MK20 to MK22 migration

[pulsatrixp1]

Hello, 

I have a design in an MK20 microcontroller and will migrate to MK22. (MK22FN1M0AVMC12). I cannot seem to find reference wiring diagrams / designs for this device. 

Are the minimum required connections the same as the MK20? 

Where can I find a complete wiring diagram for that specific device?

Thank you in advance

[pulsatrixp1]

Hi Kerry,

Thank you for your reply. The part number I am using in the current design is MK20DX256VLH7 and I am basically following the connections from the teensy 3.1 schematic from Teensy and Teensy++ Schematic Diagrams  , without using the MINI54TAN, since I am programming directly with a Multilink USB programmer.

I will have a look to the TWR tower system design and base my design on its basic connections, if this is a more appropriate configuration for the  MK22FN1M0AVMC12.

Thank you again for your support.

[kerryzhou]

Hi Pulsatrix P1,

   The schematic for TWR-K21F120M can be downloaded from this link:

http://www.nxp.com/assets/downloads/data/en/printed-circuit-boards/TWR-K21F120MA-PWB.zip 

  This schematic is using MK21FN1M0AVMC12, your MK22FN1M0AVMC12 totally can use this schematic.

Wish it helps you!

Have a great day,
Kerry

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[pulsatrixp1]

Hi Kerry,

I have been working based on the design of the TWR schematic indicated and it has been helpful. Now I am looking at the connections for the pin RTC_WAKEUP, which in the case of the MK21 is RTC_WAKEUP and in the MK22 is RTC_WAKEUP_B. I read in this application note http://cache.freescale.com/files/32bit/doc/app_note/AN4503.pdf  that this RTC_WAKEUP_B can be used to switch the main power of the uC and leave only the VBAT, but not more details are given and the TWR schematic does not show this functionaliti, which sounds something that would really benefit my application in terms of power consumption. 

Based on what is described there I would guess that one could connect both VBAT and VDD to a regulated 3.3V source, but VDD would be connected through a transistor / switch that would be managed from the RTC_WAKEUP_B am I correct? Is there any application note or schematic that shows a tested version of this functionality and that I could implement?

An additional question: I see that the capacitors for the 32.768 KHz crystal as indicated as Do not Place (DNP). Should I still place them in my custom board, should I leave the places just in case they are needed, or can I directly ignore them? It is worth mentioning that the least components I need the better, since space is limited in my case.

Thank you in advance.

Best Regards,

Ivan

[kerryzhou]

Hi Pulsatrix P1,

1. RTC_WAKEUP_B

The absolute lowest power mode is "powered VDD OFF". This mode uses the RTC_WAKEUP to control the MCU VDD. On some later Kinetis devices with isolated VBAT power domains, like the K22F, K64, K24 and K65, there is a control output called RTC_WAKEUP_B that can be used to gate on the MCU VDD using an external component.

If you want to use this mode, you need to connect VBAT to the battery, then in the low power mode, the mode is powered from the battery, the VDD you can connect to a external component, which can be controlled by the RTC_WAKUP_B, when the mcu is waked up, then RTC_WAKUP_B is assert(ative low, open drain), to control the external component ouput the 3.3v to VDD. You can use the switch.

About the schematic, we don't directly have it, but it is not difficult to add the external component.

2. the capacitors for the 32.768 KHz crystal 

There are two programmable capacitors with this oscillator, which can be used as the Cload of the oscillator. The programmable range is from 0pF to 30pF.

You can refer to the schematic to use :

XTAL 32.768KHZ PAR 20PPM -- SMT

Wish it helps you!

Have a great day,

Kerry

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[pulsatrixp1]

Hi Kerry,

Thank you for your reply.

In my application the board will be running from a 3.7 V battery which is regulated to 3.3V. If I understand correctly then I can use the 3.3V for both VDD and VBAT but VDD will go through the switch and will be only used when RTC_WAKEUP_B activates it, is this correct? If so, which is the default state of RTC_WAKEUP_B? Is it normally low until I configure the module to periodically activate/deactivate VDD?

Thanks,

Best Regards,

Ivan

[kerryzhou]

Hi Pulsatrix P1,

From the reference manual:

The RTC wakeup pin is an open drain, active low, output that allows the RTC to wakeup the chip via an external component. The wakeup pin asserts when the wakeup pin enable is set and either the RTC interrupt is asserted or the wakeup pin is turned on via a register bit.

Open drain pin, you need to add external 4.7K to 10K external pull up resistor, then the default state is high, if the RTC interrupt asserts or the wakeup pin is turned on. Wakeup pin asserts (active low, open drain) ,

Have a great day,
Kerry

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[kerryzhou]

Hi Pulsarix P1,

    What the part number of your K20 chip?

   In K20 series, there have a lot of part numbers. Different part number have different character, especially when the max core frequent is different.

  About the MK22FN1M0AVMC12 design, you can refer to the TWR-K21F120M,  you can find it from this link:

TWR-K21F120MA|Tower System Board|Kinetis MCUs|NXP 

 Wish it helps you.
Have a great day,
Kerry

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