TouchXpress™ Family
CPT213B Data Sheet
The CPT213B device, part of the TouchXpress family, is designed
to quickly add IEC 60730 Class B capacitive touch via an I2C in-
terface by eliminating the firmware complexity and reducing the
development time for capacitive sensing applications.
Supporting up to 13 capacitive sensor inputs in packages as small as a 4 mm x 4 mm
QFN, the CPT213B is a highly-integrated device that interfaces via I2C to the host pro-
cessor to provide a simple solution for adding capacitive touch. The device also comes
with advanced features like an IEC safety library and moisture immunity. No firmware de-
velopment is needed, and all the capacitive touch sense parameters can be configured
using a simple GUI-based configurator. By eliminating the need for complex firmware de-
velopment, the CPT213B device enables rapid user interface designs with minimal de-
velopment effort.
The CPT213B device is ideal for a wide range of capacitive touch applications including
the following:
KEY FEATURES
• No firmware development required
• Simple GUI-based configurator
• 13 Capacitive Sensor inputs with
programmable sensitivity
• IEC-compliant I2C interface to
communicate to and configure from the
host
• IEC 60730 Class B safety library
• Superior noise immunity: SNR up to 270:1
• Moisture immunity
• Home appliances
• White goods
• Instrument / Control panels
• Medical equipment
• Lighting control
Input
Features
Output
Features
Capacitive Touch Sensing
Features
Baselining
IEC Safety
Library
Input Engine
with
13 Inputs
Lowest power mode with feature operational:
Active
IEC-Compliant
I2C Output I2C Event Buffer
Interrupt Pin
Configuration
Profile for each
Input
Touch
Qualification
silabs.com | Building a more connected world. Rev. 1.1
1. Feature List and Ordering Information
R
Tape and Reel (Optional)
G M
Temperature Grade — –40 to +85 °C (G)
13
T–2 B A –
Package Type — QFN24 (M)
01
CP
Silicon Labs Xpress Product Line
Firmware Revision
Hardware Revision
Interface Type — GPO (0), I2C (1), Configuration I2C (2)
Number of Capacitive Sense Inputs
TouchXpress Family
Capacitive Sense Features — Button (B)
Figure 1.1. CPT213B Part Numbering
The CPT213B has the following features:
• Capacitive sensing input engine with 13 inputs
• Post-sample touch qualification engine
• IEC safety library
• Configuration profile space in non-volatile memory
• IEC-compliant I2C event buffer with interrupt pin to signal when new touch events have been qualified
• Configuration loading with both the dedicated configuration interface and through the I2C interface
Table 1.1. Product Selection Guide
Ordering
Part Number
Configuration over I2C
Pb-free
(RoHS Compliant)
Temperature Range
Package
CPT213B-A01-GM Yes Yes -40 to +85 °C QFN24
See http://www.silabs.com/products/interface/capacitive-touch-controllers for other devices available in the TouchXpress family.
CPT213B Data Sheet
Feature List and Ordering Information
silabs.com | Building a more connected world. Rev. 1.1 | 2
Table of Contents
1. Feature List and Ordering Information ......................2
2. Typical Connection Diagrams .........................5
2.1 Signal, Analog, and Power Connections .....................5
2.2 Configuration ..............................6
3. Electrical Specifications ...........................7
3.1 Electrical Characteristics ..........................7
3.1.1 Recommended Operating Conditions ....................7
3.1.2 Power Consumption..........................7
3.1.3 Reset and Supply Monitor ........................8
3.1.4 Configuration Memory .........................8
3.1.5 I2C Configuration Interface .......................9
3.1.6 Capacitive Sense...........................10
3.1.7 IEC 60730 Safety Timing ........................11
3.2 Thermal Conditions ............................11
3.3 Absolute Maximum Ratings .........................12
3.4 Typical Performance Curves .........................13
4. Functional Description ........................... 15
4.1 Capacitive Sensing Input ..........................15
4.1.1 Introduction ............................15
4.1.2 Touch Qualification Criteria .......................15
4.1.3 Thresholds .............................15
4.1.4 Debounce Counter ..........................16
4.1.5 Touch Deltas ............................16
4.1.6 Auto-Accumulation and Averaging .....................16
4.1.7 Drive Strength............................16
4.1.8 Active Mode Scan Enable ........................16
4.1.9 Active Mode Scanning .........................16
4.1.10 No Confidence Mode .........................16
4.1.11 IEC60730 Functionality ........................17
4.2 I2C Event Buffer Interface ..........................17
4.2.1 Introduction ............................17
4.2.2 Startup Behavior ...........................17
4.2.3 Sensing Mode Event Packet Structure ...................18
4.2.4 CRC Algorithm ...........................20
4.2.5 Packet Retrieval in Sensing Mode .....................21
4.2.6 Defined Event Types .........................21
4.2.7 Description Bytes for Touch Events ....................22
4.2.8 Description Bytes for Status Events ....................22
4.2.9 Slave Address............................22
4.2.10 Entering Sensing Mode from Configuration Loading Mode ............23
4.2.11 Determining Configuration Validity ....................23
4.2.12 Configuration Loading Procedure .....................24
silabs.com | Building a more connected world. Rev. 1.1 | 3
4.3 Configuration Profile............................24
5. Pin Definitions ..............................25
5.1 CPT213B QFN24 Pin Definitions .......................25
6. QFN24 Package Specifications........................ 27
6.1 QFN24 Package Dimensions.........................27
6.2 PCB Land Pattern ............................29
6.3 Package Marking .............................30
7. Relevant Application Notes .........................31
8. Revision History .............................32
8.1 Revision 1.1 ..............................32
8.2 Revision 1.0 ..............................32
silabs.com | Building a more connected world. Rev. 1.1 | 4
2. Typical Connection Diagrams
2.1 Signal, Analog, and Power Connections
Figure 2.1 Connection Diagram on page 5 shows a typical connection diagram for the power pins of CPT213B devices.
