PLLs settings changing on i.MX53?

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PLLs settings changing on i.MX53?

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sekharbabu
Contributor I

My design is based on i.MX53 processor. I am facing strange issue on my board.

I am using I2C-3 interface to drive 5 LED driver ICs, each IC can drive upto 15 LEDs. I have configured 210ms time between the LEDs ON/OFF. The I2C clock programmed to default, I am measuring it as 13.89KHz. I2C-1 is used for Camera and PMIC. I have modified the OBDS software to test my on board 75 LEDs.

The issue is when I execute LED test, some times the LED ON/OFF time is different from what I programmed (210ms) . On each board power cycle it is showing either 210ms or 840ms LED ON/OFF time. The I2C-3 clock is same on both conditions that is 13.89KHz. Why LED ON/OFF time is changing from 210ms to 840ms. I guess PLL settings are getting changed on each power cycle. Can somebody suggest me how to overcome this issue?

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igorpadykov
NXP Employee
NXP Employee

Hi sekhar

one can check PLL frequency using CCM_CCOSR register.

Also I would suggest power-on sequence, it may affect.

Best regards

chip

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sekharbabu
Contributor I


I checked CCM_CCOSR register content it is showing 0x000A0001 in both the cases

And the power sequence double checked, it is good. All the voltage levels are proper.

If I put the oscilloscope probe on 2.775V (VDAC), it is going into 840ms LED on/off time .....

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igorpadykov
NXP Employee
NXP Employee

Hi sekhar

regarding CCM_CCOSR register - I meant to

output PLL (which is source of I2C) on CLKO signal

(check Table 4-2. Pin Alternate Modes  I.MX53 RM) and measure

with oscilloscope. Please use Figure 18-2. CCM Clock Tree

to find clock (and PLL) used for I2C module.

To exclude programming software errors, I would suggest to

run OBDS and check if issue will persist.

On-Board Diagnostic Suit for the i.MX53 Quick Start Board : On-Board Diagnostic Suit for the i.MX53 Quick Start Board

Best regards

chip

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