contactless position sensor for variable speed trigger ... · submit documentation feedback ... the...

+

-

BatteryPack +

BatteryPack -

Switch Control

Speed Command

UART/SBW

MicrocontrollerMSP430G2553

3.3 V

20 9�«�42 V

DifferentialElectrodes

+ -

LDOTPS7A16

Voltage SupervisorTPS3839

1TIDUBA0B–December 2015–Revised May 2016Submit Documentation Feedback

Copyright © 2015–2016, Texas Instruments Incorporated

Contactless Position Sensor for Variable Speed Trigger Switch With <65-μAConsumption Reference Design

TI DesignsContactless Position Sensor for Variable Speed TriggerSwitch With <65-μA Consumption Reference Design

All trademarks are the property of their respective owners.

TI DesignsThe TI Design TIDA-00475 demonstrates contactless,robust, cost effective, position sensing for variablespeed trigger switches common in power and gardentools.spaceThe MSP430G2x53 microcontroller accuratelydetermines the trigger position and generates thePWM signal to control motor speed and torque. Thiscapacitive potentiometer enables by design highreliability, long lifetime, and robust operation in harshenvironments. The contactless sensing is inherentlyresistant to damage from moisture or dirt. Therefore, itis an ideal replacement for sensitive, resistivepotentiometers in cost-conscious applications andresolves reliability issues in harsh environments. Thevery low power standby operation of the system avoidsdischarge and damage to the battery pack in case oflong-term storage.

Design Resources

TIDA-00475 Design FolderMSP430G2553 Product FolderTPS3839G33 Product FolderTPS7A16 Product Folder

ASK Our E2E Experts

Design Features• Cost-Efficient Accurate Position Sensing• Robust Operation in Harsh Environment in

Presence of Temperature, Humidity, SupplyVoltages Variations, and ElectromagneticDisturbances

• Step-Less High-Resolution Speed Command• Long Lifetime of Trigger Switch• Low Operation and Standby Current

Featured Applications• Battery-Powered Power Tools• Battery-Powered Garden Tools

An IMPORTANT NOTICE at the end of this TI reference design addresses authorized use, intellectual property matters and otherimportant disclaimers and information.

http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=TIDUBA0B

http://www.ti.com/tool/TIDA-00475

http://www.ti.com/product/MSP430G2553

http://www.ti.com/product/TPS3839G33

http://www.ti.com/product/TPS7A16

http://e2e.ti.com

http://e2e.ti.com/support/applications/ti_designs/

System Description www.ti.com

2 TIDUBA0B–December 2015–Revised May 2016Submit Documentation Feedback



1 System DescriptionState of the art variable speed controls in applications as power and garden tool trigger switches arepredominantly implemented with resistive potentiometers. These consist of a simple slider-based voltagedivider and rely upon a sound electrical contact between resistive coating and sliding wiper contact. Bothcontact and coating are prone to wear down, which inherently limits the lifetime of such potentiometers.Moreover, the common presence of dirt, dust, humidity, and vibration accelerates the degradation of suchpotentiometers, especially in harsh outdoor and construction site environments. Unfortunately, suchcontact-based controls are prone to break down and consequently limit the systems lifetime or requireexpensive repair and replacement.

Contactless sensing technologies as capacitive position sensors do not require any sliding electricalcontacts and are by design durable in harsh environments. The TIDA-00765 demonstrates a reliable,robust, capacitive position sensing solution consisting of a capacitive potentiometer and readout circuitryfor highly cost conscious industrial, consumer, and automotive applications.

The basic position sensing principle of the trigger switch control can be divided into two parts. Firstly,pulling the trigger is converted in the mechanical sensor setup into a capacitance change (see Figure 1).The spring of the trigger bends a tongue protruding out of the printed circuit board (PCB) proportionally tothe triggers position and the force applied. Upon the tongue electrodes are implemented on the top andbottom sides. These are encapsulated on top and bottom by a steady shield attached to the PCB. Whenthe tongue moves, the distance as well as the capacitance between the electrodes and the shield changeaccordingly. Therefore, the sensor capacitance between the shield and electrodes reflects the trigger’sposition.

Figure 1. Mechanical Setup of the System

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www.ti.com System Description




Secondly, the change in capacitances is read out and converted into the trigger speed control command.The top and bottom electrodes are connected to two different pin-oscillators of a MSP430G2553microcontroller. The capacitive sensor alters the oscillation frequencies of the pin oscillators. Theoscillation frequencies for the top and bottom sensor electrodes are successively captured with a timer.The trigger position is derived as the filtered difference of the oscillation frequency counts of the top andbottom electrodes.

This proposed combination of differential capacitive sensing and readout compensates the errorsassociated with changes in temperature, supply voltage, humidity, or large signal influences, as well aslong-term drifts. Moreover, the shielded configuration of the sensor electrodes provides high robustness toelectro-magnetic interference (EMI) required for harsh environments and enables an inexpensivemechanical construction.

The ultra-low-power MSP430G2553 mixed-signal microcontroller outputs the sensed position to the motorcontrol as pulse width modulated (PWM) signal. Unused abundant pin oscillators of the MSP430G2553can digitize additional controls or detect touch or proximity events. The MSP430G2553 can monitor thebattery pack voltage and shut the system off timely in case the battery is drained. The TPS3839 providesabsolutely robust system supervision and reset. The low-drop-out regulator TPS7A16 sub-regulatesbattery pack voltage. Due to the ultra-low power operation, the system is well suited for battery-poweredcordless tools, where the discharge of plugged battery packs must be avoided to ensure battery integrityduring long-term storage of the tools.

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Design Features www.ti.com




2 Design Features

2.1 SpecificationThe specifications of the TIDA-00475 are listed as follows:

Table 1. System Specification of TIDA-00475

SPECIFICATION DESCRIPTION

Functional requirements

Sensing of switch positionSpeed control command output for motor controlMonitoring of battery voltageDrive status LED for optical feedback

Interface to motor control

PWM encoded position signal3.3-V or 5-V logic fault signalUART communicationSpy-Bi-Wire™ for debug

Resolution> 100 steps or < 1% of full scale quantizationNon-linearity < 5% of full scale

Noise immunityIn neutral off position, no false start detection under all test conditionsIn on position < ±5% of full scale peak-to-peak error max

Sampling rate> 10 Sps in standby operation in neutral position> 50 Sps in normal operation

Operation supply voltage 22 to 45 V (minimum 2 V/cell )Currents for system 70-µA average switch in standby operation in neutral positionShutoff mode 5-µA average with VBAT < 18 VOperation temperature –25°C to 85°C

Operation states

(Tool) operation, if reading is above 5% of full scaleStandby, if reading is below 5% of full scaleDebug(Low battery) shutoff

Reliability By design no wear-down of contacts

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Electrode A

Electrode B

h

x

3&%�³7RQJXH´

Grounded Shield

Capacitor generated between electrode A and shield

Capacitor B <->shield

Grounded Shield

r 0 AC

d

e ´ e ´

=

Shield (grounded)

2 electrodes above and EHORZ�WKH�³WRQJXH´�DV�

differential capacitance sensors

3&%�³WRQJXH´

www.ti.com Design Features




2.2 Design TheoryThe system structure of the design is shown in Figure 2.

Figure 2. System Structure

When the user applies force to the "tongue" (the sensor part of the PCB with electrodes) of the board,deformation of the PCB causes a difference of distances on electrodes located on each side of the board.

