer of 1000 consecutive samples. Therefore, the refresh rate is
dependant of the sample rate. If the signal is DC, the distribution width shows the noise.
The samples are coded on 16 bits, if the digital resolution is set to lower than 16bits, some output codes will
never be hit.
14.3
Measured System Performances
The right value for the Measured System Performances is correct only when the DC signal is applied on the
inputs. The values expressed in Volt units [V] are function of the VREF voltage set by the user (13.5. Voltage
Control) in the GUI.
The measured system performances are computed as follows:
Average– average of the code distribution measured on a buffer of 1000 samples. If the input is 0V, the
average is equal to the output offset:
1
μ = ---- Σ ( samples )
N
[ LSB ]
Standard Deviation – the standard deviation is the rms value (Root Mean Square) of the code distribution:
σ =
12
--Σ ( sample – average )
N
[ LSB ]
Output noise – the output noise rms VN,OUT is computed with the standard deviation of the code
distribution:
V REF
V N, OUT = σ × ----------16
2
[ Vrms ]
Input referred noise – VN,IN is the rms noise referred to the input. This parameter is computed from the
output rms noise (code) and the total PGA gain:
V N, OUT
V N, IN = ----------------GDtot
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Noise Density (referred to the input) – the input noise density VND,IN is computed according to sample rate
previousely computed in the software with OSR, NELCONV and fs parameters:
V N, IN
VND, IN = ---------------------------------samplerate
Vrms
------------Hz
ENOB DC – Effective Number Of Bits (or Effective Bits) 1– is computed according to the σ samples rms
noise value. This value is a DC ENOB measure, not the dynamic ENOB that is measured using FFT and
SINAD. Its equation is as follows:
ENOB = 16 – Log 2 ( σ )
[ bits ]
NFR – the Noise Free Code Resolution (or flicker-free resolution) is the number of bits of resolution beyond
which it is impossible to distinctly resolve individual codes. Multiplying by a factor of 6.6 converts the
samples rms noise into a useful measure of peak-to-peak noise:
NFR = 16 – Log 2 ( σ ⋅ 6.6 )
[ bits ]
1.Digital averaging increases resolution and reduces noise. The effects of input-referred noise is reduced by digital averaging on the
buffer of samples used to compute the Measured System Performances. Therefore, the ENOB DC value can be higher than the sample
width limitation (>16 bits).
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15
USER GUIDE
Registers Display Window
As outlined in Section 13.2. Window Tool Bar the SX8724x GUI has a show registers utility that, when
enabled from either the Menu or Windows tool bar, provides details of the status of all configuration registers
that are documented in the SX8724C datasheet.
Whenever the contents of a register are changed in the main GUI window, the corresponding register
displays the new contents of the register(s), highlighting changed contents in red for a period of
approximately 5 seconds before reverting back to black.
The register window is displayed below in Figure 29.
Figure 29. SX8724x Registers Display Window
16
Verification Mode Window
When no board is connected to the PC, launching the application results in the GUI display being grayed out
and the user is unable to enter data.
By depressing the <CTRL>+<ALT>+<N> keys of the PC keyboard simultaneously, the user can write to the
configuration registers to verify propose settings, as well as load and save configuration files (*.cfg).
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APPLICATION EXAMPLES
17
Interfacing your first pressure sensor
17.1
Introduction
This chapter intends to show how to interface a pressure sensor using the SX8724CEVK evaluation board.
It also shows how to use efficiently the ZoomingADC™ of the SX8724C and demonstrate the benefits of the
zooming feature.
17.2
Pressure Sensor
The chosen sensor for this application is a 200kPa absolute pressure sensor type MPX2202AP by Freescale.
Its main characteristics are described in the table below:
Table 3. Sensor main characteristics
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Characteristic
Value (Typ)
Unit
Pressure range
0-200
kPa
Supply voltage
3.3
Vdc
Supply current
3.3
mAdc
Full scale span
3.3
mVdc
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17.2.1 Sensor Pinout & Schematic
3
VS
Vout+ 2
Sensing
Element
4
3
2
1
Vout- 4
GND
1
PIN 1
Figure 30. Pressure sensor pin out & equivalent schematic
17.2.2 Sensor Transfer Function
The transfer function of the sensor is given in the figure below. It shows the output voltage (min., typ. and
max.) as a function of the absolute input pressure for the specified supply voltage.
16
Sensor output Voltage vs Pressure @ 3.3V supply
14
Min
Typ
Max
Output Voltage [mVDC]
12
10
8
6
4
2
0
0
20
40
60
80
100
120
140
160
180
200
-2
Pressure [kPa]
Figure 31. Sensor transfer function
Note: The given transfer function in the datasheet is for a 10V power supply, here the transfer function was
translated for a 3.3V power supply.
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17.2.3 Sensor Connection to the SX8724C
The schematic below shows how the sensor is connected to the SX8724C using the pins AC2–AC3 as
differential input. The default VMUX setting will select VBATT–VSS as reference inputs for the acquisition chain.
The sensor will be biased with VBATT when D0 is set as digital output high state. It will be switched on/off by
the register setting.
