- General Design Guidelines
- Host MCU Recommendations
- Power Supply Selection
- Component Recommendations
- Notecard Electrical Characteristics
- Notecard Certifications
- MinSpin Design Support
- Ordering Information
- Terms & Conditions
- Contact Information
- Revision History
This application note covers how to design a low-power system that uses the Notecard for wireless communication. The Notecard is a family of system-on-module devices that can be used to add drop-in wireless connectivity for products.
Whether you are designing a product from scratch or adding the Notecard to an existing product to supply wireless connectivity, this document will help you navigate the design process and help you overcome some of the common challenges of designing a low power integration.
Notecard is designed to always be powered. Moreover, Notecard power architecture is designed so that it will gracefully enter and leave sleep states on its own or by software triggers (see Notecard API
card.aux). This has the advantage of reducing wear on the components from power cycling as well as keeping the modem ready at all times.
This application note focuses on low power; however, if you are new to Notecard, we strongly recommend you start with the Host System Design Guide for an overview of our recommendations.
As detailed in that guide, Notecard-based products should be designed with an M.2 Key E connector such as Amphenol MDT420E01001 and secured to a grounded standoff with mounting screw. Blues reference designs use a Würth Elektronik 9774025151R paired with an M2.5x4 metric machine screw.
In future Notecard designs, the M.2 mounting screw and standoff will stay in the same location; however, the Notecard's length may be extended by up to 7mm (from today's 35mm to 42mm) — to account for enhanced or additional components including, in some configurations, an RF antenna.
The hardware design files for every Notecarrier that Blues produces are open source and available in our GitHub hardware repository.
Notecarrier schematics contain our best practices around Notecard-based design, and we encourage you to consult these when integrating and building new products and are referenced throughout this document.
The Notecard can be configured to operate in five different modes: periodic, continuous, minimum, off, and DFU. These modes refer to the frequency of the cellular modem's activity. Periodic mode can be configured in software to communicate with Notehub at set intervals. This is ideal for low-power operation because every modem transmission expends joules.
Continuous mode like the name implies is a mode where the Notecard cellular modem does not stop transmitting. This mode is appropriate for certain customer applications.
To minimize power device power consumption, it’s important to understand the different modes of operation and how to set them with the Notecard API
Notecard can do dynamic line voltage detection or establish a USB Serial connection to Notecard, you must connect the
VUSB power pin and support the USB power design of Notecard.
For more see the Host System Design Guide.
The host microcontroller you select will affect your overall power consumption dramatically. While you can use almost any host microcontroller with Notecard, we have had good experience with the following MCUs for low power designs.
Regardless of which MCU you select, the overall integration with the Notecard will be relatively similar.
The STM32 from ST is a family of 32-bit microcontrollers based on the Arm Cortex-M with low power consumption and solid performance. The STM32L Series of MCUs pair nicely with low-power design due to the following key features:
- Ultra-low-power mode (ULPM): 8nA with backup registers without real-time clock (5 wakeup pins)
- ULPM + RTC: 200nA with backup registers (5 wakeup pins)
- ULPM + 8 Kbytes of RAM: 195nA
- ULPM + 8 Kb RAM + RTC: 340nA
For more technical information, see the STM32 microcontroller system memory boot mode application note.
The ESP32 from Espressif is another 32-bit MCU with a low-power sleep state which consumes less than 5μA. It also features onboard Wi-Fi and Bluetooth/Bluetooth LE, which may be appealing for certain product use-cases.
See the Espressif ESP32 Design Guide for their recommendations on working with the MCU.
Keep in mind that Notecard can be configured to power off or down the host MCU when not in use, the power consumption of the host MCU is not as hypercritical as the rest of the design.
This schematic shows a barebones design for integrating Notecard with your MCU of choice. It is important to note how Notecard interfaces with the host MCU and the power tree that must be provided for proper functionality.
In the schematic above, the power source is shown as a Scoop, which is an ideal way to provide power back-up to your product, but could just as easily be a Li-Po battery or line power that meets Notecard power supply requirements — the decision of which power source to use is very much use-case specific.
We recommend selecting and designing your power supply conservatively to accommodate all possible Notecard SKUs.
Cellular Notecards have specific power requirements to satisfy the power demands of the cellular radio. Your design must supply: 2V5 to 5V5 and be capable of a sustained 750mA draw and brief 2A bursts. This voltage must be applied to the
VMODEM_P pins of the M.2 connector (pins 70, 72, and 74).
Your power design must support for bursts of 2A to meet the requirements for GPRS/GSM communication. This is critical and must not be overlooked.
To power the Notecard MCU and its peripherals, you must supply a voltage of 1V8 or 3V3, capable of at least 150mA draw. We recommend designing for 500mA draw to allow for more headroom. This voltage must be applied to the
VIO_P pins of the M.2 connector (pins 2 and 4).
|Supply Voltage (V)||2V5||5V5|
|Supply Current (mA)||500mA||2A|
Keep in mind that a powered Notecard at idle consumes ~8µA at 3V3.
Notecard requires both 1V8 and 3V3 for proper operation. The Notecard block diagram below details the various level shifting you will need to provide to remain within tolerance of communication protocol voltage thresholds.
VMODEM (pins 70, 72, 74) operates at 2V5 ~ 5V5 whereas
VIO (pins 2 and 4) typically operates at either 1V8 or 3V3.
The Note-Wifi only takes 3v3 for VIO so if you want to make a product that works on cell and Wi-Fi you need to supply 3v3 or at least the provision for switching to 3v3 if you want to run cellular at 1v8 and be able to use Note-Wifi when necessary..
