Ultra-Low Power MCUs Minimize Current Consumption
How do chip makers differentiate if many ultra-low power MCUs on the market feature the same processor core? The peripherals and different power states offer various ways to manage current consumption down to microamps per megahertz.
What criteria do embedded developers and chip makers use to determine what makes a microcontroller qualify as an ultra-low-power device? For some MCU architectures, low power consumption is intrinsic by nature due to relatively small size, low-frequency cores, and minimal memory resources. The Arm Cortex-M4F core is one that comes to mind, and in this month’s Datasheet, the architecture is well represented among nine different selections.
The difference between a low-power and an ultra-low-power microcontroller SoC seems to lie within the peripherals around the cores and the schemes that they use to put the device in a deep sleep cycle when it is inactive. Scanning the differences between nine different ultra-low-power offerings offers insight into the key metrics that manufacturers want to instill with developers: microamps per megahertz (µA/MHz).
One of the datasheets profiled offers this metric: 0.20µA/MHz in VDD dynamic current sleep mode. The number itself seems impressive from a power-sipping perspective. But when you read the words after it, “dynamic current sleep mode,” questions arise about what exactly that means.
Do we have to program the device to reach that level, or does an embedded scheme figure that out through some smart current sensing apparatus? Does that apparatus carry some current consumption penalty? Of course, it all depends. Where will the device be used? Does it process intermittent sensor activity or deliver peak current from power up to power off?
When the processor core is the same across manufacturers, the competitive advantage comes from the peripherals surrounding the core and how it manages different states of operation when the device is at rest, how soon it needs to wake up, and how it delivers full power when needed.
If a processor core can be put to sleep, how will it know when to wake up to detect an event that it needs to record, process, and send a packet to the cloud? Various schemes are proposed, including one where the processor core stops spinning in a semi-inactive state. Still, the analog portion remains in a semi-awake state in case such an event triggers a sensor reading or alarm.
In these schemes, a processor can shift from deep sleep mode to fully active mode in milliseconds. It can also maintain memory power to ensure no data loss between cycles. In some datasheets presented below, cores can shuffle through as many as five power states before settling back down to “Deep Sleep.”
Still, other schemes to achieve ultra-low power rely on integrating components other than the MCU core on the premise that it is more efficient to perform a task on-chip than off the SoC die.
Industry’s Smallest Form Factor
Made for wearables, hearables and the like, Analog Devices’ MAX32660 boasts one ultra-low power number: 0.20μA/MHz in VDD dynamic current sleep mode. It gives users the maximum amount of operating time between battery charges, and the Arm Cortex-M4 32-bit microcontroller, 96KB SRAM and 256KB Flash memory are packed into a 1.6mm x 1.6mm, 16-bump WLP.
- Internal oscillator to 96MHz
- 256KB Flash memory
- 96KB SRAM in low power backup mode
- 16KB instruction cache
- Memory protection unit (MPU)
- Low 1.1V VCORE supply voltage
- 3.6V GPIO operating range
- Internal LDO
- -40°C to +105°C temperature range
- 85µA/MHz active executing from flash
- 2µA full memory retention power
- Backup mode at VDD = 1.8V
- 450nA ultra-low power RTC
- Internal 80kHz ring oscillator
- Optimal peripheral mix
- Platform scalability
- Up to 14 GPIO Pins
- Up to two SPI
- I2S
- Two UARTs
- Two high-speed I2C at 3.4Mbps
- Four-channel DMA controller
- Three 32-bit timers
- Watchdog timer
- CMOS-level 32.768kHz RTC output
- 4mm x 4mm, 20-pin TQFN-EP
- 3mm x 3mm, 24-pin TQFN-EP
- Sports watches
- IoT
Infineon PSoC 6
The Infineon PSoC 6 MCU is a high-performance, ultra-low-power and secure platform, purpose-built for IoT applications and based on the ARM Cortex-M4F. The CY8C61x4 product line offers digital programmable logic, high-performance analog-to-digital conversion and a rich set of analog peripherals that operate in device deep sleep mode for low-power analog signal processing. Ideal for battery-powered applications, low-power sensor processing, motor control, and more.
