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[FAQ] FDC2x1x Capacitive Sensing FAQs

Other Parts Discussed in Thread: FDC1004, FDC2214, LDC1101, LDC1612, LDC1312, TIDA-00317, TIDA-00373, TIDA-00506, TIDA-00220, TIDA-01409, TIDA-00466, FDC1004EVM, FDC2114EVM, FDC2114, FDC2214EVM, ENERGIA, FDC2212, FDC2112

FDC2x1x Capacitive Sensing FAQs

 For additional information, please see the FDC1004 Capacitive Sensing FAQs: https://e2e.ti.com/support/sensors/f/1023/t/976381

What are the differences between Capacitive Sensing Versus Capacitive Touch Solutions.

Texas Instruments provides solutions for capacitive sensing and capacitive touch applications, which share some important similarities and some crucial differences. Capacitive sensing applications can require relatively large target distances and/or higher resolution than capacitive touch applications.

The table below offers a brief comparison between the similarities and differences between these two applications

Requirements

Capacitive Sensing

Capacitive Touch

Channel count

Low (< 4)

High (> 8)

Resolution

High

Low

Typical distance

Up to 70 cm

2 to 3 mm

Sensitivity

< 1 fF

10s to 100s fF

Requires contact

No

Yes

Power consumption

μA range

μA to mA range

For more information on capacitive touch solutions, please consider TI's capTIvate as the best fit for this application.

·         http://www.ti.com/microcontrollers/msp430-ultra-low-power-mcus/capacitive-sensing-mcus-overview.html

                                

What applications can/can’t be supported by capacitive sensing?

  1. Liquid Level Sensing
    For most non-conductive liquid level sensing applications (including water), the FDC1004 should be used. The FDC1004 has an active shield driver which helps the system against interference from environmental factors.


  2. Non-Metal Proximity Sensing
    The FDC1004 is the best choice, since the FDC2x1x does not have a shield driver, can and requires advanced system level expertise.


  3. What applications do not work with TI's capacitive sensing technology?
    Metal detection - to detect metal, TI's inductive sensing solutions are a better option.
    See the TI E2E Inductive Sensing FAQ  Inductive Sensing FAQ

 

How do I get started with Capacitive Sensing?

A list of learning and design resources, sorted by subject, are given below.

Subject

App Note Title

App Note URL

Introductory App Notes

Common Inductive and Capacitive Sensing Applications

https://www.ti.com/lit/pdf/slya048

Basics of Capacitive Sensing with FDC1004

 https://www.ti.com/lit/pdf/snoa927

Liquid Level Sensing App Notes

Capacitive Sensing: Ins and Outs of Active Shielding 

https://www.ti.com/lit/pdf/snoa926

Capacitive Sensing: Out-of-Phase Liquid Level Technique

https://www.ti.com/lit/pdf/snoa925

Capacitive Sensing: Direct vs Remote Liquid-Level Sensing Performance Analysis

https://www.ti.com/lit/pdf/snoa935

Liquid Level Sensing with the Immersive Straw Approach

https://www.ti.com/lit/pdf/snoa934

How to Calibrate FDC1004 for Liquid Level Sensing Applications

https://www.ti.com/lit/pdf/snoa958

Proximity sensing

Capacitive Proximity Sensing Using the FDC1004

https://www.ti.com/lit/pdf/snoa928

Capacitive Proximity Sensing Using FDC2x1y

https://www.ti.com/lit/pdf/snoa940

General App Notes, Technical Articles and Blogs

Derivative Integration Algorithm for Proximity Sensing

https://www.ti.com/lit/pdf/snoa939

Ground Shifting in Capacitive Sensing Applications

https://www.ti.com/lit/pdf/SNOA952

Power Reduction Techniques for the FDC2214/2212/2114/2112 in Capacitive Sensing Applications

https://www.ti.com/lit/pdf/SNOA943

Capacitive sensing: simple algorithm for proximity sensing

https://e2e.ti.com/BLOGS_/B/ANALOGWIRE/ARCHIVE/2015/11/23/CAPACITIVE-SENSING-SIMPLE-ALGORITHM-FOR-PROXIMITY-SENSING

Capacitive sensing: which architecture should you choose?

https://e2e.ti.com/blogs_/b/analogwire/archive/2015/10/20/capacitive-sensing-which-architecture-should-you-choose

Inductive Sensing App Notes with Useful Info for Capacitive Sensing Circuits using the FDC2x1y

Measuring Rp of an L-C Sensor for Inductive Sensing

https://www.ti.com/lit/pdf/snoa936

Optimizing L Measurement Resolution for the LDC161x and LDC1101

https://www.ti.com/lit/pdf/snoa944

Setting LDC1312/4, LDC1612/4, and LDC1101 Sensor Drive Configuration

https://www.ti.com/lit/pdf/snoa950

TI Designs

Capacitive Based Liquid Level Sensing - TIDA-00317 (FDC1004 , MSP430F5528 )

http://www.ti.com/tool/TIDA-00317

Backlight and Smart Lighting Control by Ambient Light and Proximity Sensor Reference Design - TIDA-00373 (FDC1004 , HDC1000 , HDC1008 )

https://www.ti.com/tool/TIDA-00373

Automotive Capacitive Proximity Kick to Open Detection Reference Design TIDA-00506 (FDC1004)