With Equation 1, the capacitances generated between each electrode and the grounded shield changecorrespondingly to the amount of deformation. The change of capacitance is detected by the pinoscillation feature of the MSP430G2xx family MCU.

(1)

where:• A is the area of the two plates (in meters)• εr is the dielectric constant of the material between the plates• ε0 is the permittivity of free space (8.85 × 10-12 F/m)• d is the separation between the plates (in meters)

Figure 3 shows the capacitance generated between the electrodes and the grounded shield when thePCB tongue is bent.

Figure 3. Capacitors Generated Between Electrodes and Grounded Shield

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pin0sc

TimerA0 Count ValueF

Gate Interval=

CLOAD − External Capacitance − pF

0.00

0.15

0.30

0.45

0.60

0.75

0.90

1.05

1.20

1.35

1.50

10 50 100

P1.y

P2.0 ... P2.5

P2.6, P2.7

VCC = 3.0 V

fosc

−Typic

al O

scill

ation F

requency

−M

Hz

electrode shield r 0

aC dx

d(x)= e e ò

Design Features www.ti.com




The approximate capacitance generated between one electrode and the shield can be calculated usingEquation 2:

(2)

where:• a is the width of the electrode on one side• x is the length of the electrode on one side• d(x) is the distance between the electrode and the shield, which can be taken as d(x) = x tan θ for

approximation (θ is defined by the height of the shield, h in Figure 3, and length of the electrode x)

In this design, a = 9 mm, x = 20 mm, and h = 1.5 mm.

The electrode and the shield generate approximately 0.089 pF when in neutral position, and 0.42 pF(Capacitor B in Figure 3) and 0.055 pF (Capacitor A in Figure 3) when bent to the maximum position intheory. The capacitance generated between the electrodes are not taken into consideration because thiscapacitance is considered to be constant regardless to the position of the tongue and only differentialcapacitance will be processed.

Figure 4 shows the relationship between pin oscillator frequency and the load capacitance on the pin.

Figure 4. Typical Pin Oscillator Frequency of MSP430G2553 With VCC = 3.0 V

Connect the static load capacitance to both pins to ensure that the total load capacitances on the pins arein the device typical characteristic range. In this design, electrode A and electrode B are connected toP2.1 and P2.2. C5 and C6 are applied to each pin with 10-pF capacitors.

Pin oscillation signals are internally routed to timer A0 of the MCU as the INCLK. The firmware usesinternal watchdog timer as the gate interval generator, and later on uses watchdog interrupt serviceroutine to collect the count result. The pin oscillation frequency can be captured and calculated byEquation 3:

(3)

The CLOAD on the corresponding pin can also be determined by checking Figure 4. Therefore, bycomparing the count values by each gate interval, the deformation of the sensor can be detected. ("Count"is used instead of "capacitance" in the latter part of this document.)

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+

-

BatteryPack +

BatteryPack -

Switch Control

Speed Command

UART/SBW

MicrocontrollerMSP430G2553

3.3 V

20 9�«�42 V

DifferentialElectrodes

+ -

LDOTPS7A16

Voltage SupervisorTPS3839

www.ti.com Block Diagram




3 Block DiagramThe TIDA-00475 consists of three main blocks:• The microcontroller MSP430G2553, which performs the capacitive reading of the differential electrodes• The LDO TPS7A16, which provides 3.3 V from the battery pack voltage• The voltage supervisor TPS3839G33, which resets the microcontroller if its supply voltage drops

Figure 5 shows the system block diagram.

Figure 5. System Block Diagram of TIDA-00475

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Clock

System

Brownout

Protection

RST/NMI

DVCC DVSS

MCLK

Watchdog

WDT+

15-Bit

Timer0_A3

3 CC

Registers

16MHz

CPU

incl. 16

Registers

Emulation

2BP

JTAG

Interface

SMCLK

ACLK

MDB

MAB

Port P1

8 I/O

Interrupt

capability

pullup/down

resistors

P1.x

8

P2.x

Port P2

8 I/O

Interrupt

capability

pullup/down

resistors

Spy-Bi-

Wire

Comp_A+

8 Channels

Timer1_A3

3 CC

Registers

XIN XOUT

Port P3

8 I/O

pullup/

pulldown

resistors

P3.x

8 8

RAM

512B

256B

Flash

16KB

8KB

4KB

2KB

USCI A0

UART/

LIN, IrDA,

SPI

USCI B0

SPI, I2C

ADC

10-Bit

8 Ch.

Autoscan

1 ch DMA

Circuit Design and Component Selection www.ti.com




4 Circuit Design and Component Selection

4.1 Microcontroller

4.1.1 Part SelectionThe MSP430G2xx family features several pin oscillators to measure capacitance for highly cost sensitiveapplications and offers superior ultra-low-power operation and standby, which is exploited in this design.

Moreover, the TI MSP430™ family of ultra-low-power MCUs consists of several devices, featuringdifferent sets of peripherals targeted for various applications. The architecture, combined with five low-power modes, is optimized to achieve an extended battery life in portable measurement applications. Thedevice features a powerful 16-bit RISC CPU, 16-bit registers, and constant generators that contribute tomaximum code efficiency.

Wide operation supply-voltage range of 1.8 to 3.6 V and ultra-low power consumption with 230-μA activemode at 1 MHz, 2.2 V, 0.5-μA standby mode, and 0.1-μA off mode features make the MSP430G2553 aperfect fit for battery powered applications including variable speed trigger switch application.

Figure 6. MSP430G2553 Block Diagram

4.1.2 CommunicationTwo communications channels are implemented in the TIDA-00475: Spy-Bi-Wire and UART.

4.1.2.1 Spy-Bi-WireSpy-Bi-Wire communication is used to program the MSP430. A pullup resistor (R17) and capacitor (C7)are usually required on the /RST pin of the MSP430. In the TIDA-00475, R17 is not populated, the pullupfunction being done by the voltage supervisor, as described in Section 4.3.2.

If needed, the RST pin of the jumper J3 may also be used to reset the MSP430.

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www.ti.com Circuit Design and Component Selection




4.1.2.2 UARTA simple UART communication protocol is implemented between the TIDA-00475 and a computer tomonitor the reading performed by the MSP430.

With the communication protocol, the MCU sends out data readings in a data frame of 14 bytes every timewhen a valid data is collected.