- 150MHz Arm Cortex-M4F
- Arm Cortex-M0+ reserved for system functions
- Ultra-low power 40nm platform
- Ultra-low power (0.9V) and low power (1.1V) core voltage operation
- 6 power management modes
- Active CPU current slope
- Cortex-M4: 40μA/MHz
- Cortex-M0+: 20μA/MHz
- Active CPU current slope with 0.9V core operation
- Cortex-M4: 22μA/MHz
- Cortex-M0+: 15μA/MHz
- Deep Sleep mode current of 7μA
- 64KB SRAM retention
- On-chip DC-DC Buck converter
Microchip PIC18-Q71
Microchip offers configurable, analog-focused MCUs for sensor interfacing designs with the PIC18-Q71 product family. Ultra-low-power operation achieved through Core Independent Peripherals (CIPs) and a high level of analog integration to simplify sensor interfacing and analog measurements, optimize system performance and reduce BOM cost. Made for LED lighting, predictive maintenance, medical, home automation, industrial process control, automotive and IoT.
- Operating Speed DC: 64MHz clock input
- Operating Range: – 1.8V to 5.5V
- -40°C to 85°C temperature range
- Low-Current Power-on Reset (POR)
- Configurable Power-up Timer (PWRT)
- Brown-out Reset (BOR)
- Up to 64KB of Program Flash Memory
- Up to 4KB of data SRAM Memory
- 256 Bytes data EEPROM
- Power-saving functionality
- Doze: Different cycle rates for CPU and Peripherals
- Idle: CPU halted, peripherals operate
- Sleep: Lowest power consumption
- Peripheral Module Disable (PMD)
- Selectively disable hardware
- Minimize active power consumption
- Analog peripheral manager
- Optimize power consumption
- Low-power mode features
- Sleep: < 1μA typical @ 3V
- 48μA @ 32kHz, 3V, typical operating current
AI-Colored Glasses
NXP is in pre-production with the i.MX RT700 that features up to five computing cores designed to power AI-enabled edge devices such as wearables, consumer medical, smart home, and HMI devices. Ultra-low power features come via “Sense Subsystem” that includes a second Arm Cortex-M33 and Cadence Tensilica HiFi 1 DSP, replacing an external sensor hub and reducing system design complexity, footprint, and BOM costs.
- Arm Cortex-M33 up to 325MHz
- HiFi 4 DSP up to 325MHz
- eIQ Neutron NPU up to 325MHz
- Sense Compute subsystem
- Arm Cortex-M33 up to 250MHz
- HiFi 1 DSP up to 250MHz
- 7.5MB on-chip SRAM
- Three xSPI interfaces
- Off-chip memory expansion
- Up to 16b-wide external memories
- Up to 250MHz DDR
- Two SD/eMMC memory card interfaces
- eMMC 5.0 with HS400/DDR operation
- USB high-speed host/device controller
- Eight-channel microphone interface
- Serial peripherals (UART/I²C/I3C/SPI/HSPI/SAI)
- 2.5D GPU with vector graphics acceleration
- SIMD/DSP instructions
- Up to 720p@60FPS
- CSI 8/10/16-bit parallel (via FlexIO)
- EdgeLock Secure Enclave
- Secure boot and debug
- Crypto-TRNG, DICE, UID, PUF, OTP
- Crypto accelerators for PKC, AES, SHA
- Tamper and intrusion detection
Qorvo Motor Control
The Qorvo PAC55710 is a 70V BLDC motor controller and driver that offers Vds Sensing, Cycle By Cycle (CBC), Enhanced Sample And Hold (S&H), Windowed Watchdog Timer for controlling and powering smart energy appliances, devices, and equipment. The SoC integrates a 150MHz Arm Cortex-M4F 32-bit microcontroller core with Qorvo’s proprietary and patent-pending Multi-Mode Power Manager, configurable analog front end, and application specific power drivers.