https://www.ti.com/tool/TIDA-00506

Capacitive-Based Human Proximity Detection for System Wake-Up & Interrupt Reference Design - TIDA-00220 (FDC1004 , LM3630A , LP5907 )

https://www.ti.com/tool/TIDA-00220

Automotive Capacitive Kick-to-Open Reference Design - TIDA-01409

(FDC2212-Q1 , SN74LVC1G04-Q1 , TPS7B69-Q1 )

https://www.ti.com/tool/TIDA-01409

Noise-immune Capacitive Proximity Sensor System Reference Design - TIDA-00466

(FDC2212 , FDC2214 , CSD25310Q2 )

https://www.ti.com/tool/TIDA-00466

EVMs

FDC1004EVM - 4 Channel Capacitive to Digital Converter Evaluation Module

https://www.ti.com/tool/FDC1004EVM

FDC2114EVM - FDC2114 with Two Capacitive Sensors Evaluation Module

https://www.ti.com/tool/FDC2114EVM

FDC2214EVM - FDC2214 with Two Capacitive Sensors Evaluation Module

https://www.ti.com/tool/FDC2214EVM

Software

Capacitive Sensing Sample Code (Energia)

http://www.ti.com/lit/zip/snvc187

Sensing Solutions EVM GUI Tool

http://www.ti.com/lit/zip/snoc028

FDC211x/FDC221x Current Consumption Estimator

http://www.ti.com/lit/zip/snoc033

 

 

 

 

What are the differences between the FDC1004 and the FDC2212/2214?

The table below shows & compares the major features of the two devices.

FDC2212/2214

FDC1004

Number of Channels

2 or 4

4

Architecture

Resonant LC Tank

Switched Cap

Supply Voltage

3.3

3.3

I active

2.1mA

0.95mA

Sensor Current

6mA

0

Sensor driving Frequency

0.1Mhz - 10 MHz

25 kHz

Maximum Sensor Input

250nF @ 10Khz / 25pF @ 10 MHz

115pF

Sensor input range w/respect to input offset calibration

NA

±15pF

Input Offset Calibration

N/A

100pF

Integrated Shield Driver

N/A

400pF

Driver Architecture

Discontinuous Sin Driver

Continuous CLK driver

Effective resolution

12/28 bits depending on the LC frequency

16 bits

Gain error

N/A

0.20%

Gain Error over temp

Depends on External LC

37.5 ppm/C

DC PSRR

N/A

13.6fF/V

EMI

Poor, needs external passives

Better

Configurability

High SW and HW

Contained

Package

QFN

QFN/TSSOP

 

  • As the table shows, the FDC1004 input is a switch-cap topology while the FDC2x12/4 uses a resonant tank. The major advantages of the FDC1004 is its integrated shield driver, which can improve the EMI/noise immunity of your circuit, and its driver architecture, which greatly reduce EMI emissions, compared to the FDC2x12/4.

 

 

FDC2x1x frequently asked questions:

  • When is the FDC2x1x a bad fit for my capacitive sensing application?
     The FDC2x1x family of devices uses a resonant LC tank topology instead of the traditional switched capacitor architecture. It also does not include a dedicated shield driver pin. For this reason, usually FDC1004 is the better choice for liquid level sensing applications. For other types of capacitive sensing, TI's capTIvate family is the better choice.
    The main challenges for the FDC2x1x are:
  1. Requires an external inductor for each channel.
  2. Poor EMI/EMC performance
  3. Difficult to tune for different systems

 

  • Can the FDC2x1x be used for proximity detection?
    The FDC2x1x family of devices can be used for proximity detection, with the caveats discussed just above. For more information, please see the app note Capacitive Proximity Sensing Using FDC2x1y, https://www.ti.com/lit/pdf/snoa940
  • Which FDC2x1x device should I use?
  1. Determine the number of channels needed for your system
  2. For precision applications, start with the FDC221x family of devices for initial evaluation. The FDC211x, lower resolution devices are pin for pin compatible and can be tested after suitability with the higher resolution device is proven. 

 

FDC2212

FDC2112

FDC2214

FDC2114

Resolution

28 bits

12 bits

28 bits

12 bits

Number of channels

2

2

4

4

 

  • What is the effective resolution of the FDC221x?
    While the following app note focuses on inductive sensing: http://www.ti.com/lit/pdf/snoa944.
    The concepts explained for the LDC161x devices also apply to the FDC221x.
  • How do I choose the IDRIVE setting for the FDC2x1x?
    While the following app note focuses on inductive sensing (http://www.ti.com/lit/pdf/snoa950), the concepts explained for the LDC161x and LDC131x also apply to the FDC2x1x.
  • How can I improve EMI/EMC performance with the FDC2x1x?
    The passive filtering and supply/return routing recommendations from the following app note are applicable to the FDC2x1x:   http://www.ti.com/lit/an/snoa962/snoa962.pdf
  • How can the FDC2x1x power consumption be reduced?
    Device power consumption can be reduced with duty-cycling and clock-gating techniques. Details are available in the app note Power Reduction Techniques for the FDC2214/2212/2114/2112 in Capacitive Sensing Applications https://www.ti.com/lit/pdf/SNOA943