Description
This reference design is an IEC60601-1-8 compliant medical alarm system utilizing the MSPM0G1507 or MSPM0G3507 microcontroller (MCU) to offer primary alarm, backup alarm, and visual alarm functionality. The MCU reads audio from internal or external flash and outputs the digital-to-analog converter (DAC) waveform to the audio amplifier. During system power loss, the backup piezo buzzer and MCU with integrated real time clock (RTC) remain powered from a supercapacitor.
Resources
- TIDA-010264: Design Folder
- MSPM0G1507: Product Folder
- MSPM0G3507: Product Folder
- TPS61094: Product Folder
- TPA6211A1: Product Folder
Contact TI E2E™ support experts for assistance.
Features
- IEC60601-1-8 compliant primary, backup, and visual alarm system
- Capability to play standard and custom alarms with 128kB internal flash and external flash options
- 12-bit, adjustable frequency (capable of 48 kHz+) high-fidelity audio using integrated DAC
- Over 3 minute backup alarm using supercapacitor backup
- 3 visual alarm LEDs: high, medium, and low priorities
- 49-mm diameter - small form factor for space-constrained medical applications
Applications
- Infusion pump
- Multiparameter patient monitor
- Ventilators
- Dialysis machine
- Anesthesia delivery systems
System Overview
System Description
Medical alarm systems are a required subsystem for most medical devices, especially those used in an intensive care unit (ICU). For patient safety, these medical devices must comply with the requirements established by the International Electrotechnical Commission (IEC). The IEC60601-1-8 standard details the necessary alarm-related elements for these systems including a primary alarm, a redundantly powered backup alarm, and a visual alarm indicator. This design provides an IEC60601-1-8 medical alarm utilizing the MSPM0G1507 microcontroller (MCU) to offer primary alarm, backup alarm, and visual alarm functionality. Figure 2-1 depicts the design block diagram.
Block Diagram
The system block diagram illustrates the integration of key components. A microphone feeds into an MCU (MSPM0G150x) which processes audio signals for primary alarm output via an audio amplifier (TPA6211A1) connected to a speaker. Visual alarm functionality is provided by LEDs. A backup alarm system, featuring a piezo buzzer, is powered by a supercapacitor. This supercapacitor is managed and charged by a bidirectional buck/boost converter (TPS61094). The MCU also interfaces with external flash memory for audio storage. The backup alarm is triggered by various inputs, including a watchdog timer (TPL5010) and logic gates, and can be overridden by the MCU. The diagram shows connections for external flash, microphone, primary alarm output (speaker), visual alarm LEDs, backup alarm (piezo buzzer), supercapacitor, and power inputs.
Design Considerations
Primary Alarm Circuit - Current Sensing
The primary alarm circuit uses the TPA6211A1 class AB audio amplifier. Low-side current sensing is implemented using a 20-mΩ shunt resistance (R20). This resistance is voltage-amplified by the MSPM0 MCU's internal op-amp with a gain of 32, and then digitized by a 12-bit ADC. This measurement helps detect speaker connection and monitor current. During testing with a 4-Ω speaker and 3.3-V input, a maximum current of approximately 0.6 A was measured in a high-alarm state. The following equations define the relationship between shunt resistance, current, and ADC steps:
Vshunt = Rshunt × Ishunt
VADC = 32 × (Rshunt × Ishunt)
With Rshunt = 20 mΩ and I_shunt_max = 0.6 A, the maximum VADC is 0.384 V.
Max # ADC Steps = (VADC max / VREF) × 4095
With VREF = 3.3 V, the maximum ADC steps are 496.
Microphone Circuit - Coincidence Detection
An optional microphone circuit is included for environmental feedback, such as ambient noise or acoustic feedback from the primary alarm. This circuit connects to the MSPM0's op-amp for signal conditioning.
Backup Alarm Circuit
The backup alarm circuit triggers the backup alarm if primary power is lost or if the MCU initiates the alarm. An external watchdog timer (TPL5010) resets the MCU if the system becomes unresponsive. The backup alarm can be disabled by the MCU via a secondary alarm override signal, allowing the MCU full control for specific durations (e.g., 3 minutes).
Supercapacitor Charging Circuit
This circuit manages supercapacitor charging and provides backup power. The TPS61094 is used as a bidirectional buck/boost converter. It charges the supercapacitor and provides regulated output voltage from the supercapacitor when primary power is lost. The charging voltage (VCHG) is set to 2.7 V, and charging current (ICHG) to 250 mA. A minimum voltage of 0.7 V is required for supercapacitor operation.