- 150MHz Arm Cortex M4F
- 128kB Flash
- 32kB SRAM
- 70V Buck/SEPIC DC/DC Controller
- 5V/200mA system supply
- 3 High-side 70V 1.2A (source)/1.8A (sink) gate drivers
- 3 Low-side 20V 1.2A (source)/1.8A (sink) gate drivers
- Vds Sensing
- Advanced Cycle-by-Cycle Protection
- 3 Differential PGA (x1 to x48)
- 4 Single PGA (x1 to x48)
- Programmable over-current shut-down
- High-speed 12-bit 2.5MSPS ADC
- with dual auto-sampling sequencers
- 3.3V I/Os,
- Simultaneous sample and hold for three-phase
- 5.2V to 70V input voltage range
- UART/SPI, I2C, and CAN serial interfaces
- 25x MCU GPIOs
- 48-pin TQFN package, 6mm x 6mm
Ultra-Low Renesas
The Renesas RA0E1 offers ultra-low power consumption, up to 32MHz of CPU performance with an Arm Cortex-M23 core, 64KB flash, 12KB SRAM and a wide supply voltage range from 1.6V to 5.5V. The RA0 devices consume only 84.3μA/MHz of current in active mode and only 0.82mA in sleep mode. Designed for low-power consumer electronics, small appliance system control, industrial system control, and building automation.
- 32MHz Arm Cortex-M23 core
- 64KB Flash
- 12KB SRAM
- 1KB data flash memory
- 16-pin and 32-pin package options
- 1.6V to 5.5V voltage range
- TAU 16-bit general PWM timer
- TML32 32-bit interval timers
- RTC
- 12-bit A/D converter
- Temperature sensor
- SAU (UART, Simple SPI, Simple I2C)
- UART
- Random number generator
- Flash area protection
- Illegal memory access detection
- ±1% high accuracy oscillator
- Flexible power architecture
- System power management
- Low power modes
- Low Voltage Detection (LVD)
- Fast wake-up
- -40°C to +105°C temperature range
- 16-pin HWQFN (3 mm × 3 mm, 0.5 mm pitch)
- 32-pin LQFP (7 mm × 7 mm, 0.8 mm pitch)
Power So Low, It’s Silly
The Silicon Labs series of EFM32PG23 Gecko MCUs is intended for energy-friendly embedded applications. The ultra-low power package has an 80MHz Cortex-M33 with analog and communication peripherals and a low 21μA/MHz in Active Mode for in metering, industrial automation, test and measurement, appliance, and portable medical device applications.
- 32-bit 80MHz ARM Cortex-M33
- DSP instruction and FPU
- Up to 512kB flash program memory
- Up to 64kB RAM data memory
- Low Energy Consumption
- 21μA/MHz in Active Mode at 80MHz
- 1.33μA EM2 DeepSleep current
- 64KB RAM retention and RTC
- 1.03μA EM2 DeepSleep current
- 16KB RAM retention and RTC
- 1.71V to 3.8V operating range
- -40°C to 125°C
- QFN40 5mm × 5 mm × 0.85 mm
- QFN48 6mm × 6mm × 0.85mm
- High speed mode up to 2Msps
- High accuracy mode up to 16-bits ENOB at 3.8ksps
- 2 Analog comparators (ACMP)
- Two-Channel Digital-to-Analog Converter (VDAC)
- Low-Energy Sensor Interface (LESENSE)
- Up to 34 General Purpose I/O pins
- 3 EUSART
- UART/SPI/Smart Card
- 2 I2C interface with SMBus support
- HW cryptographic acceleration
- TRNG
- 34 GPIO pins
Alarmingly Low Power
The STM32L0 series is STMicroelectronics’ entry-level range of 32-bit MCUs designed for ultra-low power consumption levels as low as 49µA/MHz with external DC/DC. With dynamic voltage scaling, the STM32L051x6 with an Arm-based Cortex-M0+, with 64KB Flash, 8KB SRAM, 2KB EEPROM, and an ADC is aimed at energy harvesting, smoke detectors, gas and water meters and consumer devices with advanced battery management and fast charging.