Because the operating voltages may differ, a logic shifter must be implemented; this doubles as protection between your Notecard and external peripherals — which is strongly suggested.
PMGD175XNE is a dual N-channel MOSFET used on the Notecard in conjunction with on-Notecard i2c devices for level shifting and isolation purposes.
The i2c Serial interface uses the
SCL_P (pin 40) and
SDA_P (pin 42) signals.
Notecard provides 10KΩ pull-ups on
SDA_P — no additional pull-ups are necessary.
You should provide appropriate termination resistance on
SDA_P. The Notecarrier reference designs use two 100Ω resistors for this purpose. For more information, please consult the Notecard Host System Design Guide.
For 1V8 we recommend the MAX17225 boost converter paired with a logic shifter such as the TXS0102DCUR or the NVT2002TLH. These parts have a low shut down current, high efficiency, and small quiescent current giving a broad feature set. The MAX17225 has a leakage current of only 0.1nA which is far superior to most others in the µA range.
We selected the MAX1722X because its job is to power the Notecard MCU, accelerometer and temp sensor, and the crypto engine. It has a very small quiescent current and has 95% peak efficiency. It also meets the 150mA spec in the block diagram above, plus a bit of overhead.
- 300nA Quiescent Supply Current Into OUT
- True Shutdown Mode
- 0.5nA Shutdown Current
- Output Disconnects from Input
- No Reverse Current with VOUT 0V to 5V
- 95% Peak Efficiency
- 400mV to 5.5V Input Range
- 0V88 Minimum Startup Voltage
- 1V8 to 5V Output Voltage Range
- Single 1% Resistor Selectable Output
- 1A output
Three specs to keep in mind while selecting a 1V8 level shifter are efficiency, shutdown current, and quiescent current. It is also important to keep protection and any kind of leakage current in mind when selecting your level shifter.
When selecting a power supply for your low-power design, it is critical to select a DC/DC with low quiescent current and high peak efficiency. The MAX1722X and ADP1606ACPZN1.8 appear like similar parts, and one may be cheaper, available, and easier to source than the other, but for the use-case of low-power design, the MAX1722X would be a better option.
- 23uA quiescent current
- True Shutdown Mode & Power Isolation
- 96% Peak Efficiency
- Fixed 1V8 output
- 1A output
The reason is because the MAX1722X mates perfectly with the power profile within Notecard that was specifically designed to cater to the health of cellular modem. In addition to that, our aim is for sub 1µA draw in shut down modes so the MAX1722X is eating up 0.3µA of that 1µA goal/budget whereas the seemingly similar part (ADP1606A) would take 23µA of that 1µA goal/budget.
Now that you are familiar with some of the low-power considerations in selecting components for level-shifting, the schematic from Notecarrier F's 3V3 level-shifting is provide for guidance.
To satisfy the Notecard's wireless modem power demands — especially at sudden intervals — a boost converter is used. The boost converter takes anything below the input voltage threshold and boost it so that it is within specification.
The specific power requirements for the modem will change based on the activity of the modem as well as if it is in a low-power sleep state. It is strongly suggested that you use one of the following boost converters for optimal low-power performance.
The table below is a list of similar DC/DC boost converters with fixed 1V8 output option and their listed iq for comparison.
|DC/DC Component||Typical iq||Description||Shutdown Current|
|MCP1640||0.7µA||0V8 to 5V5; 350mA||0.3µA|
|LTC3525||3µA||0V5 to 3V3; 400mA||0.5µA|
|TPS61236||5µA||0V5 to 1V8; 3A||0.01µA|
|TPS61220||5µA||0V7 to 5V5; 200mA||0.2µA|
|TPS61030||10µA||1V8 ~ 5V5 to 1V8; 3.6A||0.01µA|
|ADP1612||900µA||1V8 ~ 5V5 to 1V8; 1.4A||0.01µA|
It's helpful to use a table such as this when comparing efficiency and other specifications to meet your design requirements.
Power supply manufacturers will often-times have a product comparison matrix showing each of their part numbers and where they fit on a list such iq, maximum output current, maximum fixed output voltage, etc.
Below is a list of similar DC/DC boost converters with fixed 3V3 output option and their listed iq for comparison.
|Potential DC/DC Component||Typical iq||Description||Shutdown Current|
|TPS61021A||17µA||0V5 ~ 4V4 to 1V8; 3A||0.5µA|
|TPS61236||5µA||2V3 ~ 4V5 to 5V; 6.5A||0.01µA|
|MCP1640||19µA (PFM)||2V0 ~ 5V5 to 5V; 300mA||0.7µA (PFM)|
|TPS61220||5.5µA||0V7 ~ 5V5 to 1V8; 200mA||0.2µA|
This is a good starting point in comparing efficiency, availability, cost, and other specifications to ensure it will meet your design requirements.
The TPS6302x is a buck boost that caters to the unique requirements of the Notecard modem and the USB spec. The schematic from the Notecarrier F shows how to implement the TPS6302x in your design.
The Blues MinSpin Product Design Review Service is a complementary service offered to customers building Notecard and Notehub-based solutions. Customers can take advantage of this service to reduce implementation costs, product spins, and overall time-to-market.
As part of the service, customers will collaborate with blues technical support and applications engineers to define their product architecture, select key components, and ensure that their application is designed to utilize the best of what the Notecard and Notehub have to offer.
The service includes:
- Product architecture consulting
- A Product ideation session with blues product experts
- Schematic review
- PCB layout review
- Component placement consulting
- Component selection guidance for BOM cost optimization
For additional information about this service and to schedule an introductory conversation, please contact the Blues Team.
|David Scheltema & Tyler Wojciechowicz||14 SEP 2023||Initial Publication|