NXP Semiconductors KE17Z Series User manual

1 Introduction

Touch Sensing Interface (TSI) provides touch sensing detection on capacitive

touch sensors. The external capacitive touch sensor is typically formed on

PCB. The sensor electrodes are connected to TSI input channels through the

I/O pins in the device.

1.1 KE17Z dual TSI

KE17Z MCU has two TSI modules. It supports two kinds of touch

sensing methods: self-capacitance (also called self-cap) mode and mutual

capacitance (also called mutual-cap) mode.

The dual-TSI technology of KE17Z MCU supports up to 50 touch channels. The

two TSI modules not only increase the number of touch electrode, but also work

in parallel to increase the scanning efficiency of touch electrode and save the

scanning time.

To enhance the liquid tolerance and improve the driving ability, each TSI

module has three shield channels, up to 25 touch channels for self-cap mode,

and up to 6 × 6 touch channels for mutual-cap mode. Both mentioned methods

can be combined on one single PCB, while only the lower 12 TSI channels

TSI[0:11] can be used for mutual mode.

TSI[0:5] are TSI TX pins and TSI[6:11] are TSI RX pins in

mutual mode.

NOTE

• In the self-capacitive mode, developers can use these 50 channels to

design 50 (25 × 2) touch electrodes.

• In the mutual-capacitive mode, design options expand to up to 72 (6 × 6

× 2) touch electrodes.

In some use cases, such as, a multi-burner induction cooker with touch controls

or touch keyboards, the MCUs can support touchscreen designs scaling up

to 98 touch electrodes (26 electrodes using self-capacitance + 72 electrodes

using mutual channels).

1.2 TSI model comparison of KE17Z parts

Table 1 lists the number of TSI channels corresponding to different parts of

KE17Z. These parts all support dual TSI modules.

Contents

1 Introduction......................................1

1.1 KE17Z dual TSI............................1

1.2 TSI model comparison of KE17Z

parts.............................................1

1.3 TSI model comparison between

KE17Z parts and KE15Z parts.....3

1.4 KE17Z dual TSI evaluation board

.....................................................6

2 TSI self-cap mode introduction....... 7

2.1 Self-cap touch sensor.................. 7

2.2 Self-cap sensing mode................ 7

2.3 Clock generation..........................9

2.4 TSI scan time and scan result

accumulation..............................12

2.5 Scan time and sensitivity boost

tests in self-cap mode................15

3 TSI Mutual-cap mode....................18

3.1 Mutual-cap sensor..................... 18

3.2 Clock generation in mutual-cap

mode..........................................19

3.3 Mutual-cap sensing mode..........20

3.4 Sensitivity boost in mutual-cap

mode..........................................23

4 Shield channels.............................24

4.1 Principle of self-cap mode to

improve liquid tolerance by

enabling shield channels........... 24

4.2 Advantages of three shield

channels of KE17Z of each TSI. 25

4.3 Principle of mutual-cap mode to

improve liquid tolerance.............25

5 Hardware design guide................. 25

5.1 Electrode design........................ 26

5.2 PCB trace routing.......................26

5.3 Ground plane............................. 27

5.4 Overlay of the touch electrode...28

5.5 Electrodes placement................ 30

5.6 Hardware checklist.....................30

5.7 X-KE17Z-TSI-EVB touch electrode

patterns design.......................... 30

6 References....................................34

7 Revision history.............................34

Legal information.................................... 35

KE17ZDTSIUG

KE17Z Dual TSI User Guide

Rev. 0 — 05 May 2022 User Guide

Table 1. KE17Z parts supporting dual TSI modules

Product Memory Package IO and ADC channel HMI

Part number Flash

(kB)

SRAM

(kB) Pin count Package GPIOs GPIOs

(INT/HD)

ADC

channels TSI

MKE17Z256VLL7 256 48 100 LQFP 89 89/8 16 50 ch

MKE17Z256VLH7 256 48 64 LQFP 58 58/8 16 47 ch

MKE17Z256VLF7 256 48 48 LQFP 42 42/6 11 31 ch

MKE17Z128VLL7 128 32 100 LQFP 89 89/8 16 50 ch

MKE17Z128VLH7 128 32 64 LQFP 58 58/8 16 47 ch

MKE17Z128VLF7 128 32 48 LQFP 42 42/6 11 31 ch

Table 2. KE17Z dual TSI channels for different package

Product TSI TSI0 TSI1

KE17Z

100LQFP 50 ch 25

channels

TSI0[0: 24]

channels

TSI1[0: 24]

