Texas Instruments TI Designs Reference

Ajinder Singh, Natarajan Viswanathan

TI Designs

Wireless Heart Rate Monitor Reference Design

TI Designs Design Features

TI Designs provide the foundation that you need The Wireless Heart Rate Monitor with Bluetooth® low­including methodology, testing and design files to energy (BLE) is a reference design for customers to
quickly evaluate and customize and system. TI develop end-products for battery-powered 3-channel
Designs help you accelerate your time to market. health and fitness electrocardiogram (ECG)

Design Resources

TIDA-00096
ADS1293 Product Folder
CC2541 Product Folder
TPS61220 Product Folder

CC Debugger

Tool Folder Containing Design Files

Small Programmer and Debugger for
Low-Power RF System-on-Chips

applications.

• Supports 5-Lead ECG applications

• Easily monitor heart rate data through an iOS
Mobile Application

• Powered by a Lithium-ion battery

• EMI filters integrated in the ADS1293 device reject
Interference from outside RF sources

• Open-source Firmware and iOS application
enables quick time-to-market for customers

Featured Applications

• Health and Fitness

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System Description

1 System Description

The heart of the Wireless Heart Rate Monitor is the ADS1293 device (analog front-end) and the CC2541
device (Bluetooth-low energy SOC) as shown in Figure 1. The ADS1293 device is a highly integrated low­power analog front-end (AFE) that features three high-resolution ECG channels. The CC2541 system-on­chip (SoC) adds a BLE wireless feature to the platform. BLE enables seamless connectivity to an iPhone®
or an iPad® through a configurable iOS application that allows an end-user to remotely monitor the heart­rate data of a patient.

1.1 ADS1293

The ADS1293 incorporates all features commonly required in portable, low-power medical, sports, and
fitness electrocardiogram (ECG) applications. With high levels of integration and exceptional performance,
the ADS1293 enables the creation of scalable medical instrumentation systems at significantly reduced
size, power, and overall cost.

The ADS1293 features three high-resolution channels capable of operating up to 25.6ksps. Each channel
can be independently programmed for a specific sample rate and bandwidth allowing users to optimize the
configuration for performance and power. All input pins incorporate an EMI filter and can be routed to any
channel via a flexible routing switch. Flexible routing also allows independent lead-off detection, right leg
drive, and Wilson/Goldberger reference terminal generation without the need to reconnect leads
externally. A fourth channel allows external analog pace detection for applications that do not utilize digital
pace detection. For the ADS1293 block diagram, see Figure 2.

The ADS1293 incorporates a self-diagnostics alarm system to detect when the system is out of the
operating conditions range. Such events are reported to error flags. The overall status of the error flags is
available as a signal on a dedicated ALARMB pin. The device is packaged in a 5-mm × 5-mm × 0,8-mm,
28-pin LLP. Operating temperature ranges from –20°C to 85°C.

www.ti.com

1.2 CC2541

The CC2541 is a power-optimized true system-on-chip (SoC) solution for both Bluetooth low energy and
proprietary 2.4-GHz applications. It enables robust network nodes to be built with low total bill-of-material
costs. The CC2541 combines the excellent performance of a leading RF transceiver with an industry­standard enhanced 8051 MCU, in-system programmable flash memory, 8-KB RAM, and many other
powerful supporting features and peripherals. The CC2541 is highly suited for systems where ultralow
power consumption is required. This is specified by various operating modes. Short transition times
between operating modes further enable low power consumption.

The CC2541 is pin-compatible with the CC2540 in the 6-mm × 6-mm QFN40 package, if the USB is not
used on the CC2540 and the I2C/extra I/O is not used on the CC2541. Compared to the CC2540, the
CC2541 provides lower RF current consumption. The CC2541 does not have the USB interface of the
CC2540, and provides lower maximum output power in TX mode. The CC2541 also adds a HW I2C
interface.

The CC2541 is pin-compatible with the CC2533 RF4CE-optimized IEEE 802.15.4 SoC. The CC2541
comes in two different versions: CC2541F128/F256, with 128 KB and 256 KB of flash memory,
respectively. For the CC2541 block diagram, see Figure 3.

1.3 TPS61220

The TPS6122x family devices provide a power-supply solution for products powered by either a single­cell, two-cell, or three-cell alkaline, NiCd or NiMH, or one-cell Li-Ion or Li-polymer battery. Possible output
currents depend on the input-to-output voltage ratio. The boost converter is based on a hysteretic
controller topology using synchronous rectification to obtain maximum efficiency at minimal quiescent
currents. The output voltage of the adjustable version can be programmed by an external resistor divider,
or is set internally to a fixed output voltage. The converter can be switched off by a featured enable pin.
While being switched off, battery drain is minimized. The device is offered in a 6-pin SC-70 package
(DCK) measuring 2 mm × 2 mm to enable small circuit layout size. For the TPS61220 block diagram, see

Figure 4.

