4 years, 9 months ago.

LPC824 Power Consumption: A Check List

Hello, Our team struggled a bit with power consumption and we think we have narrowed down the major aspects. Here are a few findings. Please feel free to add more or correct my statements and I will take it from the comments and add it to this original post

1) Before going to deep-sleep, power-down make all pins DigitalOut and move them to low to reduce current consumption. Exceptions may apply. See below.

2) If you are using open drain pins and have hence pulled them high, keep them at 1 otherwise that will result in power consumption. SO DONT pull them low.

3) If you have pulled-high the reset pin to avoid any accidental resets of the MCU, keep them high. If you accidentally bring them low, this will consume power

4) If there are requirements where you have to keep certain pins high (to handle another module like bluetooth or wifi or gprs), make sure your design will accommodate the moving to "low" to ensure that it doesnt consume power

5) Reduce clock speed by importing mbed. My exp with mbed-dev shows there MAY be problems with sprintf.

6) Make sure you take the checklist and make ONE CHANGE AT TIME to easily theorize-identify-solve loop :)

7) If you are using a MCU package that has lesser # of pins than another in the same family, ensure that pins that are not in the smaller package (but are on the bigger package) are also pulled down. Take care of ALL pins in the MCU family

8) Evalutae turning Off BOD or WD to conserve power

Best regards Surendar

In general a good list, especially watch out you don't simply pull current through resistors. However regarding point 1: I have seen it advised often, yet I have never seen it make any difference. Granted I don't have the LPC824, but also for example the LPC812 it doesn't do anything. Does it really matter, or is it simply an urban legend that everyone keeps repeating?

posted by Erik - 08 Dec 2016


On #1, since my setup is intact, I have the capability to test. Let me try and get back to you shortly

posted by siva surendar 08 Dec 2016


Heres some info.

1) When we dont declare any pins then it donest comsume any power

2) When i declare a Pin for any other purpose then i have to change it to DigitalOut before gonig to sleep. Otherwise power consumption rises

So item #7 may not be right. Since, realistically, one will use a lot of pins applying #1 becomes improtant IMHO

posted by siva surendar 08 Dec 2016

Erik, If I am connecting a 3.3v from MCU to say a 3v circuit using a, say 4.7k resistance, because I dont want to use a level-shifting circuit (for space and simplicity sake), AND i am going to hold the pin high during deep-sleep or power down, then can I increase the resistance to say 10M to bring current to very small value?

In other terms, what is the limit of the resistance in these situations.?

posted by siva surendar 12 Dec 2016
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