Three shield channels: CH4,

CH12, CH21

Three shield channels: CH4,

CH12, CH21

TX[0:5], RX[6:11] TX[0:5], RX[6:11]

KE17Z

64LQFP

47 ch 22

channels

TSI0[0: 12], [16: 24]

channels

TSI1[0: 24]

No CH13, CH14, CH15

Three shield channels: CH4,

CH12, CH21

Three shield channels: CH4,

CH12, CH21

TX[0:5], RX[6:11] TX[0:5], RX[6:11]

KE17Z

48LQFP

31 ch 15

channels

No CH2, CH3, CH4, CH5, CH13,

CH14, CH15, CH19, CH20,

CH21 16

channels

No CH8, CH9, CH10, CH13,

CH14, CH19, CH20, CH21, CH22

One shield channel: CH12 Two shield channels: CH4, CH12

TX[0:1], RX[6:11] TX[0:5], RX[7,11]

Figure 1 shows the assignment of dual TSI channels on the three packages of KE17Z. Compared with the KE17Z 100LQFP, the

TSI channels marked in yellow are not supported in the KE17Z 64 LQFP. The ones marked in yellow and red are TSI channels

not supported in K17Z 48 LQFP.

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Introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

User Guide 2 / 37

Figure 1. TSI channel assignment of KE17Z 100 LQFP, KE17Z 64 LQFP, and KE17Z 48 LQFP

1.3 TSI model comparison between KE17Z parts and KE15Z parts

Table 3. KE17Z dual TSI channels for different package

Product TSI TSI0 TSI1

KE15Z

100LQFP

MKE15Z256VLL7

MKE15Z128VLL7

25 ch 25

channels

TSI0[0 : 24]

One shield channel: CH12

TX[0:5], RX[6:11]

KE17Z

100LQFP

MKE17Z256VLL7

50 ch 25

channels

TSI0[0: 24]

channels

TSI1[0: 24]

Three shield channels: CH4,

CH12, CH21

Three shield channels: CH4,

CH12, CH21

Table continues on the next page...

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Introduction

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User Guide 3 / 37

Table 3. KE17Z dual TSI channels for different package (continued)

Product TSI TSI0 TSI1

MKE17Z128VLL7 TX[0:5], RX[6:11] TX[0:5], RX[6:11]

KE15Z

64LQFP

MKE15Z256VLH7

MKE15Z128VLH7

25 ch 25

channels

TSI0[0: 24]

One shield channel: CH12

TX[0:5], RX[6:11]

KE17Z

64LQFP

MKE17Z256VLH7

MKE17Z128VLH7

47 ch 22

channels

TSI0[0 : 12], [16 : 24]

channels

TSI1[0:24]

No CH13,CH14,CH15

Three shield channels: CH4,

CH12, CH21

Three shield channels: CH4,

CH12, CH21

TX[0:5], RX[6:11] TX[0:5], RX[6:11]

KE15Z/KE16Z

48LQFP

MKE16Z64VLF4

MKE15Z64VLF4

MKE16Z32VLF4

MKE15Z32VLF4

25 ch 25

channels

TSI0[0: 24]

One shield channel: CH12

TX[0:5], RX[6:11]

KE17Z

48LQFP

MKE17Z256VLF7

MKE17Z128VLF7

47 ch 22

channels

TSI0[0 : 12], [16 : 24]

channels

TSI1[0: 24]

No CH13, CH14, CH15

Three shield channels: CH4,

CH12, CH21

Three shield channels: CH4,

CH12, CH21

TX[0:5], RX[6:11] TX[0:5], RX[6:11]

For the KE17Z in 100LQFP, 64LQFP, and 48LQFP packages, its pin assignment is compatible with the KE15Z. That is, the

number and position of GPIO pins are the same. But the TSI channel assignment of KE17Z is different from KE15Z. To migrate

touch code from KE15Z to KE17Z, see Figure 2, Figure 3, and Figure 4 for the TSI channel assignment. For more migration details,

see

Migration Guide from KE15Z256 to KE17Z256

(document AN13429).