Equation 2 shows usable energy storage for supercapacitors rated below 5 V:
EJoules = ½ × C × V² - ½ × C × (0.7V)² {Supercapacitor VCHG < 5 V}
Simplified: EJoules = ½ × C × V² - 0.245 × C {Supercapacitor VCHG < 5 V}
For a 2.7 V, 5 F supercapacitor, this design offers 17 joules of energy storage. Equation 3 shows usable energy storage for supercapacitors rated 5 V or greater:
EJoules = ½ × C × (5V)² – 0.245 × C {Supercapacitor VCHG ≥ 5 V}
Simplified: EJoules = 12.255 × C {Supercapacitor VCHG ≥ 5 V}
Operation Modes
| MODES | EN | MODE | BYPASS | BOOST | BUCK | FUNCTION |
|---|---|---|---|---|---|---|
| Forced bypass | 0 | 0 | ✔️ | ❌ | ❌ | Turn on bypass MOSFET, turn off boost or buck, VOUT = VIN |
| True shutdown | 0 | 1 | ❌ | ❌ | ❌ | Bypass disconnect, turn off boost or buck, VOUT = 0 V |
| Forced buck | 1 | 0 | ✔️ | ❌ | ✔️ | Buck enabled, turn on bypass MOSFET, VOUT = VIN while charging the supercapacitor or backup battery |
| Auto buck or boost | 1 | 1 | ✔️ | ❌ | ✔️ | Buck enable, when VIN > target VOUT +100 mV and VOUT > target VOUT, supercapacitor is charged by buck |
| Auto buck or boost | 1 | 1 | ✔️ | ✔️ | ❌ | Boost and bypass enabled; when VOUT + 100 mV > VIN > target VOUT and VOUT = target VOUT, VOUT is from both VIN through bypass and supercap by boost. |
| Auto buck or boost | 1 | 1 | ❌ | ✔️ | ❌ | Boost enable; when VIN < target VOUT, VOUT is powered from supercapacitor by boost. |
Software Flow Chart
The software flow chart outlines the device's operation. It begins with device initialization, followed by declaration of audio data and alarm timings. The system then configures the DAC, volume, and alarm state. An interrupt service routine (ISR) for the DAC is triggered by a timer interrupt. The system enters a selected alarm state playback loop, outputting DAC values. The process repeats until the pulse playback is complete, after which a delay occurs between alarm pulses. The loop continues until the alarm is no longer active.
Highlighted Products
MSPM0G150x
The MSPM0G150x is a highly-integrated, ultra-low-power 32-bit MCU based on the Arm Cortex-M0+ core, operating up to 80-MHz. It offers high-performance analog peripherals, extended temperature range (-40°C to 125°C), and supports supply voltages from 1.62 V to 3.6 V. Key features include up to 128KB flash memory with ECC, 32KB SRAM, a memory protection unit, DMA, math accelerator, multiple ADCs, DACs, comparators, op-amps, timers, watchdog timers, and communication interfaces (UART, I2C, SPI). The MSPM0 family provides a holistic ultra-low-power system architecture.
TPS61094
The TPS61094 is a 60-nA IQ boost converter with supercapacitor management, suitable for smart meter and supercapacitor backup power applications. It supports a wide input voltage range and output voltage up to 5.5 V. It operates in buck mode for supercapacitor charging and boost mode to regulate output voltage from the supercapacitor when primary power fails. It features low quiescent current (60-nA in boost mode) and supports true shutdown and forced bypass modes.
TPA6211A1
The TPA6211A1 is a 3.1-W mono fully-differential amplifier designed to drive a speaker with at least 3-Ω impedance. It operates from 2.5 V to 5.5 V and draws only 4 mA of quiescent supply current. It is available in space-saving packages and offers features like high supply voltage rejection, improved RF immunity, and fast startup with minimal pop, making it suitable for various portable applications.