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ADS1293

Analog Front End

CC2541

ADC + uP + BLE

TPS61220

Boost Converter

Battery

www.ti.com

2 Block Diagram

Figure 1. Temperature Transmitter System Block Diagram

2.1 Highlighted Products

The Wireless Heart Rate Monitor Reference Design features the following devices:

• ADS1293
– ADS1293 Low Power, 3-Channel, 24-Bit Analog Front End for Biopotential Measurements

• CC2541
– 2.4-GHz Bluetooth™ low energy and Proprietary System-on-Chip

• TPS61220
– TPS6122x Low Input Voltage, 0.7V Boost Converter With 5.5μA Quiescent Current

For more information on each of these devices, see the respective product folders at www.TI.com.

Block Diagram

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CH1-ECG

CH2-ECG

CH3-ECG

Lead off

detect

-

+

EMI
filter

CSB

SCLK

SDI

SDO

OSC

IN1

Flexible
Routing

Switch

Test

Ref

XTAL1

-

+

VSS

VDD

VDDIO

CVREF

RLDINV

RLDIN

EMI
filter

IN2

EMI
filter

IN3

EMI
filter

IN4

EMI
filter

IN5

EMI
filter

IN6

Batt.
Mon

CMOUT

XTAL2

POR

RSTB

DRDYB

RLDREF

CLK

ALARMB

DIGITAL

CONTROL AND

POWER

MANAGEMENT

Wilson

ref.

CM

Detect

SYNCB

VSSIO

Digital

Filter

Σ∆

Modulator

Digital

Filter

Σ∆

Modulator

-

+

-

+

InA

InA

InA

WCT

-

+

CH4- Analog Pace

WILSON_EN

CMDET_EN

SELRLD

REF

EMI

filter

EMI

filter

LOD_EN

CH1-Pace

CH2-Pace

CH3-Pace

Digital

Filter

Σ∆

Modulator

REF for

CM & RLD

RLD

Amp.

PACE2

RLDIN

PACE2WCT

WILSON_CN

CH1

CH2

CH3

CH4 InA

Block Diagram

2.1.1 ADS1293

• Low current consumption:
– Duty-Cycle mode: 120 μA
– Normal mode: 415 μA

• Wide supply range: 2.3 V to 5.5 V

• Programmable gain: 1 V/V to 128 V/V

• Programmable data rates: Up to 2 kSPS

• 50-Hz and 60-Hz rejection at 20 SPS

• Low-noise PGA: 90 nV

• Dual matched programmable current sources: 10 μA to 1500 μA

• Internal temperature sensor: 0.5°C Error (max)

• Low-drift internal reference

• Low-drift internal oscillator

• Two differential or four single-ended inputs

• SPI™-compatible interface

• 3,5 mm × 3,5 mm × 0,9 mm QFN package

Figure 2. ADS1293 Block Diagram

at 20 SPS

RMS

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SFR bus SFR bus

MEMORY

ARBITRATOR

8051 CPU

CORE

DMA

FLASH

SRAM

FLASH CTRL

DEBUG

INTERFACE

RESET

RESET_N

P2_4

P2_3

P2_2

P2_1

P2_0

P1_4

P1_3

P1_2

P1_1

P1_0

P1_7

P1_6

P1_5

P0_4

P0_3

P0_2

P0_1

P0_0

P0_7

P0_6

P0_5

32.768 kHz

CRYSTAL OSC

32 MHz

CRYSTAL OSC

HIGH SPEED

RC-OSC

32 kHz

RC-OSC

CLOCK MUX &
CALIBRATION

RAM

USART 0

USART 1

TIMER 1 (16-bit)

TIMER 3 (8-bit)

TIMER 2

(BLE LL TIMER)

TIMER 4 (8-bit)

AES

ENCRYPTION

&

DECRYPTION

WATCHDOG TIMER

IRQ

CTRL

FLASH

UNIFIED

RF_P RF_N

SYNTH

MODULATOR

POWER ON RESET

BROWN OUT

RADIO

REGISTERS

POWER MGT. CONTROLLER

SLEEP TIMER

PDATA

XRAM

IRAM

SFR

XOSC_Q2

XOSC_Q1

DS ADC

AUDIO / DC

DIGITAL

ANALOG

MIXED

VDD (2.0 - 3.6 V)

DCOUPL

ON-CHIP VOLTAGE

REGULATOR

Link Layer Engine

FREQUENCY

SYNTHESIZER

I2C

DEMODULATOR

RECEIVE TRANSMIT

OP-AMP

ANALOG COMPARATOR

I/O CONTROLLER

1 KB SRAM

Radio Arbiter

FIFOCTRL

SDA

SCL

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2.1.2 CC2541

Block Diagram

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Figure 3. CC2541 Block Diagram