The UART data format is set to:• Baud rate: 115200 bps• Parity: None• Data bit: 8 bits• Stop bit: 1 bit

The data frame format of the UART in Build 01 and Build 02 are shown in Table 2:

Table 2. UART Communication Data Frame Definition

BYTE NO NAME DESCRIPTION1 1st digit in ASCII

Build 01: Raw data of electrode ABuild 02: Base count of the system

2 2nd digit in ASCII3 3rd digit in ASCII4 4th digit in ASCII5 5th digit in ASCII6 6th digit in ASCII7 " " in ASCII A space mark8 1st digit in ASCII

Build 01: Raw data of electrode BBuild 02: Filtered data of conversion

9 2nd digit in ASCII10 3rd digit in ASCII11 4th digit in ASCII12 5th digit in ASCII13 6th digit in ASCII14 "\n" in ASCII A new line mark

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42 VR8 R13 1

3 V

æ ö= ´ -ç ÷

è ø





4.1.3 Hardware ImplementationThe first step when designing the MSP430 circuit is the choice of decoupling capacitors. Two X5Rcapacitors, 4.7 μF and 0.1 μF, respectively, were added close to the IC to improve performance.

When choosing the pinout of the MCU, particular attention was given to ensure no fast switching or noisypins are around the sensitive electrodes pins. With the speed command being a PWM, this design usesthe Timer1_A to generate it, so the pinout was also chosen accordingly.

Several signals and functions were used in the pinout and hardware design, but not used in the softwareto allow additional user-added features.

Table 3. Hardware Signal Description

PIN NAME FUNCTION1 DVCC 3.3 V2 SW_FET Signal to control the power switch (not used in the TIDA-00475)3 UCA0RXD TX - UART4 UCA0TXD TX - UART5 Vpack Measure of the battery pack voltage (not used in the TIDA-00475)6 Vpack_RD Control of the battery pack voltage sensing (not used in the TIDA-00475)7 Elect2_A Second pair of electrodes, off board (not used in the TIDA-00475)8 Elect2_B Second pair of electrodes, off board (not used in the TIDA-00475)9 Elect1_A Primary pair of electrodes10 Elect1_B Primary pair of electrodes11 NC —

12 MC_Ready Signal that the motor control circuit is powered, allowing the speed command to be sent (notused in the TIDA-00475)

13 Speed_CMD PWM controlling the motor speed, depending of the trigger position14 NC —15 Fault Fault signal coming from the motor control circuit (not used in the TIDA-00475)16 SBW_RST Reset signal of the Spy-Bi-Wire17 SBW_TEST Test signal of the Spy-Bi-Wire

18 TMP_EN Signal to enable the temperature measurement from the LMT01, off board (not used in theTIDA-00475)

19 TMP_RD Reading of temperature measurement from the LMT01, off board (not used in the TIDA-00475)

20 DVSS Ground

A voltage measurement circuit was added to allow the tracking of the battery voltage of the tool. TwoFETs (Q1 and Q2) were added to control the reading of the voltage, to not have a continuous currentdrawn by the resistor divider.

The resistor divider (R8 and R13) was calculated the following way: R13 was fixed to 10 kΩ. Then R8 iscalculated to give 3 V when the battery pack voltage is 42 V, so

(4)

So R8 is 130 kΩ, which gives us 1.42 V when the battery voltage is 20 V.

Speed command signal together with filter and LED to indicate the position sensed, see Section 4.1.5.2for implementation details.

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9 mm

20 mm

1.5 mm

2 mm 2 mm

2 mm

2 mm

2 mm

2 mm

19 mm

29 mm

A

2 mm2 mm 2 mm

Top

Bottom

FrontBack Left Right (cut along A)

1.5mm





4.1.4 Electrode DesignThe design of the electrodes consist of two parts: the electrodes on the PCB and the shield around.

4.1.4.1 ShieldThis design’s shield is made of plastic, covered in conducting paint, and glued to the board withconductive glue. It could also be made of conducting plastic. The desired shape was obtained thanks to a3D printer. The shield is made out of two parts, one mounted on the top side and one mounted on thebottom side.

Figure 7. Shield Dimensions

4.1.4.2 PCB ElectrodesThe PCB electrodes implemented in this design have the following dimensions:

Figure 8. PCB Electrode Dimension

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Filtered Data BaseCountDuty 100%

Full Scale

-

= ´





4.1.5 Firmware

4.1.5.1 OverviewThe firmware of the TIDA-00475 uses the MSP430G2553 pin oscillation function to detect the amount ofdeformation of the trigger electrodes by sensing the difference of the capacitance loaded to the pins. Thefirmware uses the internal watchdog timer as a gate timer and routes the pin oscillation signals from theelectrodes to Timer A0 of the MSP430 to capture the oscillation of the pins.

For the end user application, the amount of deformation of the trigger electrodes is translated into PWMduty cycle output on the Speed_CMD pin of the system. The user can also monitor the raw data, filtereddata, and base count data detected by the system through UART communication.

4.1.5.2 Build OptionsThere are four different build options provided in the firmware:• Build 01

The firmware provides raw data reading through UART interface. The user may monitor the raw datasteam by connecting a standard UART to COM/USB convert to the PC. In this build option, the systemwill not go to low-power standby mode but continuously sensing the capacitance on the electrodes andsends data out.

• Build 02Similar to Build 01, in this build, the firmware will first detect the base count level of the triggerelectrodes (neutral position) on starting up and the conversion results after the base level detection areprocessed through a simple moving sum filter. The base level count value and the filtered value aresent through UART instead of raw data.

• Build 03In this build option, the firmware monitors the filtered conversion result. If the conversion result showsthat the trigger stays in the neutral position, the system will enter LPM3 mode for approximately 80 msand wakes up to check once whether the trigger is pressed or not.spaceIf the firmware detects the trigger is pressed, it will enter active mode and continuously performs theconversion until the trigger is back to neutral position again for a certain period of time (50 continuoussamples, defined by ACTIVE_TIMEOUT_COUNT).spaceIn this option, the UART communication is disabled to save power.

• Build 04Similar to Build 03, in this build, a PWM output is added to the firmware to indicate the amount ofdeformation of the trigger. The PWM is set to 50 Hz and duty of the PWM is calculated usingEquation 5:

(5)Filtered Data and Base Count are explained in Section 4.1.5.3. Full Scale is the maximum countdifference between filtered data (max. deformation) and the base count (neutral position), which is setto 1500 (defined by TRIGGER_FULL_SCALE) in this design.

4.1.5.3 Frequency HoppingUnlike the regular capacitive touch button application, this design requires accurate continuous reading onpin oscillator counts to determine where exactly the tongue is between the neutral position and themaximum deformation, rather than single threshold comparison.

Since any noise on the VCC (for example, from CPU or other switching activities) could impact the pinoscillation frequency. It is recommended by the Capacitive Touch Library of the MSP430 MCU that theapplication to switch off CPU activities and go to low power modes (for example, LPM0).

To make the application even more robust against potential frequency locking between the operationfrequency and the pin oscillator, DCO frequency hopping method is introduced in this design.

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Filtered Data Offset Sum (electrodeA) Sum (electrodeB)= + -

p p 1 p 2 p nSum (x) x x x x- - -

= + + + +L

t1 t3 t4 t5

Pin Oscillation on electrode A

Pin Oscillation on electrode B

t2 t6





The timing chart in Figure 9 shows the sequence of the DCO frequency hopping during the gate interval.

