LMK04828: PLL Auto Mode

Chris Hinton

Part Number: LMK04828

Hello -

We've been using the LMK04828 for a few years now, successfully. Our current initialization procedure is:

#1) We currently check against LOS<0x184[1:0]> to point manually point the PLL1 towards <0x147[6:4]> the available reference.

#2) After PLL1 locks <0x182[1]>, we then put the PLL1 into automode <0x147[6:4]=4>.

#3) Ensure that PLL1 is locked <0x182[1]>

We recently noticed that step#3 wasn't locking. We found is that the LMK locked (as per step#2) but we moved into automode too quickly. Doing the register writes by hand worked every time. Adding a small SPI delay, seemed to fixed the issue as well.

Question: do we need to wait a small amount of time between getting a PLL1 lock and going into automode? experimentally, we've found that to be the case. If so, what's the recommended time?

Thanks.

Chris H

over 5 years ago

0 Liam Keese over 5 years ago

TI__Genius 12705 points

Hello,

I assume you have all the inputs enabled for auto mode prior to this sequence?

It is possible even thought the PLL1 is locked that you are switching over to auto mode before the input signals validation and calibration has completed.

How long between when you select the manual mode and then switch to auto?

Regards,

0 Chris Hinton over 5 years ago in reply to Liam Keese

Intellectual 260 points

Hi Liam -

Q: I assume you have all the inputs enabled for auto mode prior to this sequence?
A: Yes, were using CLKin0+1, so 0x146[5:3]=3

It is possible even thought the PLL1 is locked that you are switching over to auto mode before the input signals validation and calibration has completed.

Q: How long between when you select the manual mode and then switch to auto?
A: It's unclear. We did not have a probe connected.

Thanks, Chris H.