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KL03: ADHSC=1 increases VLPS current from 2 uA to 85 uA

Question asked by Martin Krause on Mar 9, 2016
Latest reply on Mar 10, 2016 by Martin Krause

We have a KL03 board doing ADC measurements with internal ADCLK when the CPU is running. If nothing is to do we enter VLPS mode. Until now in VLPS mode we measured a MCU current of 2 uA. Now I set ADHSC bit to 1 to use the highest possible ADCLK. And surprisingly this increasese the current measured in VLPS from 2 uA to 85 uA??

 

Where does this heavy current increase come from? We do single ADC conversions, so the ADC (and thus the ADCLK) should be not running during VLPS (during VLPS we do not use/need ADC measurements). But if the ADCLK is not running during VLPS why is the MCU current increased if I set ADHSC to 1? If I configure ADHSC to 0 before entering VLPS, the current is 2 uA. So a possible workaround could be to set ADHSC to 0 before entering VLPS and set it back to 1 after the system woke up from VLPS. But I'm wondering why this is not documented somewhere in the datasheet / manual. Is this the expected/normal behavior, or am I doing something wrong?

If I have to swich ADHSC off to save power during VLPS, do I have to add some delay in my code before doing a ADC measurement after I set ADHSC to 1, to give the ADCLK time to switch to the higher frequency?

 

Best Regards,

Martin

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