MPC5777C : Clock configuration failure when selecting PLL

[daniel_fernande]

Hello, 

I want to configure MPC5777C to use an external oscillator at 40 Mhz (connected to EXTAL pin) with PLL0 and PLL1 as described in the following diagram : 

The problem I get is that after the register SIU.SYSDIV is written (see below), the microcontroller resets (in loop)

All PLLs apparently lock correctly, it is when selecting PLL1 as system clock that the problem occurs.

Do you have any idea what is happening? how can I investigate further and find out the cause of the reset? (SIU.RSR indicates Power On reset)

Thanks for the support

[daniel_fernande]

Update : We fixed the issue 

The problem was on the power supply not providing enough current when switching to PLL clock

[lukaszadrapa]

Hi Daniel,

yes, power supply is usually source of similar issues. Notice that there's Progressive Clock Switch feature which can help to reduce voltage drops or overshoots up to certain level but it's still required to have the power supply strong enough...

Regards,

Lukas