Figure 9. Timing Sequence of DCO Frequency Hopping

where:• t1: electrode A pin oscillation stabilization time• t2: interval with DCO = 16 MHz• t3: interval with DCO = 15 MHz• t4: interval with DCO = 13 MHz• t5: interval with DCO = 11 MHz• t6: electrode B pin oscillation stabilization time

NOTE: A complete gate interval on a single electrode (such as electrode A) is t1 + t2 + t3 + t4 + t5.

In Build 01 of the firmware, "raw data" is the count on each electrode in a complete gate interval. In Build02, Build 03, and Build 04, the firmware processes the raw data of each electrode by a moving sumalgorithm shown in Equation 6.

(6)

where• n is the total sample points of the filter• xp is the latest sampled value.

In this design, the sample points of the filter are set to 20 (defined by FILTER_SAMPLE_POINTS) bydefault.

The filtered data used by the firmware to determine the position of the electrodes is calculated byEquation 7:

(7)

where:• Offset is 6000 (defined by TRIGGER_FULL_SCALE × FREQ_OPTIONS) in this design to provide a

positive offset to the filtered data.• Sum(electrodeA) and Sum(electrodeB) are the sampled result after filtering

The firmware detects a base count by assuming the tongue is at its neutral position when the system ispowered up. The base count value is the average of the first 100 (defined by BASE_COUNT) reading onthe filtered data after the system is powered.

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Raw Data ± Base Count > WAKEUP_THRESHOLD?

Sleep Mode(LPM3)

- Stop PWM

Single Measurement

[after 80ms]

No

Active Mode(LPM0)

- Continuous Measurement- PWM output

(Filtered Data ± Base Count) lower than ACTIVE_THRESHOLD for longer than

ACTIVE_TIMEOUT_COUNT

Yes

Yes

No





4.1.5.4 Operation ModesIn Build 03 and Build 04 of the firmware, the system enters LPM3 to reduce the total power consumptionof the operation. Figure 10 shows the operation mode switching sequence.

Figure 10. Flowchart of Operation Mode Switching

4.2 Low-Dropout Regulator (LDO)

4.2.1 Part SelectionA DC/DC converter is required to convert the battery voltage to the voltage needed by the microcontroller.In an application with 10 cells in series, the voltage is between 25 and 42 V, with some margin. The TIDA-00475 is designed to work between 20 and 45 V.

Concerning the microcontroller voltage, the MSP430 requires a voltage between 1.8 and 3.6 V.

The current needed in the TIDA-00475 is in the range of couple of μA to couple of mA maximum, butmore importantly, the quiescent current is really critical.

As a power tool is a noisy environment, a good power supply rejection ration (PSRR) also needs to beconsidered when choosing a DC/DC converter.

With all these requirements in mind, the TPS7A1633, 60-Vin, 3.3-VOUT, 5-μA IQ, 100-mA, LDO with Enableand Power Good was chosen.

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4.2.2 Hardware ImplementationThe first step while designing with the TPS7A1633 is to choose the input and output capacitors, here 1 μF(X7R) and 4.7 μF (X5R) where respectively chosen.

One possibility for the enable signal is to connect the EN pin directly to the IN pin. The drawback of thissimple solution is that the LDO will continue working even if the input voltage is a couple of volts; however,in a 10s battery application, this would mean that the battery pack is heavily depleted.

In order to prevent this and to limit the current consumed when the battery is depleted, a small circuitcomposed by a Zener diode (D3), a resistor (R6), and a capacitor (C3) is connected to the enable pin.This way, the LDO is then only enabled if the input voltage is higher than the voltage across D3 plus theenable high level voltage of the LDO (in this case ~19.2 V). D3 can be tuned in case the user wants ahigher or lower enable threshold.

Once the LDO is disabled, only the microcontroller and voltage supervisor are discharging the outputcapacitors of the LDO. As both of these parts are low standby current, this can take some time. Thus, asmall discharge circuit was implemented, with the help of the power good of the LDO. In this case, if theoutput of the LDO drops below ~90% of 3.3 V, then the PG pin is pulled low, allowing D1 and R1 todischarge the output capacitors.

The diodes D2 and D4 could be added to protect respectively against reverse polarity and overvoltage.

4.3 Voltage Supervisor

4.3.1 Part SelectionAs seen previously, the MSP430 requires a voltage between 1.8 and 3.6 V. As the TPS7A16 provides 3.3V, the TPS3839G33, an ultra-low quiescent (150 nA), ultra-small voltage supervisor, monitors the supplyvoltage. It holds the MSP430 in reset in case its supply voltage drops below 3.08 V and the reset outputremains low for 200 ms (typical) after the VDD voltage rises above the threshold voltage and hysteresis.

4.3.2 Hardware ImplementationBecause the MSP430 uses Spy-Bi-Wire communication, a 10-kΩ resistor (R3) is added between theTPS3839G33 and the MSP430 to allow Spy-Bi-Wire communication to occur normally, as well as toensure the /RST pin to be held low if the voltage supervisor detect an undervoltage condition.

4.4 LayoutSee the TPS7A16 and TPS3839G33 datasheets, the Capacitive Touch Hardware Design Guide [1], andSection 7.5 of this report.

4.5 Potential ImprovementIn power tool applications, the temperature can vary over a wide range in a short time, (for example, if thetool is stored in cold environment, then heats up rapidly during operation). To compensate for anytemperature drift, a static capacitor can be applied to a separate pin oscillator to generate a referencemeasurement.

Bending will limit the overall lifetime of the PCB; therefore, in an alternative setup where the electrodes aremoved laterally versus each other will offer superior lifetime of the trigger. Also, this would increase thechange of the sensing capacitances and consequently lead to higher signal-to-noise (SNR) ratio andbetter accuracy.

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Connector to Power Switch SBW connector

Filtered Speed FRPPDQG¶V�FRQQHFWRU�

Connector to Motor control Electodes and Shield

UART Connector

2nd Electrodes pair connector

Pack Voltage measurment

LDOVoltage supervisor

MSP430Power Connector

Getting Started www.ti.com




5 Getting Started

5.1 PCB OverviewFigure 11 shows a picture of the PCB with the function blocks.

Figure 11. TIDA-00475 PCB With Functional Blocks

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www.ti.com Getting Started




5.2 Connectors Settings

Table 4. Connector Settings

CONNECTOR FUNCTIONJ1-1 GNDJ1-2 VIN

J2–1 SpeedFJ2–2 GNDJ3–1 TestJ3–2 GNDJ3–3 /RSTJ4–1 RXJ4–2 GNDJ4–3 TXJ5–1 FaultJ5–2 3.3 VJ5–3 GNDJ5–4 SpeedJ5–5 MC_ReadyJ5–6 Not ConnectedJ6-1 SW_FETJ6-2 TMP_RDJ6-3 GNDJ6-4 TMP_ENJ7-1 EL2AJ7-2 GNDJ7-3 EL2B

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Getting Started www.ti.com




5.3 Build and Program the FirmwareThe TIDA-00475 firmware is provided with four different build options (see Section 4.1.5.2). To changebetween the build options, follow these two steps:1. Right click on the project and select [Build Configurations] → [Set Active] → Select Build options.

