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NXP Semiconductors
User's Guide
KE15Z Touch Sensing Interface
1. Introduction
The purpose of this document is to explain the new TSI
(Touch Sensing Interface) measurement and how to
develop the software and hardware board from the
application point of view.
2. TSI Methods
Touch sensing interface (TSI) provides touch sensing
detection on capacitive touch sensors. The external
capacitive touch sensor is typically formed on PCB and
the sensor electrodes are connected to TSI input
channels through the I/O pins in the device.
KE15Z TSI supports 2 kinds of touch sensing methods,
the self-capacitive mode and the mutual-capacitive
mode, as showing in the figure below.
the self-capacitive mode, and
mutual-capacitive mode.
© 2016 NXP B.V.
Figure 1
shows
Figure 2
shows the
Document Number: KE15ZTSIUG
Contents
1.
Introduction ........................................................................ 1
2.
TSI Methods ....................................................................... 1
2.1.
Self-capacitive mode ............................................... 2
2.2.
Mutual-capacitive mode .......................................... 5
3.
TSI software configurations ................................................ 7
3.1.
Self-capacitive mode configurations ........................ 7
3.2.
Mutual capacitive mode configurations ................. 14
3.3.
Q&A for software configurations .......................... 17
4.
Hardware design guide ..................................................... 18
4.1.
Electrode shapes .................................................... 18
4.2.
PCB trace routing .................................................. 19
4.3.
Ground plane ......................................................... 20
4.4.
Electrodes placement ............................................. 21
4.5.
Hardware checklist ................................................ 21
5.
References ........................................................................ 22
6.
Revision history ................................................................ 22
Rev. 0 , 12/2016
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Summary of Contents for NXP Semiconductors KE15Z
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Page 1: Table Of Contents
TSI input References ................ 22 Revision history ..............22 channels through the I/O pins in the device. KE15Z TSI supports 2 kinds of touch sensing methods, the self-capacitive mode and the mutual-capacitive mode, as showing in the figure below. Figure 1... -
Page 2: Self-Capacitive Mode
The self-capacitive mode requires single pin for each touch sensor and measures the capacitance on an electrode connected to a single TSI channel. It then converts the capacitance into a digital count by driving average current on the electrode and measuring the charge/discharge times. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... - Page 3 Block diagram of TSI self-capacitive mode The following figure shows the timing of TSI measurement for the self-capacitive mode. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 4 Attached below is the definition of the sensitivity: KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
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Page 5: Mutual-Capacitive Mode
One of the TSI channels is used as transmit (TX) channel and the other one is used as receive (RX) channel. Figure 6 shows the connections of TSI channel in mutual-capacitive mode. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... - Page 6 • Vp, Vm: configurable, dual reference voltage which can be configured by DVOLT<1:0>. ���� • ∆��: signal voltage Rx received, decided by VDD × , Cm is the mutual-capacitance, Cs is ����+���� KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
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Page 7: Tsi Software Configurations
The software configurations for the self-capacitive mode include: clock generation scan time comparator sensitivity boost Attached below is an example of the configurations for the self-capacitive mode. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... - Page 8 Attached below is the formula of the basic clock generation, when TSI_SSC0[SSC_MODE] = 10b. ������������������ SwitchingClock = �������������� Main clock setting Setting: Main Clock Register Value Main Clock(MHz) 20.72 16.65 TSI_MODE[SETCLK] 13.87 11.91 KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 9 ������������ℎ��������ℎ(��1) + ������������ℎ��������������������ℎ(��2) + ��������������������ℎ(��3) *When TSI_SSC0[SSC_MODE] = 00, the SSCHighRandomWidth can be random(PRBS). Figure below shows the timing of the switching clock generation. Timing of the Advance Clock Generation with SSC enabled KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 10 . When the decimation is set to 0 (only once), the single scan is engaged. The 16-bit counter accumulates all scan results until the scan number reaches predefined number, and users can read TSI_DATA[TSICNT] to get the final scan result. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 11 Example 10, is recommended. Change the order to 2, then the final scan result becomes 161*64=10304, but TSI only performs scan for 8*2=16 times, and the scan time is 2480us, saving a lot of time by setting order =2. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 12 TSI Scan Time / Conversion Result(Counter) 6000 4937 5000 4000 3000 2480 2000 1253 1000 1288 2576 5152 TSI Conversion Result(Counter) KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 13 Cremoved increases, the sensitivity becomes better, which means it’s easier to recognize touch event. Sensitivity Boost / Key Configuration TSI Channel 12 80.0% 66.9% 60.0% 30.2% 40.0% 19.4% 11.9% 10.5% 20.0% 0.0% 10.0 Key Configuration: Capacitance Removed (pF) KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
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Page 14: Mutual Capacitive Mode Configurations
One difference to the self-mode clock, the SSC must be enabled for mutual mode to generate switching clock, because the TSI Rx signal in the mutual mode depends on the TSI_SSC0[CHARGE_NUM](i.e. t3) as showing in the figure below. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... - Page 15 1us. Similar to the self-mode configurations, the mutual mode also support multiple scan per channel, and the scan number is configured by TSI_SINC [DECIMATION], [ORDER], and [CUTOFF]. Please refer to the chapter of self-mode scan time for the detailed descriptions. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
- Page 16 From the configuration above, we can find out that the boost current is the key configuration to the sensitivity boost feature, as the boost current increases, the sensitivity becomes better, which means it’s easier to recognize touch event, as showing in the figure below. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors...
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Page 17: Q&A For Software Configurations
A: The bit of M_MODE determines the Rx signal received from Tx channel, as showing in the figure below. Setting M_MODE as 0 (i.e. -5V ~ +5V) is recommend as it’s more energy efficient. Setting M_MODE KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... -
Page 18: Hardware Design Guide
Customer should select the right finger numbers for the thickness of touch overlay. For example, if the touch overlay is 3mm in thickness, 4 fingers is the best choice. If the touch overlay is 2mm in thickness, 5 fingers is ok. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... -
Page 19: Pcb Trace Routing
• Avoid routing under touch electrode, do not route traces directly under any touch pad. • For the mutual mode key, keep the Tx trace as far as possible from the Rx trace. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... -
Page 20: Ground Plane
2 mm. For example, a PCB layout for a system with a 1-mm overlay should have a 1-mm annular gap, while a 3-mm overlay design should have a 2-mm annular gap. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... -
Page 21: Electrodes Placement
• GND return path is provided per specifications (GND hatch below or at least around the electrode keypad). • No pull-ups present in TSI-enabled (touch sensing input module) pins. KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... -
Page 22: References
Following references are available on NXP website. 1. Designing Touch Sensing Electrodes (Document: AN3863) 2. KE15Z Reference Manual (Document: KE1xZP100M72SF0RM) 6. Revision history Revision history Revision number Date Substantive changes 12/2016 Initial release KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016 NXP Semiconductors... - Page 23 Information in this document is provided solely to enable system and software How to Reach Us: implementers to use NXP products. There are no express or implied copyright licenses Home Page: granted hereunder to design or fabricate any integrated circuits based on the nxp.com information in this document.
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