VBATT
BIAS
D0
VSS
Vs
AMUX
VOUT+
VOUT-
VIN
VSS
VREF
AC3
AC2
±Vin
S
GND
VD1
PGA1
VD2
VIN,ADC
±Vin
±Vin
±Vin
±Voff PGA2
±Voff PGA3
±Vref
ADC
Analog Inputs
Reference Inputs
VREF,ADC
VBATT
VSS
VREF
VSS
VMUX
ANALOG ZOOM
Figure 32. Sensor schematic connection to the SX8724C
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17.2.4 Sensor Connection to the Board
The picture below shows how to connect the sensor on the evaluation board, each red point represents a
connection.
pcb_e204v02a
4: Vout3: Vb
2: Vout+
1: GND
PIN 1
4
Figure 33. Connection on the SX8724CEVK Evaluation board
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17.3
USER GUIDE
Using the Evaluation Board and the GUI
17.3.1 Configuration
1. Connect the sensor to the board as described in Figure 33 on page 39.
2. Select the power supply of the evaluation board to 3.3V (see chapter “Power Supply Selection” on
page 13 of the evaluation board user’s guide).
3. Connect the USB connector to the evaluation board and to the PC to power the board.
4. Launch the Graphical User Interface.
5. Start the connection to the EVK in the GUI.
17.3.2 Voltages Settings
In the “Voltages” group of controls, set the VBATT value to the corresponding value selected on the board:
3.3V. This has no influence for the board itself but allows correct data calculation in the GUI.
Figure 34. “Voltages” settings in the GUI
17.3.3 Sensor Biasing
After a Power-on-reset the GPIO are set to a digital output low state. The sensor bias is connected to D0 pin.
Switch ON the “D0” “Out” control to set this GPIO as output high state to drive the sensor.
Figure 35. “GPIO” settings
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17.4
USER GUIDE
Reading the sensor using the GUI
By default, if no configuration file is loaded the SX8724C state should look like in the picture beside.Press the
“Set Default” button to start a default continuous acquisition mode to enable the acquisition chain.
Press the Set Default button here
Figure 36. SX8724C default state
17.5
Reference Voltage Selection
After having pressed the “Set Default” button as described in "17.4 Reading the sensor using the GUI", the
GUI sets the input reference (VMUX) to VREF (VREF-VSS). Change this and select VBATT as voltage reference for
the acquisition chain. The “Reference” configuration control should look like the picture below
Figure 37. Reference Voltage Selection
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17.5.1 Inputs Configuration
Select the AC3-AC2 analog inputs in differential mode as input chanel. The “Inputs” configuration controls
should look like the picture below
Figure 38. SX8724C “Reference” and “Inputs” Groups of Controls
Note: Function of the layout and the used sensor, to avoid crossing sensor Vout+ and Vout- on a board the
SX8724C allows inverting the polarity of the inputs we will use the “sign inversion” feature during SX8724C
configuration.
17.5.2 Rough Gain Configuration
As the transfer function shows, the total span of the sensor is 14.5mV and the total span of the ZoomingADC
is 3.3V (VBATT ).
The gain that needs to be applied to see the full range of the signal is then calculated as follows:
Gain =
ADCOut Max
3300mV
=
= 227
SensorOut Max 14.5mV
Equation 1
This means PGA1 gain GD1=10, PGA2 gain GD2=10 and PGA3 gain GD3=2.25 (granularity of PGA3 = 1/12).
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The “PGA” controls should then look like the picture below.
Figure 39. SX8724C“PGA” Group of Controls Configuration
17.6
ZoomingADC™ Configuration
17.6.1 Zooming on the Signal
As the sensor is supposed to work at the atmospheric pressure (max: 107.8kPa - min: 88.7kPa) we will zoom
on around these values and thus use the maximum amplification as possible to get the full signal at the ADC
input.
As for zoom in pictures we set a particular zone of interest called measuring window (in red below).
16
Sensor output Voltage vs Pressure @ 3.3V supply
14
ADC input sensor voltage vs pressure
Min
1600
12
Typ
Max
1400
Voltage[mVDC]
Output Voltage [mVDC]
1800
Min
Typ
Max
10
8
6
4
1200
1000
800
600
2
400
Measuring window
0
200
-2
0
0
20
40
60
80
100
120
140
160
180
89
200
91
Pressure [kPa]
93
95
97
99
101
103
105
107
Pressure [kPa]
Figure 40. Zooming on the Signal
17.6.2 Gain Computing
To compute the total gain that must be applied to the sensor output signal we must know 2 parameters:
1. The maximum output span of the ADC, here 3.3V
2. The maximum output span value of the sensor in the measuring window, here around 8.5-4.5 = 4mV
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Now we can apply the following formula to get the gain:
Gain =
ADCOut Max
3300mV
=
= 825
SensorOut Max
4mV
Equation 2
As the total gain is more than 100, all PGAs have to be enabled to obtain a total amplification of 825. The
gains must be set as follow:
• PGA1 = 10
• PGA2 = 10
• PGA3 = 8.25
17.6.3 Offset Cancellation
The offset computation uses the middle sensor output value at the ZoomingADC™ input as shown in the
formula below:
Offset =
MwMax − MwMin 8.5mV − 4.5mV
=
= 6.5mV
2
2
Equation 3
Note: Mw stands for measuring window.