CPT213B
Device
4.7 µF and 0.1 µF bypass
capacitors required for the power
pins placed as close to the pins as
possible.
1.8-3.6 V (in)
Host
Processor
1.8-3.6 V (in)
...
1.8-3.6 V (in)
Electrode
Electrode
GND
VDD
EB_SCL
EB_INT
CS12
CS00
Config Data
Config Clk / RSTb
EB_SDA
1 kΩ
1-10 kΩ 1-10 kΩ
Figure 2.1. Connection Diagram
Note: The I2C pull-up resistor values will vary depending on the speed requirements of the bus and the host processor requirements.
CPT213B Data Sheet
Typical Connection Diagrams
silabs.com | Building a more connected world. Rev. 1.1 | 5
2.2 Configuration
There are two ways to configure the CPT213B: through the I2C interface, and through the dedicated configuration interface. The dia-
gram below shows a typical connection diagram for the dedicated configuration interface pins. The ToolStick Base Adapter is available
on the evaluation board.
Note: The USB Debug Adapter does not support configuration for TouchXpress devices. Instead, the ToolStick Base Adapter must be
used to configure these devices.
CPT213B Device
Config Clk
1 k
VDD
Config Data
GND
ToolStick
Figure 2.2. Configuration Connection Diagram
CPT213B Data Sheet
Typical Connection Diagrams
silabs.com | Building a more connected world. Rev. 1.1 | 6
3. Electrical Specifications
3.1 Electrical Characteristics
All electrical parameters in all tables are specified under the conditions listed in 3.1.1 Recommended Operating Conditions, unless sta-
ted otherwise.
3.1.1 Recommended Operating Conditions
Table 3.1. Recommended Operating Conditions
Parameter Symbol Test Condition Min Typ Max Unit
Operating Supply Voltage on VDD VDD 1.8 2.4 3.6 V
Minimum RAM Data Retention
Voltage on VDD1
VRAM — 1.4 — V
Operating Ambient Temperature TA–40 — 85 °C
Note:
1. All voltages with respect to GND.
3.1.2 Power Consumption
See 3.4 Typical Performance Curves for power consumption plots.
Table 3.2. Power Consumption
Parameter Symbol Test Condition Min Typ Max Unit
Active Mode Supply Current IDD Sensing Mode — 3.6 — mA
Configuration Mode — 3.6 — mA
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 7
3.1.3 Reset and Supply Monitor
Table 3.3. Reset and Supply Monitor
Parameter Symbol Test Condition Min Typ Max Unit
VDD Supply Monitor Threshold VVDDM Reset Trigger 1.7 1.75 1.8 V
VWARN Early Warning 1.8 1.85 1.9 V
Power-On Reset (POR) Monitor
Threshold
VPOR Rising Voltage on VDD — 1.75 — V
Falling Voltage on VDD 0.75 1.0 1.3 V
VDD Ramp Time tRMP Time to VDD ≥ 1.8 V — — 3 ms
RST Low Time to Generate Reset tRSTL 15 — — µs
Boot Time1tboot 1 sensor — 25 — ms
2 sensors — 40 — ms
3 sensors — 55 — ms
4 sensors — 70 — ms
5 sensors — 85 — ms
6 sensors — 100 — ms
7 sensors — 115 — ms
8 sensors — 130 — ms
9 sensors — 145 — ms
10 sensors — 160 — ms
11 sensors — 175 — ms
12 sensors — 200 — ms
13 sensors — 215 — ms
Note:
1. Boot time is defined as the time from when the device enters sensing mode until the first capacitive sensing scan occurs.
3.1.4 Configuration Memory
Table 3.4. Configuration Memory
Parameter Symbol Test Condition Min Typ Max Units
Endurance (Write/Erase Cycles) NWE 20 k 100 k — Cycles
Note:
1. Data Retention Information is published in the Quarterly Quality and Reliability Report.
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 8
3.1.5 I2C Configuration Interface
Table 3.5. I2C Configuration Interface
Parameter Symbol Test Condition Min Typ Max Units
I2C Configuration Erase Delay terase — 45 — ms
I2C Configuration Write Delay twrite — 1 — ms
I2C Configuration CRC Delay tCRC — 45 — ms
I2C Configuration Validity Check
Delay
tvalid — 200 — µs
Interrupt Pin Low Time After Enter-
ing Sensing Mode
tINT_low — — 5 µs
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 9
3.1.6 Capacitive Sense
Table 3.6. Capacitive Sense
Parameter Symbol Test Condition Min Typ Max Unit
Scan Time Per Sensor1tSCAN Accumulation = 1x — 64 — µs
Accumulation = 4x — 256 — µs
Accumulation = 8x — 512 — µs
Accumulation = 16x — 1.024 — ms
Accumulation = 32x — 2.048 — ms
Accumulation = 64x — 4.096 — ms
Signal to Noise Ratio1, 2 SNR Accumulation = 1x — 90:1 — codes
Accumulation = 4x — 180:1 — codes
Accumulation = 8x — 182:1 — codes
Accumulation = 16x — 210:1 — codes
Accumulation = 32x — 230:1 — codes
Accumulation = 64x — 270:1 — codes
Conversion Time tCONV Gain = 1x — 205 — µs
Gain = 2x — 123 — µs
Gain = 3x — 98 — µs
Gain = 4x — 85 — µs
Gain = 5x — 76 — µs
Gain = 6x — 72 — µs
Gain = 7x — 67 — µs
Gain = 8x — 64 — µs
Total Processing Time3tPROC 1 sensor — 576 — µs
2 sensors — 796 — µs
3 sensors — 1.0 — ms
4 sensors — 1.2 — ms
5 sensors — 1.4 — ms
6 sensors — 1.7 — ms
7 sensors — 1.9 — ms
8 sensors — 2.1 — ms
9 sensors — 2.3 — ms
10 sensors — 2.6 — ms
11 sensors — 2.8 — ms
12 sensors — 3.0 — ms
13 sensors — 3.2 — ms
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 10
Parameter Symbol Test Condition Min Typ Max Unit
Maximum External Capacitive
Load
CEXTMAX Gain = 8x — 45 — pF
Gain = 1x — 500 — pF
Maximum External Series Impe-
dance
REXTMAX Gain = 8x — 50 — kΩ
Note:
1. Measured with gain set to 8x.
2. Measured with an evaluation board with 1/16" overlay using Capacitive Sense Profiler.
3. Sensors configured to 8x gain, 1x accumulation with sensor sampling and system processing time included.
3.1.7 IEC 60730 Safety Timing
Table 3.7. IEC 60730 Safety Timing
Parameter Symbol Test Condition Min Typ Max Unit
Test Time Between Sensing Mode
Scans
tTEST — 5 — ms
Sensing Mode Status Packet TX
Period
tSTATUS — 100 — ms
Power-On Reset Test Period tPOR_TEST — 16 — ms
3.2 Thermal Conditions
Table 3.8. Thermal Conditions
Parameter Symbol Test Condition Min Typ Max Unit
Thermal Resistance* θJA QFN24 Packages — 35 — °C/W
Note:
1. Thermal resistance assumes a multi-layer PCB with any exposed pad soldered to a PCB pad.
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 11
3.3 Absolute Maximum Ratings
Stresses above those listed in Table 3.9 Absolute Maximum Ratings on page 12 may cause permanent damage to the device. This is
a stress rating only and functional operation of the devices at those or any other conditions above those indicated in the operation list-
ings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. For
more information on the available quality and reliability data, see the Quality and Reliability Monitor Report at http://www.silabs.com/
support/quality/pages/default.aspx.
Table 3.9. Absolute Maximum Ratings
Parameter Symbol Test Condition Min Max Unit
Ambient Temperature Under Bias TBIAS –55 125 °C
Storage Temperature TSTG –65 150 °C
Voltage on VDD VDD GND–0.3 4.0 V
Voltage on I/O pins or RSTb VIN GND–0.3 VDD + 0.3 V
Total Current Sunk into Supply Pin IVDD — 400 mA
Total Current Sourced out of Ground
Pin
IGND 400 — mA
Current Sourced or Sunk by Any I/O
Pin or RSTb
IIO –100 100 mA
Maximum Total Current through all
Port Pins
IIOTOT — 200 mA
Operating Junction Temperature TJ–40 105 °C
Exposure to maximum rating conditions for extended periods may affect device reliability.
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 12
3.4 Typical Performance Curves
Figure 3.1. Active Mode Processing Time Per Sensor
Note: Active mode processing time per sensor measured with sensors configured to 1x accumulation, 8x gain. Sensor sampling and
system processing time is included.
Figure 3.2. Typical VOH Curves
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 13
Figure 3.3. Typical VOL Curves
CPT213B Data Sheet
Electrical Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 14
4. Functional Description
4.1 Capacitive Sensing Input
4.1.1 Introduction
The capacitive to digital converter uses an iterative, charge-timing self-capacitance technique to measure capacitance on an input pin.
Sampling is configured and controlled by settings in the non-volatile configuration profile, which can be changed through the 2-pin con-
figuration interface.
Baseline
Active threshold
Touch delta Inactive threshold
Capacitance
Time
Figure 4.1. Capacitive Sense Data Types
4.1.2 Touch Qualification Criteria
The device detects a touch event when an inactive (untouched) input enabled by the input enable mask detects an sequence of meas-
urements that cross the active threshold.
The device detects a touch release event when an active (touched) input enabled by the input enable mask detects an sequence of
measurements that cross the inactive threshold.
The debounce configuration profile parameter defines how many measurements in a row must cross a threshold before a touch or re-
lease is qualified. In electrically noisy environments more heavily filtered data is used for qualification.
4.1.3 Thresholds
Capacitive sensing inputs use input-specific thresholds for touch qualification. Each input uses two thresholds, one to detect inactive-to-
active transitions on the input, and another to determine active-to-inactive transitions on the input. The inputs use two thresholds to add
hysteresis and prevent active/inactive ringing on inputs. Each threshold can be set through Simplicity Studio tools and all thresholds are
stored in non-volatile memory in the device's configuration profile.
Thresholds are defined as percentages of a capacitive sensing input's touch delta.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 15
4.1.4 Debounce Counter
Each capacitive sensing input maintains its own debounce counter. For an inactive sensor, this counter tracks the number of succes-
sive samples which have crossed that input's active threshold. For an active sensor, this counter tracks the number of successive sam-
ples which have crossed the inactive threshold. When the counter reaches a terminal value defined in the the configuration profile, the
touch/release event is qualified.