- Ultra-low-power platform
- 1.65V to 3.6V power supply
- -40°C to 125 °C temperature range
- 0.27µA Standby mode (2 wakeup pins)
- 0.4µA Stop mode (16 wakeup lines)
- 0.8µA Stop mode + RTC + 8-Kbyte RAM
- retention
- 88µA/MHz in Run mode
- 3.5µs wakeup time (from RAM)
- 5µs wakeup time (from Flash)
- 340nA ULP mode/full RAM/lp timer
- Arm 32-bit Cortex-M0+ with MPU
- 32kHz up to 32MHz maximum
- 0.95 DMIPS/MHz
- 64KB Flash memory
- 8KB RAM
- 2KB of data EEPROM
- 51 fast I/Os
- 45 I/Os 5V tolerant
- Ultra-safe, low-power BOR
- Ultra-low-power POR/PDR
- 1MHz to 25MHz crystal oscillator
- 32kHz oscillator for RTC
- 12-bit ADC 1.14Msps up to 16 channels (down to 1.65V)
64-Bit Display Play
Power-optimized and efficient for display and graphics applications, the Texas Instruments AM62x brings up to four 64-bit Arm Cortex-A53s. The jump up from a 32-bit architecture doesn’t necessarily mean exorbitant power consumption—rather it enables dynamic control of system resources with finer granularity. The AM62x is certified for automotive systems where power demands are many and supply is finite.
- Quad-core Cortex-A53 cluster
- 512KB L2 shared cache
- With SECDED ECC
- 32KB L1 DCache per A53 Core
- Dedicated device power manager
- Partial I/O support for CAN/GPIO/UART wakeup
- DeepSleep
- MCU Only
- Standby
- Dynamic frequency scaling for Cortex-A53
- Dual display support
- 1920×1080 @ 60fps for each display
- 1x 2048×1080 + 1x 1280×720
- OLDI (4 lanes LVDS – 2x)
- 3D Graphics Processing Unit
- Fillrate greater than 500Mpixels/sec
- >500MTexels/sec, >8 GFLOPs
- 60fps
- One Camera Serial interface (CSI-Rx)
- MIPI CSI-2 v1.3 Compliant + MIPI D-PHY 1.2
- Arm Cortex-M4F MCU at up to 400MHz
- 16nm technology
- 13mm x 13mm, 0.5mm pitch FCCSP
Datasheet URLs:
Analog Devices: https://www.analog.com/media/en/technical-documentation/data-sheets/max32660.pdf
Infineon: www.infineon.com/dgdl/Infineon-PSoC_6_MCU_CY8C61X4-DataSheet-v06_00-EN.pdf?fileId=8ac78c8c7ddc01d7017ddd0276175906
Microchip: https://ww1.microchip.com/downloads/aemDocuments/documents/MCU08/ProductDocuments/DataSheets/PIC18F26-46-56Q71-Microcontroller-Data-Sheet-DS40002329.pdf
NXP: https://www.nxp.com/products/i.MX-RT700?tid=vanimxrt700
Qorvo: https://www.qorvo.com/products/d/da009499
Renesas: https://www.renesas.com/en/document/dst/ra0e1-group-datasheet
Silicon Labs: https://www.silabs.com/documents/public/data-sheets/efm32pg23-datasheet.pdf
STMicroelectronics: https://www.st.com/resource/en/datasheet/stm32l051c6.pdf
Texas Instruments: https://www.ti.com/lit/ds/symlink/am625.pdf?ts=1732405727003&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FAM625
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JANUARY 2024 #414 – Get a PDF of the issue
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Tom Murphy has been plying his trade as a technology journalist for more than 25 years, first as an editor/writer/reporter and then as a communications professional. He has earned industry recognition for both journalistic endeavors and technology campaigns. Before joining Circuit Cellar magazine as editor-in-chief (2024), Tom wrote tech briefs, newsletters, blogs, press releases, white papers, and technical articles for numerous clients, primarily in the semiconductor industry. His introduction into the industry came as an editor for “Electronic News” covering microprocessor companies, the fabless semiconductor phenomena, communication chips, and many others. When he’s not tapping away at the keyboard, Tom learns Dungeons and Dragons terminology from his 10-year-old daughter and walks his bulldog (slowly) around the block.