Figure 12. 1 Selecting the Active Build

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www.ti.com Getting Started




2. Set Build option with macro BUILD_OPTION in tida-00475.h file. In the file tida-00475.h, from line 43 to63 is the build option setting section. The user may refer to the descriptions on each option and set themacro value at the line 57 to fit the build option selected in Step 1.

Figure 13. Configuring the Code to Fit the Active Build

The user may then build the project and program the firmware into the target board by clicking on the[Debug] button.

In tida-00475.h, these parameters can be modified by the user:• FREQ_OPTIONS: Number of frequencies that is used by frequency hopping mechanism. This

parameter is by default set to 4. This value has to be modified together withDCOCTL_REG_SETTING[] and BCSCTL1_REG_SETTING[] arrays in the main.c. The user may add,remove, or change a frequency setting in the arrays to check the performance of the sampled data.

• FILTER_SAMPLE_POINTS: Number of samples in the moving summation filter. This parameter is bydefault set to 20.

• BASE_COUNT: Number of samples used to generate the base value of the sample. This parameter isby default set to 100.

• ACTIVE_TIMEOUT_COUNT: Number of samples used to judge whether to enter idle mode from activemode. This parameter is set by default to 50.

• TRIGGER_FULL_SCALE: Full scale of the trigger sample value from neutral to maximum bentposition. When frequency options are changed, this value is supposed to be changed accordingly. Thisparameter is by default set to 1500.

• PWM_PERIOD: This value is use to set the PWM period in TA1CCR0 register. It is set by default to40000 with a 20-ms period time at a count clock of 2 MHz.

• WAKEUP_THRESHOLD: Threshold used by wake-up routine to judge whether a sampled data canwake the system up to active mode. When the difference between the latest sampled data and thebase value is greater than this threshold, the system will enter active mode. It is by default set toTRIGGER_FULL_SCALE / 10.

• ACTIVE_THRESHOLD: Threshold used by active routine to judge whether the system can go back toidle mode. When the difference between the sampled data and the base value is less than thisthreshold continuously for ACTIVE_TIMEOUT_COUNT times, the system will enter idle mode. It is setby default to TRIGGER_FULL_SCALE / 20.

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http://www.ti.com/lit/pdf/#TIDUBA08930

Test Data www.ti.com




6 Test Data

6.1 SetupFigure 14 shows the setup and the test equipment used.

Figure 14. Test Setup for TIDA-00475

Table 5. Test Equipment

TEST EQUIPMENT PART NOOscilloscope Tektronix TDS 2024BMultimeter Fluke 87 IIIPower supply Knuerr Heinzinger Polaris 125-5Waveform generator Keysight 33600ATTL-to-USB serial converter TTL-232R-3V3MSP430 programmer MSP430 LaunchPadPower tool 36-V cordless hammer drill

The position of the PCB tongue of the trigger is controlled using a screw of Φ = 2.5 mm, which generatesthread pitch of 0.6 mm each turn. One step of position change in these tests means ¼ of a turn on thescrew (0.15-mm deformation on the tongue).

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Trigger Position

Ave

rage

Cou

nt

0 1 2 3 4 5 6 7 8 9 103000

3200

3400

3600

3800

4000

4200

4400

4600

D001

AVG OffAVG On

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6.2 Test Results

6.2.1 Count versus PositionFor this test, the input of the TIDA-00475 is connected directly with the supply of the 36-V cordlesshammer drill. In this way, the TIDA-00475 sees the same noise, transient, and disturbances as if it wouldbe inside the tool.

The first set of measurements (black curve) is done with the tool not working. The second set ofmeasurements (red curve) is done with the tool turning at full speed in hammer drill mode. Themeasurements are not impacted by the disturbances generated by the tool working.

Figure 15. Counts versus Positions

Standard deviation (STD) and peak-to-peak noise ratio (PP) when the motor of the power tool is on andoff are shown in Table 6:

Table 6. Data Analysis for Linearity Test

POSITIONMOTOR OFF MOTOR ON

AVGOFF

STDON

STD%

PPOFF

PP%

AVGON

STDON

STD%

PPON

PP%

0 3277.8 6.5 0.20 39 1.19 3277.8 7.2 0.22 43 1.311 3278.6 6.9 0.21 43 1.31 3279.4 7.2 0.22 49 1.492 3321.3 6.7 0.20 45 1.35 3316.7 8.6 0.26 60 1.813 3427.7 8.5 0.25 52 1.52 3429.5 7.0 0.20 40 1.174 3572.8 7.3 0.20 45 1.26 3574.6 7.7 0.21 47 1.315 3722.3 8.3 0.22 48 1.29 3720.6 7.1 0.19 40 1.086 3867.3 11.8 0.30 87 2.25 3869.6 8.2 0.21 71 1.837 4003.5 9.4 0.23 56 1.40 4036.7 6.6 0.16 39 0.978 4177.7 7.2 0.17 44 1.05 4204.4 7.8 0.19 54 1.289 4328.9 8.9 0.21 59 1.36 4367.3 7.6 0.18 45 1.03

6.2.2 AC Noise Injection TestTo test the effect of the power supply noise on the MSP430 measurements, the following test wasperformed: The TIDA-00475 board is supplied by a lab supply at 36 V, in series with a waveformgenerator. The waveform generator is then adding noise on the 36-V supply.

The noise injected varies from 2 mVPP, 5 VPP, 10 VPP, and 20 VPP, and the bandwidth of the noise injectedis either 1 kHz, 20 kHz, or 100 kHz.

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AC Noise Bandwidth (kHz)

Pea

k-P

eak

Noi

se (

in c

ount

)

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

100

D004

2 mV5 V10 V15 V20 V


Ave

rage

Cou

nt

0 20 40 60 80 100 1203200

3220

3240

3260

3280

3300

3320

3340

3360

3380

3400

D002

2 mV5 V10 V15 V10 V


Sta

ndar

d D

evia

tion

(in c

ount

)

0 20 40 60 80 100 120-1

1

3

5

7

9

11

13

15

D003

2 mV5 V10 V15 V20 V





6.2.2.1 Test Results In Neutral Position

Figure 16. Average Counts versus Noise Amplitude inNeural Position

Figure 17. Standard Deviation versus Noise Amplitude inNeural Position

Figure 18. Peak-to-Peak Noise versus Noise Amplitude in Neural Position

Table 7. Test Data in Count According to Injected Noise in Neural Position

NOISE POSITION 0, TOOL OFFVPP (V) BANDWIDTH (kHz) AVG OFF STD OFF PP STD % PP %

2 mV1 3305.01 7.70 49 0.23 1.48

20 3304.59 7.13 38 0.22 1.15100 3310.09 6.86 42 0.21 1.27

51 3307.17 7.78 40 0.24 1.21

20 3304.35 6.90 47 0.21 1.42100 3311.84 7.96 54 0.24 1.63

101 3303.51 7.44 47 0.23 1.42

20 3306.66 6.85 39 0.21 1.18100 3311.25 7.35 41 0.22 1.24

151 3305.15 8.00 50 0.24 1.51

20 3302.95 7.25 54 0.22 1.63100 3309.09 7.75 53 0.23 1.60

201 3310.25 9.21 62 0.28 1.87

20 3309.10 7.15 44 0.22 1.33100 3305.69 8.72 48 0.26 1.45

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Pea

k-P

eak

Noi

se (

in c

ount

)