4.1.5 Touch Deltas
Each capacitive sensing input uses a stored touch delta value that describes the expected difference between inactive and active ca-
pacitive sensing output codes. This value is stored in the configuration profile for the system and is used by the touch qualification en-
gine, which defines inactive and active thresholds relative to the touch delta.
The touch deltas are stored in the configuration profile in a touch delta/16 format. For this reason, touch deltas must be configured as
multiples of 16.
4.1.6 Auto-Accumulation and Averaging
Capacitive sensing inputs have an auto-accumulate and average post-sample filter that can be used to improve signal strength if nee-
ded. Settings stored in the configuration profile can configure the engine to accumulate 1, 4, 8, 16, 32, or 64 samples. After the defined
number of samples have been accumulated, the result is divided by either 1, 4, 8, 16, 32, or 64, depending on the accumulation setting.
This auto-accumulated and averaged value is the sample output used for all touch qualification processing. Note that sample time per
sensor increases as the level of accumulation increases. To reduce current consumption, the engine should not be set to auto-accumu-
late unless it is required to achieve acceptable signal strength due to thick overlays or other system-level factors.
4.1.7 Drive Strength
The drive strength of the current source used to charge the electrode being measured by the capacitive sensing input can be adjusted
in integer increments from 1x to 8x (8x is the default). High drive strength gives the best sensitivity and resolution for small capacitors,
such as those typically implemented as touch-sensitive PCB features. To measure larger capacitance values, the drive strength should
be lowered accordingly. The highest drive strength setting that yields capacitive sensing output which does not saturate the sensing
engine when the electrode is active (touched) should always be used to maximize input sensitivity.
4.1.8 Active Mode Scan Enable
Active mode scanning of capacitive sensing inputs is controlled by an enable setting for each capacitive sensing input. This setting is
stored in the configuration profile.
4.1.9 Active Mode Scanning
Once in sensing mode, the device continuously samples all enabled sensors. The device filters and processes each sample and quali-
fies touch events when detected. Qualified touch events and release events are expressed to the host through event buffer packets,
which the host reads across the I2C interface after the device signals by activating the interrupt pin.
4.1.10 No Confidence Mode
The device uses each sensor's sample to incrementally update an interference characterization metric. This metric controls filtering ag-
gressiveness on samples fed into the touch qualification engine. If system-level interference is characterized by the device as being of a
magnitude that prevents reliable touch qualification, the device disqualifies any currently-qualified touches, sending touch release event
packets.
No confidence mode entrance is expressed to the host in a status event packet. The host must initiate the query to the CPT213B to
determine the device's current status.
Once the device determines that no confidence mode can be exited, the status event packet will reflect this change. After exiting no
confidence mode, touch qualification resumes.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 16
4.1.11 IEC60730 Functionality
Once in sensing mode, the device periodically executes IEC60730 safety and plausibility checks on timing, memory, and hardware. If
any of these plausibility checks fail, the device immediately enters a safe state that disables capacitive sensing and the I2C interface.
Once the device enters a safe state, it will remain in this safe state until a hardware reset using the RSTb pin or power-on reset.
The host communicating with the device is responsible for checking for the presence of status packets. If no status packet has been
presented on the I2C bus by the device within two periods of expected status packet transmission, the host should assume that the
CPT213B is in a safe state and respond accordingly. The typical expected status packet transmission period is 100 ms.
The device performs a periodic analog plausibility check on each enabled sensor. A sensor trace that has been damaged such that it is
shorted to ground or the supply will be detected during this plausibility check, and the device will enter safe state.
4.2 I2C Event Buffer Interface
4.2.1 Introduction
The event buffer I2C interface provides an event-driven, packetized communication system describing newly qualified events generated
by the capacitive sensing input engine. The supported packet structure includes safetey features adhering to IEC 60730 compliance
specification. The interface runs in one of two mutually exclusive modes: sensing mode and configuration loading mode, where a new
configuration profile can be downloaded to the device and stored in non-volatile memory.
In sensing mode, the interface provides access to a first-in-first-out buffer of data packets. When the sensing engine generates these
packets and pushes them onto the buffer, the interface then signals the host to indicate that one or more packets are available in the
buffer by activating the event buffer interrupt pin.
In sensing mode, the interrupt pin is defined as active-low and operates as a push-pull digital output. In configuration loading mode, the
interrupt pin is configured as a digital input and functions as a chip select. I2C transactions will be ignored by the device unless the host
has pulled the interrupt pin low before sending the start condition.
The host reads the packets through an I2C interface, with the host acting as an I2C master. Once all packets have been fully transmit-
ted across the I2C interface, the event buffer interrupt pin is de-activated. The device will remain in active mode until no packets remain
in the buffer, even if no sensors have been qualified as active for the period of time defined by the active mode scan period.
In configuration loading mode, the interface enables an in-system programming initiated by the host. In this mode, the host can update
the performance configuration space.
4.2.2 Startup Behavior
When the device exits a POR or hardware reset, it first enters configuration loading mode, discussed in detail 4.2.12 Configuration
Loading Procedure. A host can command the device to enter sensing mode using the mode selection command discussed in
4.2.10 Entering Sensing Mode from Configuration Loading Mode. If the device has a valid configuration profile stored in non-volatile
memory, the device will then enter sensing mode and remain in this mode until the next power cycle or reset.
