Kinetis KLx Low Power Modes with External 32kHz Crystal

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Kinetis KLx Low Power Modes with External 32kHz Crystal

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christhomas
Contributor II

I am using a KL16 and currently using the 4Mhz Internal Reference Clock. However, in order to reduce current consumption I would like to switch to my 32kHz crystal. 

Since 32 kHz is not fast enough for my calculations and timers, i need to enable the FLL. However, is it possible to use that mode in VLPR mode as again I want to minimise the current consumption as much as possible. Would that work in any of the low power modes or can I only run it in Normal Run Mode. 

In sleep modes (VLLS), is it more efficient to use the 32kHz crystal or the dedicated Low Power timer running off the LPO. 

Thanks! 

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Robin_Shen
NXP TechSupport
NXP TechSupport

Q1: is it possible to use that mode in VLPR mode as again I want to minimise the current consumption as much as possible.

A1: No. Only MCG modes BLPI and BLPE can be used in VLPR. You can find it in "Table 7-1. Chip power modes" of KL16P80M48SF4RM.

So if you want to use the external 32kHz crystal(BLPE), the frequency may not fast enough for your calculations and timers.

Table 7-1. Chip power modes.png

Q2: Would that work in any of the low power modes or can I only run it in Normal Run Mode. 

A2: If you want to use the FEE mode(external 32k crystal with FLL), you can only run it in  Normal Run Mode

Table 7-2. Module operation in low power modes.png

Q3: In sleep modes (VLLS), is it more efficient to use the 32kHz crystal or the dedicated Low Power timer running off the LPO.
A3: You can find the IEREFSTEN32KHz in "Table 10. Low power mode peripheral adders".

The LPO is always ON in VLLS1 and VLLS3, and can only be OFF in VLLS0 mode.

Table 10. Low power mode peripheral adders.png

Best Regards,

Robin

 

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