topic Re: K02 DAC output logic level during Power-On Reset (POR) in Kinetis Microcontrollers

K02 DAC output logic level during Power-On Reset (POR)

marielu — Wed, 30 Sep 2015 03:10:31 GMT

Dear Sir or Madam,

I'm using the K02FN64VFM10, and would like to use the DAC port to generate a slope signal. Processor Expert is used to initialize the DAC module.

During the power-on process, the DAC output stays at 3 V for about 250 ms, and then drops to 0 V and start to generate the slope signal.

As in the figure below, the yellow line is the DAC output, which stays high during the first 250 ms. The green line is the 3.3 V VDD signal (Power supply) and the pink line is a GPIO output, which generate a high level output immediately after the automatic initialization by Processor Expert.@@

I'm wondering if the DAC output logic level could be programmed to 0 V during reset at the very beginning.

Thank you in advance for any kind of help!

Marie

Re: K02 DAC output logic level during Power-On Reset (POR)

Jorge_Gonzalez — Mon, 05 Oct 2015 01:21:10 GMT

Hello marie lu:

I tried with a FRDM-K22 and I do not see this behavior. This is what I get (Power ON and then I write random values to DAC):

Could you attach your project?

In particular I want to check the next points:

- What IDE (KDS, IAR, Keil)?

- Processor Expert with or without KSDK?

- Using other components?

- Is auto initialization enabled?

Regards!

Jorge Gonzalez

Re: K02 DAC output logic level during Power-On Reset (POR)

marielu — Mon, 05 Oct 2015 16:48:31 GMT

Hi Jorge,

Thank you so much for helping me working on this.

I'm using KDS 3.0.0, Processor Expert with KSDK 1.2.0. Under the projects, I also use ADC, FTM and GPIO modules, with auto initialization enabled. For emulator, I use PE micro multilink universal.

I'm working on a DC-DC power supply, and the figure I showed you is captured when the power stage is working. When the power stage is not working and only the processor operates, I get the same waveform as yours.

I would like to draw your attention to some details. In your figure, there is a small spike before DAC starts to output, which is highlighted in red circle in the pic below.

On my processor, I could also see this spike, but with higher amplitude, as shown below:

I zoom in the spike, and it shows as an increasing slope, and then drops down to zero.

The bandwidth of the scope in the figures above is 200 MHz. Since you also have the spike on your waveform, I assume it's not my measurement problem. I'm wondering what causes this voltage spike, and if there's any method to avoid it.

Thank you and best wishes,

Marie