NXP Semiconductors

Introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

User Guide 4 / 37

Figure 2. TSI pin assignment comparison of 100 LQFP between KE15Z and KE17Z

Figure 3. TSI pin assignment comparison of 64 LQFP between KE15Z and KE17Z

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Introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

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Figure 4. TSI pin assignment comparison of 48 LQFP between KE15Z/KE16Z and KE17Z

1.4 KE17Z dual TSI evaluation board

X-KE17Z-TSI-EVB is a touch sensing reference design including multiple touch patterns based on the 5 V Robust KE17Z MCU

of NXP. It has dual-TSI modules and supports up to 50 touch channels, all demonstrated on the board.

Figure 5. X-KE17Z-TSI-EVB, KE17Z dual TSI evaluation board

NXP Semiconductors

Introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

User Guide 6 / 37

2 TSI self-cap mode introduction

The sensor structure and electric field distribution between self-cap sensor and mutual-cap sensor are different.

2.1 Self-cap touch sensor

Ground Hatch

Electrode Ground Hatch

Ground Hatch

PCB

Dielectric Overlay

Cs Cs

ΔCs

via

Routing I/O pin

Self-cap

electrode

Ground hatch

Figure 6. Self-cap touch sensor structure and electric field

In self-cap mode, TSI requires only one pin for each touch sensor. As shown in Figure 6, capacitance exists between electrode

to system ground. Touch changes field through human body and creates extra capacitance.

Self-cap touch sensor structure:

• Cs: Intrinsic self-capacitance. 10 - 50 pF as usual.

• ΔCs: Touch generated self-capacitance. 0.3 - 2 pF as usual.

• Sensitivity of sensor: ΔCs/Cs. 1 - 10 % as usual.

2.2 Self-cap sensing mode

There are three modes of self-cap mode:

• Basic self-cap mode

• Noise cancellation mode

• Sensitivity boost mode

The noise cancellation mode and sensitivity boost mode cannot be enabled at same time. The following describes the

three modes.

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TSI self-cap mode introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

User Guide 7 / 37

2.2.1 Basic self-cap sensing mode

sample

ph 1

Digital SINC

filter

Icx

XIN*Icx

ph 2

Vcx

current mirror: input

TSIx_MODE[S_XIN]

current mirror: charge

TSIx_MODE[S_XCH]

XCH*XIN*Icx

Ci 90pF

Transconductance Amplifier

charge

TSIx_GENC[DVOLT]

Counts

TSIx_DATA[TSICNT]

Vci

IN CHIP

OUT CHIP

I/O

Comparator

Cx = Cs + ΔCs,

Cx is the capacitance of self-cap electrode.

Cs is the self capacitance between touch electrode and ground.

ΔCs is touch generated capacitance.

If no touch happens, Cx = Cs.

TSIx_SINC[CUTOFF]

TSIx_SINC[ORDER]

TSIx_SINC[DECIMATION]

vddlv vdd3v

Figure 7. TSI basic self-cap mode HW architecture

Figure 8. TSI self-cap timing

Inside the TSI IP module, the TSI scan is operated by non-overlapping clock ph1/ph2 and trans-conductance amplifier.

There are two phases controlled by the ph1 and ph2 respectively for the TSI scan module:

• Sample phase: The switch ph1 controls the sample phase. When ph1 turns on, the external touch electrode Cx is charged

by vdd3v.

• Charge phase: The switch ph2 controls the charge phase. When ph1 turns off and then ph2 turns on, the charge on the

capacitor Cx flows to the internal integrated capacitor Ci, which generates the average current Icx.

Via the trans-conductance amplifier, the Icx are amplified to charge Ci and the voltage Vci ramps on Ci. Vci is detected by

comparator, when the Vci becomes larger than the pre-setting Vp, Ci is discharged to negative reference Vm. Then next scanning

cycle continues.

The digital SINC filter controls the scan cycle. The digital SINC filter is a digital decimation filter for filtering out the low frequency

noise from EMC. The digital SINC detects and accumulates the filter number of Vci ramp up steps in per cycle. Digital SINC filter

outputs totally counter which can be read from TSIx_DATA[TSICNT]. The software uses the counts to detect touch.

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TSI self-cap mode introduction

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When touch happens, input capacitance Cx increases. The charging current of Ci becomes larger and then the number of Vci ramp

up steps is reduced. The output count of digital SINC filter is reduced, so the value of TSIx_DATA[TSICNT] is decreased.