0 20 40 60 80 100 1200

10

20

30

40

50

60

70

80

90

100

D007

2 mV5 V10 V15 V10 V


Ave

rage

Cou

nt

0 20 40 60 80 100 1203200

3400

3600

3800

4000

4200

4400

4600

4800

5000

D005

2 mV5 V10 V15 V10 V


Sta

ndar

d D

evia

tion

(in c

ount

)

0 20 40 60 80 100 120-1

1

3

5

7

9

11

13

15

D006

2 mV5 V10 V15 V10 V





6.2.2.2 Test Results In Maximum Position

Figure 19. Average Counts versus Noise Amplitude inMaximum Position

Figure 20. Standard Deviation versus Noise Amplitude inMaximum Position

Figure 21. Peak-to-Peak Noise versus Noise Amplitude in Maximum Position

Table 8. Test Data in Count According to Injected Noise in Maximum Position

NOISE POSITION FS, TOOL OFFVPP (V) BANDWIDTH (kHz) AVG OFF STD OFF PP STD % PP %

2 mV1 4268.90 9.10 49 0.21 1.15

20 4268.47 7.95 47 0.19 1.10100 4264.03 9.19 50 0.22 1.17

51 4271.50 8.09 50 0.19 1.17

20 4269.39 8.68 61 0.20 1.43100 4265.80 8.14 48 0.19 1.13

101 4264.60 7.76 42 0.18 0.98

20 4267.60 6.83 43 0.16 1.01100 4267.73 8.77 53 0.21 1.24

151 4263.02 7.45 47 0.17 1.10

20 4265.34 10.35 55 0.24 1.29100 4267.86 7.48 46 0.18 1.08

201 4262.83 7.89 52 0.18 1.22

20 4272.67 7.69 48 0.18 1.12100 4270.52 7.52 43 0.18 1.01

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In Figure 22, Figure 23, and Figure 24, the pink curve is the noise signal generated by the signalgenerated, which is later added on to the DC power supply of TIDA-00475 board. In the following figures,the signals are AC coupled.

Figure 22. Input of TPS7A16 With 1-kHz BandwidthNoise

Figure 23. Input of TPS7A16 With 20-kHz BandwidthNoise

Figure 24. Input of TPS7A16 With 100-kHz Bandwidth Noise

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6.2.3 DC Power Supply Voltage Test

6.2.3.1 Power Supply Startup and ShutdownThese measurements are performed with the 36-V cordless hammer drill powering the TIDA-00475 boardand plugging in and out the battery pack.

During startup, the /RST pin is asserted high 200 ms after the 3.3-V rail ramped up.

Figure 25. Startup

During shutdown, the /RST pin is pulled low when the 3.3-V rail drops, preventing the MSP430 to workwith a not appropriate voltage.

Figure 26. Shutdown Figure 27. Shutdown (Zoomed in)

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( )867 A 6.8 ms 9.4 A 99 msAverage Current Consumption 64.5 A

105.8 ms

m ´ + m ´= = m

Input Voltage (V)

Inpu

t Cur

rent

(µ

A)

0 5 10 15 200

0.2

0.4

0.6

0.8

1

1.2

1.4

D008





6.2.4 Standby PowerFigure 28 is showing the current consumed when the input voltage is below 17 V, ensuring that the LDO isnot enable. Those measurements were done with a lab supply providing the power and a multimetermeasuring the current.

D4 was not populated and D2 is here replaced by a 0-Ω resistor.

Figure 28. Standby Current When VIN < 17 V

When testing for current consumption in operation, the TIDA-00475 board is powered by 36-V DC powersupply. A 3-kΩ resistor is placed in position of R4 and the voltage across R4 is measured by oscilloscopeto show the current consumption of the system in normal operation (firmware Build 03) with the PCBtongue in neutral position.

Figure 29. Voltage Across R4 When VIN = 36 V

Active mode of the system takes 6.8 ms in every 105.8-ms wakeup period and consumes about 867-µA(2.6-V/3-kΩ) current. When system goes to idle mode, the current consumption is measured by a digitalmultimeter that is connected in series to the power supply and reads 9.4 µA.

The overall average system current consumption is calculated to be:

(8)

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DC Supply Voltage (V)

Pea

k-P

eak

Noi

se (

in c

ount

)

15 20 25 30 35 40 450

10

20

30

40

50

60

70

80

90

100

D011

Position 0Position FS

DC Supply Voltage (V)

Ave

rage

Cou

nt

15 20 25 30 35 40 450

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

D009


DC Supply Voltage (V)S

tand

ard

Dev

iatio

n (in

cou

nt)

15 20 25 30 35 40 450

2

4

6

8

10

12

14

D010






6.2.5 Influence of Power Supply VariationTo measure the influence of the power supply variation, the TIDA-00475 was powered with the lab supply,fixed positions was applied (neutral position and full scale position), and measurements were performed atdifferent supply voltages (typ. 20 V, 24 V, 30 V, 36 V, and 42 V).

System performance is shown in the following figures and table:

Figure 30. Average Counts versus Different DC PowerSupplies

Figure 31. Standard Deviation versus Different DCPower Supplies

Figure 32. Peak-to-Peak Noise versus Different DC Power Supplies

Table 9. Test Data in Count According to Different DC Supply Voltages

POSITION DC SUPPLY (V)TOOL OFF

AVG OFF STD OFF PP STD % PP %

Position 0

21 3329.85 6.94 43 0.21 1.2924 3332.56 7.87 50 0.24 1.5030 3331.56 8.43 46 0.25 1.3836 3331.21 8.70 52 0.26 1.5642 3336.43 7.06 43 0.21 1.29

Position FS

21 4284.75 9.15 52 0.21 1.2124 4282.38 7.59 55 0.18 1.2830 4269.29 6.56 45 0.15 1.0536 4267.71 7.62 53 0.18 1.2442 4271.15 8.99 64 0.21 1.50

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Gate Intervals (Each Gate Interval = 6.8 ms)

Avera

ge C

oun

t

1107

213

319

425

531

637

743

849

955

1061

1167

1273

1379

1485

1591

1697

1803

1909

2015

2121

2227

2333

2439

2545

2651

2757

2863

2969

3075

3181

3287

3393

3499

3605

3711

3817

3923

4029

4135

4241

4347

4453

4559

4665

4771

4877

4983

5089

5195

5301

5407

5513

5619

5725

5831

5937

6043

6149

8200

8250

8300

8350

8400

8450

8500

8550

8600

8650

8700

D012

Phase 2Touch on shield = yes

Phase 1Touch on shield = no

Phase 3Touch on shield = no





6.2.6 Touch ShieldTouch on the shield or ground signals does not affect the measurement result of the design. To show theperformance of the system when touch happens to the shield (ground), data is captured for a period oftime (approximately 1 minute) during which a touch event happens to the shield.

