LP8764-Q1: BUCK1_PG not correctly coming up

Hi Alleyn,

Thanks for reaching out. For better understanding can provide below information.

Alleyn Bowen said:

Currently this is not working properly

1. Can you provide scope shots enabling us to see what is happening?

Another question that since device has PGOODs available ( either in GPIO1,6 or 9) then why did you not use any of those?

BR,

Ishtiaque

Hi Ishtiaque,

Thanks for the reply.

Regarding your question: I have 3 different configurations of the LP87644, so I needed to have 2 different PGOODs from the chip. For config 2 below: I need to have EN1 (GPIO1) enable the 1V8 rail and then I monitor PGOOD from just 1V8, then I enable 1V2 and monitor PGOOD  from just the 1V2. So my assumption was it was easier to implement this in the FSM and just states, as there is only 1 PGOOD.

- Config 1: 4 phase 0V8 rail, Config 2: 1 phase 1V8 (comes up first), 3 phase 1V2 (comes up second), and 2 phase 1v0 (comes up first), 2 phase 1v2 (comes up second).

I am currently testing just config 1 which only has 1 output so for this one I could have just used PGOOD, but I need the other ones working too. I am currently just testing config 1. I have also added PGOOD output on GPIO6 now to the NVM config, and it also isn't behaving correctly.

Here is the plot:

- I single trigger on VOUT1: which comes up as expected, but GPIO2 is turned on before VOUT1 is high. I have modified the json file to bring PGOOD out to GPIO6 for analysis, but PGOOD is always high. I have included the .json as a .txt file for you to look at:

Note: It makes sense that GPIO2 would immediately go high, if PGOOD internally was always GOOD, so maybe there is a register that not set correctly. If you help me to first get PGOOD working properly (on GPIO6), we can progress from there.

These changes are done:

GPIO6_OD=0x1

3566.sample_template.txt

Thanks,

Alleyn

Hi Jari,

Thanks for the reply, this has resolved the problem with GPIO2 on my first config. I will now develop and test the other configs. PGOOD also responds now.

Thanks,

Alleyn

Hi Alleyn,

Excellent news. Please share if you manage to resolve another config as well so will close thread after confirmation.

Br, Jari

Hi Jari,

I have another minor issue: see plot showing GPIO1 (1), GPIO2 (2) and VOUT (BUCK_1_2_3_4). I am getting spurious activity on the GPIOs, prior to the rails being enabled. You can see after I enable GPIO1 (offscreen), just before the VOUT starts to ramp. There is a 34us pulse on GPIO1 and GPIO2. These occur every ~210ms, and the pulses stop after VOUT has been enabled. Is there anything that can be causing this?

I have also added the latest start machine (.txt):

8308.sample_template.txt

Thanks,

Alleyn

Hi Alleyn,

Not sure what exactly is causing this behavior but we have identified some updates that should be done.

For example, if you change the following triggers to normal instead of immediate.

And update the Enable sequence with Jump instead of END as following. 

Let's see if you still get the same behavior. 

BR,

Ishtiaque

Thanks Ishtiaque,

I modified that but also change BUCK1_VMON_EN=LOW in the ACTIVE state when disabling BUCK1 before GPIO1 is set high. This seems to resolve the spurious toggling issue. BUCK1_VNMON_EN is only set high when I turn on the BUCK1 in the ENABLE state.

I will now look at Config2 and Config3, and let you know if I have any issues.

Regards,

Alleyn

Hi Alleyn,

Good to hear that it seems to resolve your issue. So for now I am going to put this thread on wait status but do let me know if you do not have anything further so that I can close the thread. 

BR,

Ishtiaque