I am doing a feasibility study for a product change to CapSense. The product spec calls for 1 uA sleep current. I see that the datasheet for one PSoC (CY8C20437) gives the following current numbers:
--1.1 uA for sleep
--0.1 uA for deep sleep
--28 uA "in run time" for scanning a single CapSense sensor
However, we all know that datasheets are.....well, let's say, "optimistic". In doing a little bit of playing around based on this article and this app note AN47310, I have gotten my power consumption down to ~200 uA (from 2 mA), during sleep mode, and a little more while scanning a single sensor. This is a far cry from the promised 1 uA, though.
What I've done so far - I took a basic 9-sensor in, 8-GPIO out, simple timer circuit and:
- Reduced clock speed IMO to 6 MHz and CPU_Clock to /4 -- this reduced my current from 2 to 1.5
- Implemented a basic sleep mode - down to 0.2 mA while sleeping
- Reduced the number of sensors scanned to 1
- Turned a couple of my outputs from Strong drive to Analog Hi-Z - this didn't seem to help power consumption
- I assume that the advice about turning analog off is inapplicable for CapSense
- Most of the other bullet points in the article are beyond my present knowledge of PSoC (analog column clock, VC clock dividers, etc. etc.)
So....my questions for the forum are:
- Is the quoted 1 uA range actually achievable? Has anyone done it? Is there low-hanging fruit I have missed?
- What about deep sleep mode? Will it actually go to 0.1 uA?
- Does anybody know of any further resources, examples, etc. than what I've found so far, to help with sleep / deep sleep / low power with CapSense?
N.b., I found this article, "Low and Battery power techniques with CapSense" which only refers to AN2360, "Capacitive Sensing - Power and Sleep Considerations", which is frustratingly AWOL. Maybe it was subsumed into the Design Guide or Getting Started, but they each only have about one page, with a small amount of useful information.
Also, there is AN47215, "PSoC RC Oscillator to Accurately Time Sleep Cycles", which I haven't gotten into yet because I don't need precise timing right now.
As mentioned, right now I am just trying to see if we can get within a microamp or three of 1 uA average sleep current, while maintaining one CapSense line to "wake up".
Thanks in advance,