iMX8MP & PCA9450C cannot start - 32kHz duty cycle

[sfatyushkin]

We're starting to test our board with the IMX8MP and PCA9450C. On our board, the PCA9450C CLK_32K_OUT output is connected to the iMX8MP RTC_XTALI input.
We see that the duty cycle at the CLK32 output is significantly different from 50%.
This situation is observed on both of the two boards. We're using an ABS05-32.768kHz-6-T cristal oscillator.
What are the requirements for cristal oscillator for PCA9450C ?

Best regards,
Serge

[TomasVaverka]

Hello Serge,

Based on the PCA9450C datasheet (Section 9.2.2.1 Crystal selection), here are the key requirements for the external crystal:
- Load capacitance: 6pF to 15pF
- ESR: 30kΩ to 100kΩ
- Frequency tolerance: 5ppm to 30 ppm

The oscillator circuit uses two load capacitors (CL1 and CL2). If both capacitors are equal, each should be approximately:
CL1​ = CL2 ​≈ (2 × CLoad​) − Cparasitic​

Regarding the duty cycle, the CLK_32K_OUT pin specification allows a duty cycle between 30% and 70%, see Table 88.

BRs, Tomas

[sfatyushkin]

Hello Tomas,

1. Our crystal resonator meets these requirements (Load capacitance: 6pF, ESR: 90kΩ, Frequency tolerance 20 ppm), two load capacitors according, load capacitors are selected according to these requirements 
An important parameter is the power of the Crystal (Drive Level). Please tell us which quartz resonator is used in the EVK.

Best regards,

Serge

[TomasVaverka · Accepted solution]

Hello Serge,

Please see below from the attached FRDM-IMX8MPLUS BOM file.

BRs, Tomas

[sfatyushkin]

Thanks a lot!
I see that our resonator has the same characteristics.

Best regards,
Serge