The device runs a number of safety checks immediately after exiting reset, including checks to memory and other core features. If any
safety or plausibility test fails, the device enters safe state. A host can assume the device is in safe state if it is no longer responding to
any I2C transactions.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 17
4.2.3 Sensing Mode Event Packet Structure
Every qualified event detected by the capacitive sensing input engine generates a single packet that can be retrieved by the host pro-
cessor through the event buffer I2C interface. The packet is an atomic data unit that fully describes the generated event.
In addition to including touch sensing information, each packet includes IEC 60730 safety compliance bytes that must be received and
examined by the host.
Note: The bytes in the packet are transmitted MSB first.
Each packet has a standard structure that can be parsed by the host.
Table 4.1. Standard Packet Structure
Byte # Designator
0 I2C Slave Address + read bit
1 I2C Slave Address (repeat with LSB = 0)
2 Packet counter and event type
3 Event description (byte 1)
4 Event description (byte 2)
5 CRC (MSB)
6 CRC (LSB)
The packet counter is a 4-bit number stored in the upper bits of byte 2. Each new event will be assigned a counter value that is +1 from
the last qualified event. After event 15, the counter wraps back to 0 for the next event. The counter captures the temporal nature of
touch events so that a host can reconstruct a sequence of events over time. Also, the host can use the counter value to determine if a
packet has been lost due to a buffer overflow. The event buffer counter is reset to 0 upon entrance to sensing mode.
The event type is a 4-bit value describes the originator of the event. For instance, the source could be a capacitive sensing button. The
event type is stored in the lower 4 bits of byte 2.
The event description bytes define characteristics of the event that have been qualified. Event descriptions are defined relative to the
event source. An event source that is a capacitive sensing input will have a defined set of valid event description values. Those same
values will mean something different for a different type of event source. Event description values are defined relative to the event type
field of byte 2.
Touch
Event
I2C Slave Address
+ read bit
CSxx
index 0x00
byte 0 byte 2 byte 3 byte 4
Touch
Release
Event
I2C Slave Address
+ read bit
CSxx
index 0x00
byte 0 byte 2 byte 3 byte 4
packet
counter
xxxx
event
type
0000
packet
counter
xxxx
event
type
0001
I2C Slave Address
(repeat) + LSB = 0
byte1
I2C Slave Address
(repeat) + LSB = 0
byte1
Status
Event
I2C Slave Address
+ read bit Status
byte 0 byte 2 byte 3
packet
counter
xxxx
event
type
1111
I2C Slave Address
(repeat) + LSB = 0
byte1
byte 5 byte 6
16-bit CRC
(MSB)
16-bit CRC
(LSB)
byte 5 byte 6
16-bit CRC
(MSB)
16-bit CRC
(LSB)
0x00
byte 4 byte 5 byte 6
16-bit CRC
(MSB)
16-bit CRC
(LSB)
Figure 4.2. I2C Event Buffer Packet Structure
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 18
The I2C Slave Address and read bit are repeated in byte 1 as required by the IEC 60730 standard. The address is left shifted to fill bits
7-1, and the LSB is cleared to 0.
The CSxx index transmitted in byte 3 for Touch and Touch Release events enables the host processor to determine the sensor that
caused the event.
In both sensing mode and config loader mode, packets transferred across I2C include a 16-bit CRC in the last two bytes. More informa-
tion on the algorithm used for this CRC calculation can be found in 4.2.4 CRC Algorithm. For each transaction, these CRCs include
byte 1 and end before the two CRC bytes at the end of the packet. Both master read and master write transactions must follow this
structure. Master write transactions sent to the device in configuration mode with incorrect CRCs will result in a safe state entrance
upon any attempt to execute the mode selection command to switch to sensing mode.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 19
4.2.4 CRC Algorithm
The CRC is generated using the standard CCITT-16 16-bit polynomial (0x1021) with an initial seed of 0xFFFF.
The device generates a 16-bit CRC result equivalent to the following algorithm:
1. XOR the input with the most-significant bits of the current CRC result. If this is the first iteration of the CRC unit, the current CRC
result will be the set initial value (0x0000 or 0xFFFF).
2. If the MSB of the CRC result is set, shift the CRC result and XOR the result with the polynomial.
3. If the MSB of the CRC result is not set, shift the CRC result.
4. Repeat steps 2 and 3 for all 8 bits.
The algorithm is also described in the following example.
unsigned short UpdateCRC (unsigned short CRC_acc, unsigned char CRC_input)
{
unsigned char i; // loop counter
#define POLY 0x1021
// Create the CRC "dividend" for polynomial arithmetic (binary arithmetic
// with no carries)
CRC_acc = CRC_acc ^ (CRC_input << 8);
// "Divide" the poly into the dividend using CRC XOR subtraction
// CRC_acc holds the "remainder" of each divide
//
// Only complete this division for 8 bits since input is 1 byte
for (i = 0; i < 8; i++)
{
// Check if the MSB is set (if MSB is 1, then the POLY can "divide"
// into the "dividend")
if ((CRC_acc & 0x8000) == 0x8000)
{
// if so, shift the CRC value, and XOR "subtract" the poly
CRC_acc = CRC_acc << 1;
CRC_acc ^= POLY;
}
else
{
// if not, just shift the CRC value
CRC_acc = CRC_acc << 1;
}
}
// Return the final remainder (CRC value)
return CRC_acc;
}
The following table lists several input values and the associated outputs using this 16-bit CRC algorithm:
Table 4.2. Example 16-bit CRC Outputs
Input Output
0x63 0xBD35
0x8C 0xB1F4
0x7D 0x4ECA
0xAA, 0xBB, 0xCC 0x6CF6
0x00, 0x00, 0xAA, 0xBB, 0xCC 0xB166
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 20
4.2.5 Packet Retrieval in Sensing Mode
When the least significant byte of an event packet has been transferred during a master read transaction, that event is popped from the
device's buffer. If only a part of the event is read, the event will stay in the buffer and will be transmitted again by the device during the
next read.