Hardware, Software, Testing Requirements, and Test Results
Hardware Requirements
| EQUIPMENT | RATING | DESCRIPTION |
|---|---|---|
| DC Power Supply | 3.3 V, 1 A | Device input power |
| Speaker | 4 Ω | Primary Alarm Sound Output |
| SPI Flash Programmer | - | For programming custom audio to SPI flash |
| MSPM0 Programmer | - | Any MSPM0 LaunchPad™ or XDS110 debug programmer |
Software Requirements
Programming MSPM0 MCU
To program the MCU, connect the MSPM0 programmer's GND, NRST, SWDIO, and SWCLK pins to the J3 connector. Connect an external 3.3-V DC power supply to the VIN and GND connections on the alarm board. Program the MCU using the Code Composer Studio™ integrated development environment (IDE) on a host computer.
Programming External SPI Flash
An SPI flash programmer is required to write audio to the external flash. Connect the programmer to the J2 connector. Ensure the SPI programmer operates at 3.3 V before flashing the audio.
Test Setup
| CONNECTOR | DESCRIPTION |
|---|---|
| VIN, GND | Connected to DC power supply, 3.3 V |
| SPK+, SPK- | Connected to 4-Ω speaker |
| SPI Flash Programmer | Connected to J2 |
| MSPM0 Programmer | Connected to J3 |
Test Results
Primary Alarm Waveforms
Figure 3-1 shows the measured waveform at the output of the MSPM0 12-bit DAC during a high-alarm state, illustrating pulsed audio output. Figure 3-2 displays the corresponding speaker output waveform, representing the amplified alarm sound.
Custom Audio Waveform
Figure 3-3 presents an example custom audio waveform measured from the speaker terminals.
Primary Alarm Harmonic Testing
Figure 3-4 shows the harmonic content of the high alarm state. The IEC60601-1-8 requirements mandate that at least four harmonics must be within +/- 15 dB of the fundamental frequency's amplitude. This test confirmed that eight harmonics fall within this required range for the high alarm state.
Coincidence Detection
Figure 3-5 shows the high-alarm state current-sense waveform, indicating current consumption through the speaker. A significant reduction in current suggests a speaker fault (e.g., disconnection). Figure 3-6 displays the analog signal output from the microphones during a high alarm state, capturing both the alarm sound and ambient noise levels, which can be used for volume adjustment.
Backup Power Transition
Figure 3-7 illustrates the transition from external 3.3-V power to the 3-V supercapacitor backup source, showing the voltage change and switchover. Figure 3-8 depicts the reverse transition, from the supercapacitor backup mode back to the external 3.3-V power source.
Alarm Sound Levels and Backup Alarm Runtime
| ALARM TYPE | SOUND LEVEL (dBA AT 1 m) | RUNTIME |
|---|---|---|
| Primary | 73.3 | Continuous (line power) |
| Backup (0-Ω series resistance) | 68.8 | 2 minutes 50 seconds from 2.7-V, 5F supercapacitor |
| Backup (43-Ω series resistance) | 66.3 | 3 minutes 52 seconds from 2.7-V, 5F supercapacitor |
Design and Documentation Support
Design Files
Schematics and Bill of Materials (BOM) can be downloaded from the design files at TIDA-010264.
Tools and Software
Tools
Code Composer Studio™: An integrated development environment (IDE) for TI microcontrollers and processors, offering tools for developing and debugging embedded applications. Available for Windows, Linux, and macOS, and also in the cloud via the TI Developer Zone.
Software
TIDA-010264-MSPM0G150x-FW: Downloadable firmware for the onboard MSPM0G150x, enabling an IEC60601-1-8 compliant medical alarm design with standard and custom audio playback.
Documentation Support
Additional documentation includes:
- Texas Instruments, MSPM0-Based Medical Alarm Design application brief
- Texas Instruments, Hardware-Based Smart DAC Medical Alarm Design application brief
- Texas Instruments, Demystifying Medical Alarm Designs With Smart DACs application brief
- Texas Instruments, Demystifying medical alarm designs, part 1: IEC60601-1-8 standard requirements TI E2E™ forum
- Texas Instruments, Demystifying medical alarm design, part 2: Design inputs and existing techniques TI E2E™ forum
- Texas Instruments, TPS61094 60-nA Quiescent Current Boost Converter With Supercap Management data sheet
- Texas Instruments, MSPM0G150x Mixed-Signal Microcontrollers data sheet
- Texas Instruments, TPA6211A1 3.1-W Mono Fully Differential Audio Power Amplifier data sheet
- Texas Instruments, TPL5010 Nano-Power System Timer With Watchdog Function data sheet
Support Resources
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