Figure 33 shows the data measured on the trigger when it stays in neutral position during this test periodof time.

Figure 33. Measured Data During Touch-on-Shield

For each phase, the average count, standard deviation, and peak-to-peak noise are shown in Table 10:

Table 10. Data Analysis for Touch-on-Shield Event

PHASE TOUCH AVERAGE STDEV PP1 No 8624.103 6.545 332 Yes 8626.188 8.775 523 No 8627.114 7.678 42

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OUT1

DNC2

PG3

4

EN5

NC6

DELAY7

IN8

9

EP GND

U2

TPS7A1633DGNR

DVCC1

P1.0/TA0CLK/ACLK/A0/CA02

P1.1/TA0.0/UCA0RXD/UCA0SOMI/A1/CA13

P1.2/TA0.1/UCA0TXD/UCA0SIMO/A2/CA24

P1.3/ADC10CLK/A3/VREF-/VEREF-/CA3/CAOUT5

P1.4/SMCLK/UCB0STE/UCA0CLK/A4/VREF+/VEREF+/CA4/TCK6

P1.5/TA0.0/UCB0CLK/UCA0STE/A5/CA5/TMS7

P2.0/TA1.08

P2.1/TA1.19

P2.2/TA1.110

P2.3/TA1.011

P2.4/TA1.212

P2.5/TA1.213

P1.6/TA0.1/A6/CA6/UCB0SOMI/UCB0SCL/TDI/TCLK14

P1.7/A7/CA7/CAOUT/UCB0SIMO/UCB0SDA/TDO/TDI15

RST/NMI/SBWTDIO16

TEST/SBWTCK17

P2.7/XOUT18

P2.6/XIN/TA0.119

DVSS20

U3

MSP430G2553IPW20

GND

Vpack

GND

1

23

Q22N7002ET1G

3

1

2

Q1TP0610K-T1-GE3

Vbat

1

2

J1

OSTTC022162

V3_3

GND

SBW_TESTSBW_RST

UCA0RXD

UCA0TXD

V3_3

V3_3

GND

1µFC1

GND

Elect1_A

Elect1_B

Speed_CMD

MC_Ready

Fault TMP_EN

TMP_RD

SW_FET

Vpack

Vbat

18V

D3MMSZ5248B-7-F

GND1

RESET2

VDD3

U1

TPS3839G33DBZR

V3_3

GND

SBW_RST

Vpack_RD

Vpack_RD

GND

Elect2_A

Elect2_B

Red

21

D1

D2

MBRA160T3G

75V

D4SMCJ75A

Green

21

D8

4

1

2

3

J6

61300411121

1

2

J2

61300211121

UCA0RXD

UCA0TXD

E5E4

GND

GND

GND

E3E2

GND

GND

GND

V3_3

GND

Speed_CMD

MC_Ready

Fault

GNDTMP_EN

TMP_RD

SW_FET

GND

Speed_CMD10k

R9

RC to update

SBW_RST

SBW_TEST

E7 E9

GND

GND

E8

E1

GND

GND

GNDGND

3.9V

D5DNP

3.9V

D13DNP

3.9V

D16DNP

3.9V

D14DNP

3.9V

D9DNP

3.9V

D10DNP

E11 E12

GND

GND

E103.9V

D17DNP

3.9V

D18DNP

3.9V

D19DNP

3.9V

D11DNP

3.9V

D12DNP

2200pFC4

E6

3.9V

D15DNP

GND

Elect2_A

Elect2_BGND

E13

GND

GND

3.9V

D20DNP

3.9V

D21DNP

10k

R3

100

R14

100

R16

3.9V

D6DNP

3.9V

D7DNP

GND

100

R10

100

R11

100

R23

100

R33

100

R32

100

R22

100

R21

100

R31

100

R30

100

R20

100

R39

100

R45

100

R44

100

R38

100

R37

100

R41

100

R43

100

R42 100

R40 100

R36

100

R35 100

R28100

R25

100

R26

100

R27

100

R24

100

R29

100

R34

100

R41.0kR1

1.0kR19

10MR6

10kR17

DNP

10.0kR13

100kR5

100kR7

100kR15

130kR8

4.7µFC2

4.7µFC8

0.1µFC9

1000pFC3

2200pFC7

1

2

3

J3

61300311121

1

2

3

J4

61300311121

1

2

3

J7

61300311121

E14

0R12

0

R2

10.0kR18

GND

10pFC6 10pF

C5

1 2

3 4

5 6

J5

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7 Design Files

7.1 SchematicsTo download the schematics, see the design files at TIDA-00475.

Figure 34. TIDA-00475 Schematics

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Design Files www.ti.com




7.2 Bill of MaterialsTo download the bill of materials (BOM), see the design files at TIDA-00475.

Table 11. BOM

ITEM QTY REFERENCE VALUE PART DESCRIPTION MANUFACTURER MANUFACTURERPARTNUMBER PCB FOOTPRINT

1 1 !PCB1 Printed Circuit Board Any TIDA-00475

2 1 C1 1uF CAP, CERM, 1 µF, 100 V, +/- 10%, X7R,1206 MuRata GRM31CR72A105KA01L 1206

3 2 C2, C8 4.7uF CAP, CERM, 4.7 µF, 6.3 V, +/- 20%, X5R,0402 Wurth Elektronik 885012105008 0402

4 1 C3 1000pF CAP, CERM, 1000 pF, 50 V, +/- 10%, X7R,0402 Wurth Elektronik 885012205061 0402

5 2 C4, C7 2200pF CAP, CERM, 2200 pF, 10 V, +/- 10%, X7R,0402 Wurth Elektronik 885012205008 0402

6 2 C5, C6 10pF CAP, CERM, 10 pF, 50 V, +/- 5%,C0G/NP0, 0402 MuRata GRM1555C1H100JA01D 0402

7 1 C9 0.1uF CAP, CERM, 0.1 µF, 6.3 V, +/- 20%, X5R,0402 Wurth Elektronik 885012105001 0402

8 1 D1 Red LED, Red, SMD Wurth Elektronik 150060RS75000 LED_06039 1 D2 60V Diode, Schottky, 60V, 1A, SMA ON Semiconductor MBRA160T3G SMA10 1 D3 18V Diode, Zener, 18 V, 500 mW, SOD-123 Diodes Inc. MMSZ5248B-7-F SOD-12311 1 D4 75V Diode, TVS, Uni, 75V, 1500W, SMC Fairchild Semiconductor SMCJ75A SMC12 1 D8 Green LED, Green, SMD Wurth Elektronik 150060GS75000 LED_0603

13 3 H1, H2, H3 Machine Screw, Round, #4-40 x 1/4, Nylon,Philips panhead B&F Fastener Supply NY PMS 440 0025 PH Screw