If the host initiates a master read when the device is in sensing mode but the interrupt pin is not active, signifying that the device has no
events in its buffer to transmit, the device will NACK its slave address on the bus.
If the I2C master sends a stop condition on the bus before the entire packet has been read, the device will not pop the packet from its
internal buffer. Instead, the I2C state machine will reset, and the next transaction will begin with the first byte of the same event that
was being read in the previous, prematurely-terminated transaction.
The I2C event buffer has a depth of 16 events. If the host does not read events promptly after seeing the interrupt pin go active, there is
the possibility of a buffer overflow. In the event of an overflow, the device will enter safe state.
New I2C packets will only be generated at the active mode sample rate, and so the buffer will fill a maximum of 13 packets (in the case
simultaneous touch/releases) per sample period. If the host runs the I2C bus at 400 kHz and reads packets as soon as the interrupt pin
activates, all packets can be read from the buffer in 1 to 2 ms, which is faster than the rate at which a new active mode scan sequence
can complete.
4.2.6 Defined Event Types
The device assigns the following event types:
Table 4.3. Event Type Mapping
Event Type Value Mapping
Sensing Mode
0 (0x0) Sensor activity - touch event
1 (0x1) Sensor activity - release event
15 (0xF) Status packet
Configuration Loading Mode
8 (0x8) Mode selection
9 (0x9) Configuration unlock
10 (0xA) Configuration erase
11 (0xB) Write configuration
12 (0xC) Write CRC
Note that this event type value is stored in the lower 4 bits of the first non-address byte of a packet. The upper 4 bits are a packet
counter value.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 21
4.2.7 Description Bytes for Touch Events
A touch or release event uses only one byte of the description field. That field identifies which sensor caused the touch or release event
as shown below.
Table 4.4. Touch or Release Event Sensor Mapping
Value Mapping
0 Capacitive sensing input 0
1 Capacitive sensing input 1
2 Capacitive sensing input 2
3 Capacitive sensing input 3
4 Capacitive sensing input 4
5 Capacitive sensing input 5
6 Capacitive sensing input 6
7 Capacitive sensing input 7
8 Capacitive sensing input 8
9 Capacitive sensing input 9
10 Capacitive sensing input 10
11 Capacitive sensing input 11
12 Capacitive sensing input 12
4.2.8 Description Bytes for Status Events
The I2C event buffer transmits a status packet periodically when in sensing mode. Because configuration loading mode is considered to
be a safe state, status packets are not transmitted when in configuration loading mode. This packet is used by the host to determine
that the TouchXpress device is operational and not halted in its safe state.
For status events, both event description bytes are 0x00, except that bit 0 of the MSB event description will be set to 1 if the sensor
goes into 'no confidence mode' where touch qualification is temporarily prohibited due to interference conditions.
Table 4.5. Status Packet Mapping
Event Description Bit Status Indicator
MSB 7-1 Reserved
0 0 – sensing is functional
1 – sensing is temporarily disabled because of no confidence mode entrance
LSB 7-0 Reserved
If the TouchXpress device has not offered to transmit a status packet within the defined time limit, the host must consider the I2C de-
vice in a safe state and respond accordingly.
4.2.9 Slave Address
When the device comes out of reset and has not been commanded to enter sensing mode, the device responds to the slave address
0xC0. Additionally, the device will only respond to commands with address 0xC0 if the host drives the interrupt pin low, using the pin as
a chip select.
In sensing mode, the device responds to I2C transactions addressed to the slave address stored in the configuration profile.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 22
4.2.10 Entering Sensing Mode from Configuration Loading Mode
Upon exiting reset, the device enters configuration loading mode. During this time, a host can re-write the configuration profile through a
sequence of master write commands. The host can also command the device to enter sensing mode using the mode selection com-
mand. The mode switch command is structured as shown in the following figure.
Mode Selection 0xC0 + write bit
byte 0
Note: The INT pin must be driven low prior to the I2C start and high after the I2C stop.
0xC0 (repeat) +
LSB = 0
byte 2
packet
counter
xxxx
event
type
1000
byte 3
0x01
byte 4 byte 5
16-bit CRC
(MSB)
16-bit CRC
(LSB)
byte 1
Figure 4.3. Mode Selection Command
The device will only enter sensing mode if the configuration profile stored in non-volatile memory is valid. The validity of the configura-
tion profile can be checked using the Configuration Profile Validity Check command.
If a mode selection call is made on a device where the configuration is not currently valid, the device will enter safe state and not re-
spond to any further I2C transactions.
Note that this mode setting feature must be executed once per device, per reset. Until this command has been received by a device,
the device will remain in its startup state, executing periodic IEC checks but not performing any touch qualification.
4.2.11 Determining Configuration Validity
At any point when the device is in configuration loading mode, the host can issue a Configuration Profile Validity Check command. This
command is issued when the host starts a master read command. This command is unique in that it does not include a byte containing
the packet counter or event type.
Configuration Profile
Validity Check
byte 1
0xC0 + read bit
byte 0
Note: The INT pin must be driven low prior to the I2C start and high after the I2C stop.
