maelli01 74 Posted April 21, 2017 Share Posted April 21, 2017 The example msp430fr5994x_lpm4-5_02.c is supposed to show how little current is used in this mode. In the file it says: // MSP430FR5x9x Demo - Entering and waking up from LPM4.5 via P1.3 interrupt // with SVS disabled // // Description: Download and run the program. When entered LPM4.5, no LEDs // should be on. Use a multimeter to measure current on JP1 and // compare to the datasheet. When a positive voltage is applied // to P1.3 the device should wake up from LPM4.5. This will enable // the LFXT oscillator and blink the LED (on P1.0). Even for a high-end multimeter this current is too low to be accurately measured. So I helped myself this way: - power the processor from the supercap - a 10k resistor with two antiparallel diodes act as a shunt, - connect the volt meter across the supercap, not across the processor 0.43mV over a 10k resistor gives 43 Nanoamps. (!) Yes, the datasheet (page 32) is right, typical value at 25°C is 45nA. A CR2032 (200mAh) cell would allow the processor to wait for an interrupt for 530 years. Fmilburn, veryalive, tripwire and 2 others 5 Quote Link to post Share on other sites
dubnet 238 Posted April 21, 2017 Share Posted April 21, 2017 Nice test. It would be interesting to see if running energy trace under CCS would yield a similar number. Quote Link to post Share on other sites
chicken 630 Posted April 23, 2017 Share Posted April 23, 2017 I guess the forward diode is to bypass the 10k resistor when the MCU draws more than 70uA. That's a great trick to remember. tripwire 1 Quote Link to post Share on other sites
maelli01 74 Posted April 24, 2017 Author Share Posted April 24, 2017 exactly, and the second diode to make it fool-proof chicken and tripwire 2 Quote Link to post Share on other sites
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