14 3 H4, H5, H6 Standoff, Hex, 0.5"L #4-40 Nylon Keystone 1902C Standoff

15 1 J1 Terminal Block, 2-pole, 200mil, TH On-Shore Technology OSTTC022162THD, 2-Leads, Body10.16x7.6mm, Pitch

5.08mm

16 1 J2 Header, 2.54 mm, 2x1, Gold, TH Wurth Elektronik 61300211121 Header, 2.54mm,2x1, TH

17 3 J3, J4, J7 Header, 2.54 mm, 3x1, Gold, TH Wurth Elektronik 61300311121 Header, 2.54mm,3x1, TH

18 1 J5 Header, 2.54mm, 3x2, Gold, TH Wurth Elektronik 61300621121 Header, 2.54mm,3x2, TH

19 1 J6 Header, 2.54 mm, 4x1, Gold, TH Wurth Elektronik 61300411121 Header, 2.54mm,4x1, TH

20 1 Q1 -60V MOSFET, P-CH, -60 V, -0.185 A, SOT-23 Vishay-Siliconix TP0610K-T1-GE3 SOT-2321 1 Q2 60V MOSFET, N-CH, 60 V, 0.26 A, SOT-23 ON Semiconductor 2N7002ET1G SOT-23

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Table 11. BOM (continued)

ITEM QTY REFERENCE VALUE PART DESCRIPTION MANUFACTURER MANUFACTURERPARTNUMBER PCB FOOTPRINT

22 2 R1, R19 1.0k RES, 1.0 k, 5%, 0.063 W, 0402 Vishay-Dale CRCW04021K00JNED 040223 2 R2, R12 0 RES, 0, 5%, 0.063 W, 0402 Vishay-Dale CRCW04020000Z0ED 040224 1 R3 10k RES, 10 k, 5%, 0.063 W, 0402 Vishay-Dale CRCW040210K0JNED 0402

25 31

R4, R10, R11, R14, R16,R20, R21, R22, R23,R24, R25, R26, R27,R28, R29, R30, R31,R32, R33, R34, R35,R36, R37, R38, R39,R40, R41, R42, R43,R44, R45

100 RES, 100, 5%, 0.063 W, 0402 Vishay-Dale CRCW0402100RJNED 0402

26 3 R5, R7, R15 100k RES, 100 k, 5%, 0.063 W, 0402 Vishay-Dale CRCW0402100KJNED 040227 1 R6 10Meg RES, 10 M, 5%, 0.063 W, 0402 Vishay-Dale CRCW040210M0JNED 040228 1 R8 130k RES, 130 k, 1%, 0.063 W, 0402 Vishay-Dale CRCW0402130KFKED 040229 1 R9 10k RES, 10 k, 5%, 0.1 W, 0603 Vishay-Dale CRCW060310K0JNEA 060330 2 R13, R18 10.0k RES, 10.0 k, 1%, 0.063 W, 0402 Vishay-Dale CRCW040210K0FKED 0402

31 1 U1 Ultralow Power, Supply Voltage Supervisor,DBZ0003A Texas Instruments TPS3839G33DBZR DBZ0003A

32 1 U2

Single Output LDO, 100 mA, Fixed 3.3 VOutput, 3 to 60 V Input, with Enable andPower Good, 8-pin MSOP (DGN), -40 to125 degC, Green (RoHS & no Sb/Br)

Texas Instruments TPS7A1633DGNR DGN0008C

33 1 U3

16 MHz Mixed Signal Microcontroller with16 KB Flash, 512 B SRAM and 24 GPIOs, -40 to 85 degC, 20-pin SOP (PW), Green(RoHS & no Sb/Br)

Texas Instruments MSP430G2553IPW20 PW0020A

34 0

D5, D6, D7, D9, D10,D11, D12, D13, D14,D15, D16, D17, D18,D19, D20, D21

3.9V Diode, Zener, 3.9 V, 200 mW, SOD-323 Diodes Inc. MMSZ5228BS-7-F SOD-323

35 0 FID1, FID2, FID3 Fiducial mark. There is nothing to buy ormount. N/A N/A Fiducial

36 0 R17 10k RES, 10 k, 5%, 0.063 W, 0402 Vishay-Dale CRCW040210K0JNED 0402

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7.3 PCB Layer PlotsTo download the PCB layer plots, see the design files at TIDA-00475.

Figure 35. Top Overlay Figure 36. Top Solder Mask

Figure 37. Top Layer Figure 38. Bottom Layer

Figure 39. Bottom Solder Mask Figure 40. Bottom Overlay

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Socket added for ESD diode protection, but not populated

Decoupling capacitors, placed as close as possible

to the device

Areas free of noisy signals

100-��UHVLVWRUV�SODFHG�DV�close as possible to the Pins





Figure 41. Drill Drawing Figure 42. Board Dimensions

7.4 Altium ProjectTo download the Altium project files, see the design files at TIDA-00475.

7.5 Layout GuidelinesDevice specific layout guidelines for each individual TI part used in this design can be found in theircorresponding datasheet. The following figures provide layout guidelines specific to the TIDA-00475design.

Because of the tradeoff between size, cost, and complexity of the layout, a two-layer board with allcomponents on the top side was chosen.

Particular attention was given to the routing of the electrodes from the MSP430 to avoid high switchingsignals coming close or under the traces or the electrodes themselves. As mentioned in Section 4.1.3, thepinout was chosen to achieve the same goal.

Figure 43. MSP430 Layout

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Input Capacitor (X7R) placed close to the LDO

Output Capacitor (X5R) placed close to the LDO





Figure 44. TPS7A16 Layout

Some spark gaps (E1 through E16) were added on the connectors that are going out of board (UART,Spy-Bi-Wire, connection to other boards, or second pair of electrodes) to help the board withstandpotential ESD event. In a final application, those ESD protections may not be all needed. With the samegoal in mind, the sockets to add protection diodes on the same connectors were designed in but thediodes not populated.

7.6 Gerber FilesTo download the Gerber files, see the design files at TIDA-00475.

7.7 Assembly DrawingsTo download the assembly drawings, see the design files at TIDA-00475.

Figure 45. Top Assembly Drawing Figure 46. Bottom Assembly Drawing

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www.ti.com References




8 References

1. Texas Instruments, Capacitive Touch Hardware Design Guide, MSP430 Design Guide (SLAA576)

9 About the AuthorsDr. BJOERN OLIVER EVERSMANN is a system architect in the Industrial Systems team at TexasInstruments, who is responsible for defining and implementing TI Designs for industrial applications.

KEVIN STAUDER is a system engineer in the Industrial Systems team at Texas Instruments, who isresponsible for developing TI Designs for industrial applications.

RENTON MA is a system engineer in the Industrial Systems team at Texas Instruments, who isresponsible for developing TI Designs for industrial applications.

The authors would like to give special recognition to the contribution from JOHANN ZIPPERER for initialconcept proposal and helpful support, and from LEO HENDRAWAN for his helpful support.

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http://www.ti.com/lit/pdf/SLAA576

Revision B History www.ti.com



Revision History

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