Norwegian microcontroller firm Energy Micro has released further details of its ARM Cortex M3-based EFM32G range, claimed to be the most energy efficient MPUs available.
"We are comparing with the best of 8, 16 and 32bit microcontrollers," said CEO Geir Forre.
Measured on silicon and not just modelled, said Forre, in 'run mode' current consumption is under 180µA/MHz while executing real code from flash; stand-by consumption is typically 900nA with real-time clock, power-on reset, and brown-out detector running, and RAM data and CPU state retained; and in deepest sleep, quiescent is less than 20nA.
The firm is using TSMC's ULP (ultra-low power) 180nm CMOS process for lowest current drain as finer geometry processes are still too leaky. This sets minimum operation voltage at 1.8V.
"We would love to be at 0.9V, but it is not possible," said Forre. "We will not go to 130nm because there is no flash. The next node is 90nm and we can go there if spin-offs from 32 and 22nm development cut stand-by."
The company has gone to great lengths to cut circuit consumption and remains tight-lipped about much of its technology, but Forre revealed some measures that have been taken to increase battery life:
"The on-chip regulator needs a decoupling capacitor," he said. "If you shut-down and turn-on, it needs to discharge and charge. We are taking it away - we disconnect it in deep sleep so it is charged when we wake up."
He also said that the inevitable bandgap voltage reference is only on for a short time rather than continuously. "We are doing clever things with it, and are filing a patent."
Efforts have been made to reduce unproductive time during mode-switches.
Wake-up is 2µs with clocks running (900nA sleep), or 10µs from complete shut-down with no clocks running.
Just about all of the peripherals are capable of autonomous operation, so once the programme has set-up a transaction between peripherals, or between peripheral and memory, the core can be shut down.
"There are a lot of activators that can trigger consumers in a programmable way," said Forre. "For example, you can set up your timer to do an ADC conversion at a certain period, or a voltage comparator can trigger a timer to measure a pulse width."
Forre is claiming exceptionally high power efficiency amongst the peripherals. "The 4x40 segment LCD controller is a peripheral we are extremely proud about," he said. "I haven't seen any stand-alone driver than is better. The best we know about is watch chips at 1.5µA. Ours is 900nA from 3V."
For LCD operation from depleted alkaline cells (2.2V), an integrated boost converter can be switched on.
The on-chip eight-channel ADC consumes 200µA in 12bit mode at 1Msample/s, dropping to 500nA for 6bit 1ksample/s operation.
Alongside a standard UART and USART there is a low-energy UART with a 32kHz clock that consumes 100nA at 9,600baud.
"It can be used to communicate with an RF transceiver," said Forre. "We wonder why no one else thought of a low-energy UART. The idea came from input from one of our customers."
Other peripheral highlights are a 50nA 32kHz real time counter, a 100nA brown-out detector, and a 1°C accurate temperature sensor.
There are five modes to chose from: 180µA/MHz run, 45µA/MHz sleep (where peripherals can communicate), 900nA deep sleep (RAM retained, brown-out detection enabled, and clocks on for fast wake), 600nA stop (power-on-reset enabled and memory retained) and 20nA shutoff with only pin reset and power-on reset enabled.
If self-discharge was not a factor, the company is claiming over 20 years of operation would be possible from a CR2032 lithium coin cell running an application that required the core to operate every 40ms on a 0.5% duty cycle.
Operation is between 1.8 and 3.8V, and from -40 to 85°C.
22 parts are being released between the first of December and March next year, in QFN32, QFN64, QFP100 and BGA112 packages.
Memory ranges up to 128kbyte of flash and up to 16kbyte of RAM.
Initial 32pin devices start at $1.55 in 100k quantities.