2.2.2 Noise cancellation mode of self-cap

If touch sensor encounters strong low frequency noise, noise cancellation can be activated by setting TSIx_MODE[S_NOISE].

In the noise cancellation mode, vdd3v, and vddlv (1.2 V) are dual sample voltages. Two phases exist in noise

cancellation architecture:

• Charging phase of Ci when vdd3v is on and vddlv is off

• Discharging phase of Ci when vdd3v is off and vddlv is on

Two switching clock cycles are cost to samples twice which includes charging phase (sampling vdd3v) and discharging phase

(sampling vddlv). The input current of Ci equal to charging phase current abstract discharging phase current. At the end of each

second phase, low frequency noise is subtracted. In a long integration period, the noise induced error can be canceled.

2.2.3 Sensitivity boost mode of self-cap

The larger parasitic capacitance causes the low sensitivity. The low sensitivity results in the difficulty to recognize the touch event.

For example, when the touch overlay is very thick, it becomes very hard to detect a touch event correctly.

To increase the sensitivity, enable sensitivity-boost feature by removing part parasitic capacitance virtually. So touch works well

under the thicker overlay with sensitivity boost enabled.

The capacitance to be removed cannot be configured more than the intrinsic capacitance of the touch key.

Otherwise, it causes the sensitivity invalid.

NOTE

2.3 Clock generation

The clock generation determines the TSI scan speed. The maximum frequency of TSI is about 10 MHz.

The TSI module is only clocked by the main clock, which is generated by TSI module itself without any other external clock source.

The main clock has four ranges of frequency. It can be divided into the switching clock which is used to control the ph1/ph2

switching speed and finally determines the whole scan time, as shown in Figure 9.

SSC

Main Clock

20.72MHz

16.65MHz

13.87MHz

11.91MHz

SSC_MODE

PRBS SSC

No SSC

Up-down

counter SSC

Touch Key

Switching Clock

SSC_MODE = 10b

SSC_MODE = 00b/01b

basic

advanced

1/ 2

Main Clock

Prescale + 1

Figure 9. Block diagram of clock generation

• When SSC_MODE = 10b, the switching clock is divided from main clock directly, as the basic clock generation.

• When SSC_MODE = 00b/01b, the switching clock is generated from SSC module, as the advanced clock generation.

2.3.1 Basic clock generation

Equation 1 si the basic clock generation, when TSIx_SSC0[SSC_MODE] = 10b.

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TSI self-cap mode introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

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SwitcℎingClock= MainClock

SSC_PRESCALE_NUM + 1  ×  1

Equation 1.

Table 4. Main clock setting

TSI_MODE[SETCLK]

00 20.72

01 16.65

10 13.87

11 11.91

Table 5. Divider setting

TSI_SSC0.SSC_PRESCALE_NUM[7:0]

00000000 divide 1

00000001 divide 2

… …

11111111 divide 256

There is an example of the basic clock generation, the main clock as 16.65 MHz, the divider as 16, and the result of switching clock

is 1.04 MHz.

To use no SSC switching clock with frequency of 1 MHz,

• Set SETCLK < 1:0 > to ‘01b’ to get main clock = 16.65 MHz.

• Set SSC_MODE < 1:0 > to ‘10b’ to disable SSC function.

• Set SSC_PRESCALE_NUM < 7:0 > to ‘00000111b’ to get division 8. When SSC mode is disabled, the frequency is

main

clock/[(SSC_PRESCALE_NUM+1) × 2]

• Keep other registers in TSIx_SSC0, TSIx_SSC1, and TSIx_SSC2 as default value.

SwitcℎingClock=MainClock

Divider  × 1

2=16.65MHz

8 × 1

2 = 1.04MHz

2.3.2 Advanced clock generation, spread spectrum clocking

The Spread Spectrum Clocking (SSC) increases the noise immunity to RF interference and spreads the emissions.

With the SSC enabled (TSIx_SSC0[SSC_MODE] = 00/01b), the switching clock is generated by the SSC module, other than the

direct divided main clock.

In the Self-cap mode, changing the SSC charge time does not affect the final scan result. It changes the total scan time as it

changes the switching clock frequency.

If SSC mode is enabled, the timing of the switching clock generation is as shown in Figure 10.

NXP Semiconductors

TSI self-cap mode introduction

KE17Z Dual TSI User Guide, Rev. 0, 05 May 2022

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