Offset removing PGA after PGAs:
PGA1: Amplified sensor output = 6.5mV x 10 = 65mV
PGA2: Amplified sensor output = 65mV x 10 = 650mV
Offset cancellation: min +/- 0.2 x VREF (3.3V x 0.2 = 660mV).
-> The minimum value is too big we cannot use the offset cancellation of PGA2.
PGA3: Amplified sensor output = 650mV x 8.25 = 5362mV
Offset cancellation: min +/- 1/12 x VREF (1/12 x 3.3V = 275mV)
-> The minimum value fits up to 19 times in 5362mV 19/12 x 3.3 = 5225mV.
Note: 19/12 = 1.583
17.6.4 Final Gains Configuration
As computed, the PGA gains can be raised to 825.
The offset is 19/12 (see “Offset Cancellation” on page 44), as the input signal and the reference are noninverted, the offset has to be positive.
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The “PGA” group of controls should then look like as picture beside.
Figure 41. SX8724C “PGA” final configuration
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17.7
USER GUIDE
ADC Configuration
The following PGA and ADC set-up is chosen to implement the measurement window. With this set-up, the
input voltage range of the circuit corresponding to the full scale output code range is 4.5mV to 8.5mV. This
window is represented in Figure 40.
16
Sensor output Voltage vs Pressure @ 3.3V supply
ADC input sensor voltage vs pressure
Min
1600
12
Typ
Max
1400
Voltage[mVDC]
Output Voltage [mVDC]
1800
Min
Typ
Max
14
10
8
6
1200
1000
800
4
600
2
400
0
200
-2
0
20
0
40
60
80
100
120
140
160
180
89
200
91
93
95
Pressure [kPa]
97
99
101
103
105
107
Pressure [kPa]
VBATT
BIAS
D0
VSS
Vs
AMUX
VOUT+
VSS
VREF
AC 3
AC 2
VOUT -
VIN
VD1
±Vin
±Vin
±Vin
±Vin
±Voff PGA2
±Voff PGA3
±Vref
S
GND
PGA1
VD2
VIN,ADC
ADC
Analog Inputs
Reference Inputs
VREF,ADC
VBATT
VSS
VREF
VSS
VMUX
ANALOG ZOOM
Figure 42. PGA Parameters
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Table 4. ADC Configuration
Characteristic
Value (Typ)
Unit
VBATT = VREF
3.3
V
Sampling frequency
250
kHz
Gain of PGA1
10
V/V
Gain of PGA2
10
V/V
Gain of PGA3
8.25
V/V
Total PGA gain
825
V/V
Offset of PGA2
0.00
VREF
Offset of PGA3
1.58
VREF
Total equivalent input offset
6.33
mV
Over-sampling rate
512
Elementary conversions
2
Resolution1
16
bit
Conversion time
4.108
ms
LSB equivalent input voltage
62.47
nV
Equivalent input noise2
649E-09
Vrms
PGA settling time
2.048
ms
1.
2.
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17.8
USER GUIDE
Noise Cancellation
The OSR and NELCONV parameters can be increased in order to reduce the noise generated by the ADC and
PGAs.
Noise with OSR=512, NELCONV=2:
Noise with OSR=1024, NELCONV=8:
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17.9
USER GUIDE
LSB Equivalence
Using the defined ADC and PGA set-up, an equivalent input pressure per LSB can be calculated. Using the
typical sensor transfer function, we obtain:
VLSB ⋅ pressureRange
⋅ 200kPa- = 63nV
-----------------------------------= 0.96Pa
Pressure = ------------------------------------------------------sensorVoltageRange
13.04mV
Equation 4
The approximate equivalence between Pressure and altitude is defined as follow:
0.96Pa ⋅ 8620m
Altitude = 100kPa ≡ 8620m → --------------------------------------- = 0.0079Pa
100kPa
Equation 5
This implementation has a resolution of 8cm altitude.
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17.10 ZoomingADC™ Benefits
Now that we zoomed on the signal, we can compare the zoom performances with and without the offset
compensation. To make a comparison do as follow:
Without Zoom (gain only)
1. On the graph, set the full scale view: right click on the panel and select Undo All Zoom/Pan option to reset
the display range to the default full scale range.
2. Set the configuration to Gain = 225 & no offset cancellation as in 17.5.2. Rough Gain Configuration
section.
3. Then blow in the sensor tube (try to make the maximum signal span).
The signal span correspond to 31923–28599 = 3324 bits. The result should look like the picture below:
3324 bits span
Figure 43. Signal Span Using Rough Gain Setting
With Zoom (gain and offset)
Now set the parameters as defined in 17.6.4. Final Gains Configuration (Gain 825, offset -1.58 x VREF). The
result should look like the picture below:
10’370 bits span
Figure 44. Signal Span Using Zooming Settings
The signal span is 11743–1374=10370 bits which corresponds to a 320% gain on the signal reading
allowing you to have more consistent readings.
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