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Dirk_Haller
Level 1
Level 1
First question asked Welcome!

Hello all,

 

we have a TC277 (SAK-Device) design here and we experience frequent PLL cold start problems at tempoeratures between -37 to -40°C. Approximately 30% of our units are affected.

The setup when this problem occours is as follows:

Cool down the CPU-Board (with or without housing) to -40°C and hold this temperature for 1/2h to ensure that everything is well cooled through.

Perform a power on start of the device (plug in power suply)

The following effect can be observed:

With the debugger it can be verified that the TC277 starts up on it's internal backup clock and enters the C startup code, until it reaches the code part where the PLL is programmed:

 

if defined SCU_PLLCON0 && defined __SCU_PLLCON0_VALUE
#if __SCU_PLLCON0_INIT
SCU_PLLCON0.B.VCOBYP=1; /* Enabled the VCO Bypass Mode */
while(SCU_PLLSTAT.B.VCOBYST==0); /* Wait until prescaler mode is entered */

#define __SCU_PLLCON0__VCOPWD_VALUE ((__SCU_PLLCON0_VALUE>>1)&0x1)
#define __SCU_PLLCON0__NDIV_VALUE ((__SCU_PLLCON0_VALUE>>9)&0x7f)
#define __SCU_PLLCON0__PDIV_VALUE ((__SCU_PLLCON0_VALUE>>24)&0xf)
SCU_PLLCON0.B.PDIV=__SCU_PLLCON0__PDIV_VALUE;
SCU_PLLCON0.B.NDIV=__SCU_PLLCON0__NDIV_VALUE;
SCU_PLLCON0.B.VCOPWD=__SCU_PLLCON0__VCOPWD_VALUE; /* power down VCO */

#if __SCU_PLLCON0__VCOPWD_VALUE==0
/*
* Configure PLL normal mode.
*/
SCU_PLLCON0.B.OSCDISCDIS=1; /* Automatic oscillator disconnect disabled */
SCU_PLLCON0.B.CLRFINDIS=1; /* Connect VCO to the oscillator */
while(SCU_PLLSTAT.B.FINDIS==1); /* Wait until oscillator is connected to the VCO */
SCU_PLLCON0.B.RESLD=1; /* Restart VCO lock detection */
//DHA: Hier hängt es!
while(SCU_PLLSTAT.B.VCOLOCK==0); /* Wait until the VCO becomes locked */
SCU_PLLCON0.B.VCOBYP=0; /* Disable the VCO Bypass Mode */
while(SCU_PLLSTAT.B.VCOBYST==1); /* Wait until normal mode is entered */
SCU_PLLCON0.B.OSCDISCDIS=0; /* Automatic oscillator disconnect enabled */
#endif

At the line, where the VCO-Lock is polled the microcontroller gets stuck: while(SCU_PLLSTAT.B.VCOLOCK==0);

This means, that the VCO cannot lock into a valid/stable frequency.

As sayed, this problem occours only at 30% of the devices and only in a temperature window between -40°C to -37°C.

The problem does not occour when the devices are powered at a higher temperature (e.g. -30°C) an then cooled down to -40°C. It only occours when pre cooled before power on. Also interresting may be, that the problem does not exist at very high ambient temperatures (e.g. 125°C).

We have searched for possible causes and couldn't find a cause or solution.

Tests we have made so far:

- External clock oscillator (MEMS oscillator) is up and delivers clean square wave with 20MHz

- 1.3V and 3.3V supplies are up and stable. No glitches found

- Supply-Noise is around 30 to 40mVpp on both rails

 

Does anyone have experienced similar problems or has heard of it or has any proposal what to check or do next?
We are running out of ideas what to do next.

If you have any hint or thoghts on this issue, i would appreciate any help or discussion about it.

Thank you in advance,

best regards,

Dirk

 

 

 

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1 Solution
Aiswarya
Moderator
Moderator
Moderator
10 solutions authored 25 replies posted 50 sign-ins

Hi,

Could you please refer to the sections PLL_TC.005 and PLL_TC.007 of TC27x_ErrataSheet and check if the description has some relevance to your issue?

Please note that even though the description of the section PLL_TC.005 talks about high temperature, please check by adding the workaround and see if there is any improvement.

Regards,
Aiswarya.

View solution in original post

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1 Reply
Aiswarya
Moderator
Moderator
Moderator
10 solutions authored 25 replies posted 50 sign-ins

Hi,

Could you please refer to the sections PLL_TC.005 and PLL_TC.007 of TC27x_ErrataSheet and check if the description has some relevance to your issue?

Please note that even though the description of the section PLL_TC.005 talks about high temperature, please check by adding the workaround and see if there is any improvement.

Regards,
Aiswarya.

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