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Block Diagram

• RF
– 2.4-GHz Bluetooth low energy Compliant and Proprietary RF System-on-Chip
– Supports 250-kbps, 500-kbps, 1-Mbps, 2-Mbps Data Rates
– Excellent link budget, enabling long-range applications without external front end
– Programmable output power up to 0 dBm
– Excellent receiver sensitivity (–94 dBm at 1 Mbps), selectivity, and blocking performance
– Suitable for systems targeting compliance with worldwide radio frequency regulations: ETSI EN 300

• Layout
– Few external components
– Reference design provided
– 6-mm × 6-mm QFN-40 package
– Pin-compatible with CC2540 (when not using USB or I2C)

• Low Power
– Active-mode RX down to: 17.9 mA
– Active-mode TX (0 dBm): 18.2 mA
– Power mode 1 (4-µs wake-up): 270 µA
– Power mode 2 (sleep timer on): 1 µA
– Power mode 3 (external interrupts): 0.5 µA
– Wide Supply-voltage range (2 V–3.6 V)

• TPS62730 Compatible low power in active mode
– RX down to: 14.7 mA (3-V supply)
– TX (0 dBm): 14.3 mA (3-V supply)

• Microcontroller
– High-performance and low-power 8051 microcontroller core with code Prefetch
– In-system-programmable flash, 128- or 256-KB
– 8-KB RAM with retention in all power modes
– Hardware-debug support
– Extensive baseband automation, including auto-acknowledgment and address decoding
– Retention of all relevant registers in all power modes

• Peripherals
– Powerful five-channel DMA
– General-purpose timers (one 16-Bit, two 8-Bit)
– IR generation circuitry
– 32-kHz sleep timer with capture
– Accurate digital RSSI support
– Battery monitor and temperature sensor
– 12-Bit ADC with eight channels and configurable resolution
– AES security coprocessor
– Two powerful USARTs with support for several serial protocols
– 23 general-purpose I/O Pins (21 × 4 mA, 2 × 20 mA)
– I2C interface
– Two I/O pins have LED Driving capabilities
– Watchdog timer
– Integrated high-performance comparator

• Development Tools

www.ti.com

328 and EN 300 440 Class 2 (Europe), FCC CFR47 Part 15 (US), and ARIB STD-T66 (Japan)

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• Software Features

Block Diagram

– CC2541 evaluation module kit (CC2541EMK)
– CC2541 mini development kit (CC2541DK-MINI)
– SmartRF™ software
– IAR embedded Workbench™ available

– Bluetooth v4.0 compliant protocol stack for single-mode BLE solution

• Complete power-optimized stack, including controller and host

• GAP – central, peripheral, observer, or broadcaster (including combination roles)

• ATT / GATT – client and server

• SMP – AES-128 encryption and decryption

• L2CAP

• Sample applications and profiles

• Generic applications for GAP central and peripheral roles

• Proximity, accelerometer, simple keys, and battery GATT services

• More applications supported in BLE Software Stack

• Multiple configuration options

• Single-chip configuration, allowing applications to run on CC2541

• Network processor interface for applications running on an external microcontroller

• BTool – Windows PC application for evaluation, development, and test

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Current
Sensor

Gate

Driver

Device

Control

GND

EN

FB

VOUT

L

VREF

VIN

Device

Control

StartUp

VIN

VOUT

Block Diagram

2.1.3 TPS61220

• Up to 95% efficiency at typical operating conditions

• 5.5 μA quiescent current

• Startup into load at 0.7-V input voltage

• Operating input voltage from 0.7 V to 5.5 V

• Pass-through function during shutdown

• Minimum switching current 200 mA

• Protections:
– Output overvoltage
– Overtemperature
– Input undervoltage lockout

• Adjustable output voltage from 1.8 V to 6 V

• Fixed output voltage versions

• Small 6-pin SC-70 package

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Figure 4. TPS61220 Block Diagram

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V1

-

+

RLDINV

CMOUT

RLDOUT

DIGITAL

CONTROL AND

POWER

MANAGEMENT

Wilson

ref.

Digital

Filter

Σ∆

Modulator

Digital

Filter

Σ∆

Modulator

Digital

Filter

Σ∆

Modulator

-

+

-

+

InA

InA

InA

WCT

-

+

RA LA

LL

RL

IN1

IN2

IN3

IN4

IN5

IN6

R

1

R

2

C

1

I

II

V

SELRLD

WILSON_EN

CM

detect

CMDET_EN

-

+

RLD

Amp.