0xC0 (repeat) +
LSB = 0
byte 2
Configuration
Profile State
byte 3 byte 4
16-bit CRC
(MSB)
16-bit CRC
(LSB)
Note: This is a read transaction where data is provided from the CPT device.
Figure 4.4. Configuration Profile Validity Check Command
Table 4.6. Decoding the Configuration Profile State
Value Description
0x80 Configuration profile valid
0x01 Configuration profile invalid
The validity of the configuration profile is determined by comparing a CRC stored in non-volatile memory to a CRC generated at runtime
by the device. The CRC is calculated using the algorithm described in 4.2.4 CRC Algorithm.
Note: The CRC for the configuration profile spans 510 bytes, with 0xFF padding in addresses above any non-0xFF configuration profile
bytes.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 23
4.2.12 Configuration Loading Procedure
Once the device has been configured to configuration bootload mode, the I2C interface can accept and process the bootload command
set. The bootloading procedure executes as follows in the steps below. Valid bootload mode commands are shown below.
It is recommended that the host control the device's reset pin. Reset should be strobed before the configuration loading procedure be-
gins. If multiple TouchXpress devices are being used in the system, all devices could be shorted to the same reset pin and strobed
simultaneously for config loading and sensing mode re-entrance.
1. Host sends the configuration loading unlock sequence.
2. Host sends config erase command, which erases the configuration profile. Packet should be resent until device ACKs reception.
3. Host sends bytes 0-7 of configuration profile in a write config command. Packet resent until device ACKs reception.
4. Host repeats process of the previous step, sending the next 8 bytes of the config profile in a write config command, resending until
packet is ACKed.
5. After all 8-byte packets of the configuration profile have been transmitted to the device and ACKed by the device, host sends write
CRC command. This CRC uses the algorithm described in 4.2.4 CRC Algorithm.
6. Host sends a mode switch command to enter sensing mode.
Once the device has successfully entered sensing mode after a mode switch command, the device will remain in sensing mode until a
hardware reset.
The packet counter is not used in configuration loading mode. Those 4 bits can be set to any value as long as the contents of the byte
equal the value used as part of the packet CRC.
Configuration
Unlock
0xC0 + write bit
byte 0 byte 2
packet
counter
xxxx
event
type
1001
0xC0 (repeat) +
LSB = 0
byte 1 byte 5 byte 6
0xA5
byte 3
0xF1
byte 4
Configuration
Erase
0xC0 + write bit
byte 0 byte 2
packet
counter
xxxx
event
type
1010
0xC0 (repeat) +
LSB = 0
byte 1
16-bit CRC
(MSB)
byte 3
16-bit CRC
(LSB)
byte 4
Write CRC 0xC0 + write bit
byte 0 byte 2
packet
counter
xxxx
event
type
1100
0xC0 (repeat) +
LSB = 0
byte 1 byte 5 byte 6
Config
Profile CRC
MSB
byte 3
Config
Profile CRC
LSB
byte 4
Configuration
Profile Validity
Check
0xC0 + read bit
byte 0 byte 2
0xC0 (repeat) +
LSB = 0
byte 1 byte 3 byte 4
Write
Configuration
0xC0 + write bit
byte 0 byte 2
packet
counter
xxxx
event
type
1011
0xC0 (repeat) +
LSB = 0
byte 1 byte 11 byte 12
xx
byte 3
xx
byte 4
... xx
byte 9
xx
byte 10
16-bit CRC
(MSB)
16-bit CRC
(LSB)
16-bit CRC
(MSB)
16-bit CRC
(LSB)
16-bit CRC
(MSB)
16-bit CRC
(LSB)
16-bit CRC
(MSB)
16-bit CRC
(LSB)
Configuration
Profile State
Note: The INT pin must be driven low prior to the I2C start and high after the I2C stop for each of these commands.
Figure 4.5. Configuration Loading Command Sequence
4.3 Configuration Profile
The configuration interface is used by the device to configure default values and performance characteristics that effect capacitive
sensing. The configuration data can be programmed through the Configuration interface (Config Clk and Config Data pins) using
[Xpress Configurator] in Simplicity Studio or through the I2C interface from the host processor.
Several configuration profile templates are available in Simplicity Studio to provide a starting point for development.
