Hi,
I have to redo a remote because the transceiver has gone EOL and no pin to pin replacement is there.
New transceiver has been selected, this would also be a good time to change the MCU.
In this application the remote is in sleep for most of the time, and exchanges data with another gadget at the press of a button or in "active" modes.
there are three modes:
- Active connecting, 4 second sleep, 60ms active
- Active connected, 32 second sleep, 60ms active (this is the mode the remote will be the most. average current from the transceiver is 6.024/21.61 uA best/worst case scenarios)
- Idle, 256 second sleep, a couple of ms active just to occasionally check battery then go back to sleep
Pressing a button will put the remote in "Active connecting" mode
During activity current is dominated by the transceiver, but during sleep current is dominated by MCU.
Current MCU is a PIC16LF1823, chosen because i know it quite well... and it has a very low deep sleep current (in this case it is called "power down" in the datasheet, whereas for other families/brands with power down RAM power is removed, deep power down only way to exit is pulling a pin high/low)
I'll Assume i can trust the datasheet.
1823 has a Power down current + WDT (to exit from sleep) of 530 nA, says the datasheet (3.0V, 25°C). I can confirm it's in this ball park for all tested units during developement and production.
However, working with this chip is a pain in the butt, very little Flash/RAM.
Solution #1 is to scale up to 1824 or 1825 (increase flash/ram), make the code a little less hand optimized but more readable and call it a day.
Solution #2 is to choose a different MCU with low cost, low pin count (max 20 for TSSOP, max 32 for QFN) and a power down current in the same ballpark
What i've looked at for now:
From Microchip:
- Other PIC16: LF15325, LF18324. Basically, updated cores/peripherals. A bit more flexible, also for power managed modes but datasheet is still "Preliminary" with incomplete data. More than one year ago i rejected them for the same reason. sigh.
- only other family that had all the requirements (low cost, low pin count, low power down current, SPI and ADC) was the PIC32MM. this boasts 520nA typical power down current + WDT. Other plus would be easier programming
From NXP:
- LPC1111FDH20 has a very high deep sleep current, 6 uA. 220nA for deep power down and 4 always on registers (enough to save all the variables needed). Problem, with DPD only way to wake up the MCU is to pull the wake pin. The new transceiver doesn't have a low power oscillator and automatic wake up like the old one so i can't use this mode. pity.
- LPC822M101JHI33 is probably the only good candidate i found: seep power down with wake up timer, 1.1uA. Still very high, but apparently less variations across temperature range
And that's it. I didn't find anything else, that's a very short list. I accept suggestions
- I checked out some ATTiny or SAM parts but power down currents were way higher. Same for STM32 L0
- I'd avoid having to learn another family for this (8051, MSP, ..) unless i have better results
Suggestions?