VSS

VDD

VDDIO

XTAL1

XTAL2

CVREF

5V

InA

CH1

CH2

CSB

SCLK

SDI

SDO

DRDYB

ALARMB

RLDIN

RLDREF

CH3

5V 5V

0.1 F

1

F

4.096
MHz

0.1 F

3.3V

0.1 F

22 pF 22 pF

CLK

VSSIO

SYNCB

1 MΩ

3.3V

REF for

CM & RLD

1 MΩ

RSTB

3.3V

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3 Theory of Operation

3.1 5-Lead ECG Application

Figure 5 shows the ADS1293 device in a 5-Lead ECG system setup. The ADS1293 device uses the

Common-Mode Detector to measure the common-mode of the patient’s body by averaging the voltage of
input pins IN1, IN2 and IN3, and uses this signal in the right leg drive feedback circuit.

NOTE: The ideal values of R1, R2and C1will vary per system/application; typical values for these

components are: R1= 100kΩ, R2= 1MΩ and C1= 1.5nF.

The output of the RLD amplifier is connected to the right leg electrode, which is IN4, to drive the common­mode of the patient’s body. The Wilson Central Terminal is generated by the ADS1293 and is used as a
reference to measure the chest electrode, V1. The chip uses an external 4.096MHz crystal oscillator
connected between the XTAL1 and XTAL2 pins to create the clock sources for the device.

Theory of Operation

CC2541 Communication

The CC2541 device communicates to the ADS1293 device through SPI interface. The CC2541 device
implements the application software to run this application through the 8051 microcontroller core in
addition to running the BLE stack. For additional information, see Section 4.4.

Figure 5. 5-Lead ECG Application

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Theory of Operation

3.2 Battery Life Calculation

For battery life calculations, TI highly recommends that the user reviews CC2541 Battery Life Calculation,

SWRA347.

Comparing the power consumption of a BLE device to another device using a single metric is impossible.
For example, a device gets rated by its peak current. While the peak current plays a part in the total power
consumption, a device running the BLE stack only consumes current at the peak level during
transmission. Even in very high throughput systems, a BLE device is transmitting for only a small
percentage of the total time that the device is connected (see Figure 6).

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Figure 6. Current Consumption

In addition to transmitting, there are other factors to consider when calculating battery life. A BLE device
can go through several other modes, such as receiving, sleeping, and waking up from sleep. Even if the
current consumption of a device in each different mode is known, there is not enough information to
determine the total power consumed by the device. Each layer of the BLE stack requires a certain amount
of processing to remain connected and to comply with the specifications of the protocol. The MCU takes
time to perform this processing, and during this time, current is consumed by the device. In addition, some
power might be consumed while the device switches between modes (see Figure 7). All of this must be
considered to get an accurate measurement of the total current consumed.

Figure 7. Current Consumption-Active versus Sleep Modes

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4 Getting Started

4.1 Software

Requirements:

• An iOS device: iPhone 4S and newer generations; iPad 3 and newer generations; fifth generation iPod
(www.Apple.com)

• 3.6-V Lithium-ion battery, recommended model BT-0001

• CC Debugger (http://www.ti.com/tool/cc-debugger)

4.1.1 Installing the Application

The application is not on iTunes (Apple Approved) for download. Download the application from the
following link: TIDA-00096 iOS Application Software .

Since the application is not on iTunes, use the steps below to install it manually. When the application is
distributed manually, there is a limit on how many devices can the application can be loaded on. The
UDID of each device needs to be provided before the application can be installed.

Use the following steps to install the Wireless Heart Rate Monitor application on a device.

1. Connect the iPhone or iPad to the PC.

2. Open the iTunes application on the PC.

3. Wait for iTunes to identify that the device is connected to the PC.

4. The serial number of the device is listed as shown in Figure 9.

Getting Started

Figure 8. 3.6-V Lithium-Ion Battery

5. In order to view the Identifier number (UDID), double click on Serial Number as shown in Figure 10

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Figure 9. Opening iTunes

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Getting Started

6. Report the identifier number (UDID) number to the iPad developer.

7. After the UDID is added to the application (by the iPad developer), a .zip file is sent to the iTunes user
that contains the application to download onto the smart device such as an iPhone4S®, iPhone 5®, or
iPad4®.

8. Unzip the folder to view the application, ecgmonitor.ipa.

9. Open iTunes

Once iTunes is open, use the following steps to install the application on the device.

1. Click the top-left button in the iTunes interface shown in Figure 11.

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Figure 10. Finding the UDID Number

2. Once the top-left button is clicked, a menu appears, click on Add File to Library (see Figure 12) to
navigate to and select the ecgmonitor.ipa file from the file directory.

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Wireless Heart Rate Monitor Reference Design TIDU195A–January 2014–Revised July 2014

Figure 11. iTunes library

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