CPT213B Data Sheet
Functional Description
silabs.com | Building a more connected world. Rev. 1.1 | 24
5. Pin Definitions
5.1 CPT213B QFN24 Pin Definitions
GND
24
23
22
21
20
19
1
2
3
4
5
6
7
8
9
10
11
12
18
17
16
15
14
13
24 pin QFN
(Top View)
N/C
GND
VDD
N/C
N/C
RSTb /
Config Clk
Config Data
EB_INT
EB_SCL
N/C
EB_SDA
CS12
CS06
CS07
CS08
CS09
CS10
CS11
CS00
CS01
CS02
CS03
CS04
CS05
Figure 5.1. CPT213B QFN24 Pinout
Table 5.1. Pin Definitions for CPT213B QFN24
Pin
Number
Pin Name Description
1 N/C No connect
2 GND Ground
3 VDD Supply power input
4 N/C No connect
5 N/C No connect
CPT213B Data Sheet
Pin Definitions
silabs.com | Building a more connected world. Rev. 1.1 | 25
Pin
Number
Pin Name Description
6 RSTb /
Config Clk
Active-low reset /
Configuration clock
7 Config Data Configuration data
8 EB_INT Push-pull digital output
Event buffer interrupt pin
9 EB_SCL Open drain digital output
Event buffer I2C SCL
10 N/C No connect
11 EB_SDA Open drain digital input
Event buffer I2C SDA
12 CS12 Analog input
Capacitive sensing input 12
13 CS11 Analog input
Capacitive sensing input 11
14 CS10 Analog input
Capacitive sensing input 10
15 CS09 Analog input
Capacitive sensing input 9
16 CS08 Analog input
Capacitive sensing input 9
17 CS07 Analog input
Capacitive sensing input 7
18 CS06 Analog input
Capacitive sensing input 6
19 CS05 Analog input
Capacitive sensing input 5
20 CS04 Analog input
Capacitive sensing input 4
21 CS03 Analog input
Capacitive sensing input 3
22 CS02 Analog input
Capacitive sensing input 2
23 CS01 Analog input
Capactive sensing input 1
24 CS00 Analog input
Capacitive sensing input 0
CPT213B Data Sheet
Pin Definitions
silabs.com | Building a more connected world. Rev. 1.1 | 26
6. QFN24 Package Specifications
6.1 QFN24 Package Dimensions
Figure 6.1. QFN24 Package Drawing
Table 6.1. QFN24 Package Dimensions
Dimension Min Typ Max
A 0.70 0.75 0.80
A1 0.00 0.02 0.05
b 0.18 0.25 0.30
D 4.00 BSC
D2 2.55 2.70 2.80
e 0.50 BSC
E 4.00 BSC
E2 2.55 2.70 2.80
L 0.30 0.40 0.50
L1 0.00 — 0.15
aaa — — 0.15
bbb — — 0.10
CPT213B Data Sheet
QFN24 Package Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 27
Dimension Min Typ Max
ddd — — 0.05
eee — — 0.08
Z — 0.24 —
Y — 0.18 —
Note:
1. All dimensions shown are in millimeters (mm) unless otherwise noted.
2. Dimensioning and Tolerancing per ANSI Y14.5M-1994.
3. This drawing conforms to JEDEC Solid State Outline MO-220, variation WGGD except for custom features D2, E2, Z, Y, and L
which are toleranced per supplier designation.
4. Recommended card reflow profile is per the JEDEC/IPC J-STD-020C specification for Small Body Components.
CPT213B Data Sheet
QFN24 Package Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 28
6.2 PCB Land Pattern
Figure 6.2. PCB Land Pattern Drawing
Table 6.2. PCB Land Pattern Dimensions
Dimension Min Max
C1 3.90 4.00
C2 3.90 4.00
E 0.50 BSC
X1 0.20 0.30
X2 2.70 2.80
Y1 0.65 0.75
Y2 2.70 2.80
Note:
1. All dimensions shown are in millimeters (mm) unless otherwise noted.
2. This Land Pattern Design is based on the IPC-7351 guidelines.
3. All metal pads are to be non-solder mask defined (NSMD). Clearance between the solder mask and the metal pad is to be 60 µm
minimum, all the way around the pad.
4. A stainless steel, laser-cut and electro-polished stencil with trapezoidal walls should be used to assure good solder paste release.
5. The stencil thickness should be 0.125 mm (5 mils).
6. The ratio of stencil aperture to land pad size should be 1:1 for all perimeter pads.
7. A 2 x 2 array of 1.10 mm x 1.10 mm openings on 1.30 mm pitch should be used for the center ground pad.
8. A No-Clean, Type-3 solder paste is recommended.
9. The recommended card reflow profile is per the JEDEC/IPC J-STD-020 specification for Small Body Components.
CPT213B Data Sheet
QFN24 Package Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 29
6.3 Package Marking
CPT213B
TTTTTT
YYWW
Figure 6.3. Package Marking
The package marking consists of:
• CPT213B – The part number designation.
• TTTTTT – A trace or manufacturing code. The first letter of this code is the hardware revision.
• YY – The last two digits of the assembly year.
• WW – The 2-digit workweek when the device was assembled.
CPT213B Data Sheet
QFN24 Package Specifications
silabs.com | Building a more connected world. Rev. 1.1 | 30
7. Relevant Application Notes
The following Application Notes are applicable to the CPT213B devices:
•AN957: TouchXpress™ Configuration and Profiling Guide — This application note guides developers through the evaluation and
configuration process of TouchXpress devices using Simplicity Studio [Xpress Configurator] and [Capacitive Sense Profiler].
•AN447: Printed Circuit Design Notes for Capacitive Sensing Performance — This document describes hardware design guidelines
specifically for capacitive sensing applications, including button placement and other layout guidelines.
•AN949: TouchXpress™ Programming Guide — This application note discusses the production programming options available for
TouchXpress devices.
•AN1074: EFM8 Family IEC60730 Library — This application note discusses how to create systems that are IEC compliant. This
process will be required for the host talking to the CPT213B device.
Application Notes can be accessed on the Silicon Labs website (www.silabs.com/interface-appnotes) or in Simplicity Studio in the [Doc-
umentation]>[Application Notes] area.
CPT213B Data Sheet
Relevant Application Notes
silabs.com | Building a more connected world. Rev. 1.1 | 31
8. Revision History
8.1 Revision 1.1
June 30th, 2017
Updated the Power-On Reset Test Period typical value in 3.1.7 IEC 60730 Safety Timing.
Added 3.1.5 I2C Configuration Interface.
8.2 Revision 1.0
May 10th, 2017
Initial release.
CPT213B Data Sheet
Revision History
silabs.com | Building a more connected world. Rev. 1.1 | 32
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