PMIC SW3B voltage issue

[mrudangshelat]

Hi, In my iMX6D based design we have used the MMPF0100 to supply voltage and CPU/SOC core voltage and it's interface devices. Now I have provided SW3A supply to DDR3L but SW3B is not powering any interfaces (floating). When I measured voltage during power bring-up, I have observed that SW3A is providing me proper voltage (1.5V) but SW3B is giving me around 2V. Why is that so?

I have not yet programmed PMIC. I have just measured pre-programmed OTP voltage.

Could you please help me to solve this issue?

Thanks

Mrudang.

[atillametetured]

Hi Mrudang,

The voltage you are getting is not random. Since you do not have an inductor and capacitors at the output you are not getting a stable voltage output. Plus, since you did not connect the feedback of SW3B (which I presume) the feedback circuit cannot adjust itself to the right voltage. I also dont think the voltage is 2V precise, connect a probe and you will see the swinging voltage levels.

Almost all Switchers do this, you are right. LDOs on the other hand do not need feedback at the output, so no, LDO's will be fine without any external componenets (at least you will get the right voltage).

Regards,

Mete

[mrudangshelat]

Hi Mete,

Here i am reattaching my schematic circuit. I have inductors and decap capacitor at output. I have also connected SW3B feedback. though I am getting around 2V on SW3B. And i have measured peak-peak voltage which also very nominal.

FYI, I do have 4 unused LDOs and 2 unused switcher in my design but I am able to get all voltages as per OTP except SW3B output.

Thanks,

Mrudang

[atillametetured]

Also to clarify, when a Switcher is unused, what I understand from that is peripherals are not added. You have added all peripherals correctly. What I perivously wanted to say was the case in absence of an inductor and output capacitors.

[mrudangshelat]

Hi Atilla and Mete,

Let me config SW3B as you have mentioned, and will update you.

Thanks,

Mrudang

[mrudangshelat]

Hi Ross and Mete,

We have tried to configure OTP register for individual supply rail for SW3B, but we are not getting OTP 1.5V supply. we are still getting random value voltage 2.1V on SW3B.

Could you please help us? Or is any other way to get configure value.

Regards,

Mrudang

[atillametetured]

Hello Mrudang,

I am sorry to hear that. Well, from my experience, I can advise you to one by one check all connections that your SW3B rail makes.

Once I had a problem like this and I found out that it was a poor buffer design that pulled up my 1.8V to 2.2V. I can also advise you to do this; remove any connections to SW3B rail on your pcb if that is even bossible (non conducting tape under pins and cable connections). Measure it again and see if that is still the case. This way you can trace the problem back to its source.

I hope this helps.

Best regards,

Mete

[atillametetured]

Hi Mrudang,

That design seems fine. Excuse me for that I have misunderstood you. However you are still omitting the fact that you did not program the PMIC. Since you bought a pre-programmed one, and all pre-programmed PMICs come with same settings regarding SW3 Mode, that is, SW3 is set to A/B Single Phase. However your configuration demands SW3A/B Independent settings.

I do not know if you can change the settings of SW3 for a pre-programmed PMIC so that SW3A/B is set to independent mode. I do not think its possible because SW3B_CONFIG[1:0] bits are OTP but its best someone from NXP answers that. We used a NP one for flexibility in our project.

Also I do not see any input capacitors in your design but I assume you have them.

Regards,

Mete

[RossMcLuckie]

This is what I tried to explain earlier in the thread. The registers are fully programmable, the OTP part is purely for pre-loading registers at start-up, the register containing the SW3B_CONFIG bits remain R/W, as shown in the datasheet, all register status, whether Read Only or R/W is defined in the datasheet.

Regards

Ross

[atillametetured]

Hello Ross,

Thats actually good news to hear. I took it that since its named one time programmable, there is no means of changing the fuses once blown. It turns out its OTP only for the start up values as far as you have put it. Thanks for this information. Now it makes a lot more sense.

Regards,

Mete

[RossMcLuckie]

Yes I can understand why that could be confusing, the OTP refers to the start-up configuration, not the registers themselves, but if the registers are labelled OTP, that probably doesn't help.

I just found this in the datasheet, which again highlights the likely issue here -

Regards

Ross

[mrudangshelat]

Hi Ross and Mete,

We have tried to configure OTP register for individual supply rail for SW3B, but we are not getting OTP 1.5V supply. we are still getting random value voltage 2.1V on SW3B.

Could you please help us? Or is any other way to get configure value.

Regards,

Mrudang

[art]

If you have no connection to the SW3B pins (all SW3B pins are floating), the voltages can be random there.

Have a great day,
Artur

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[mrudangshelat]

Hi Artur,

Thanks for your reply.

May be you are right, but I also do have SW4 which is floating but it provides me proper voltage ~3.13V instead of 3.15V.

And I have applied externally restive load 220R parallel to C171 on SW3B but still it gives me random O/P voltages. 

Does all floating Switchers and LDOs gives random O/P voltages? 

Please provide me your valuable feedback.

Thanks,

Mrudang

[RossMcLuckie]

Hi,

You should review the PF0100 documentation, in particular the datasheet, can be found here -

14-Channel Configurable Power Management IC|NXP 

All variations of the PF0100 power up expecting SW3AB to be in single phase configuration, from datasheet -

Which would be configured in hardware as follows -

However you have your hardware configured for independent outputs -

So until you program the PF0100 registers to match your HW configuration the outputs will not be as you expect.

Regards

Ross

[mrudangshelat]

Hi Ross,

Thanks for reply.

I am using pre-programme default configuration of MMPF0100. And default output voltage full fill my system required voltages to bring-up. My system is running well. But as per "Default Configuration voltage" I am unable to get SW3B = 1.5V. I have highlighted in below image. Instead of that I am getting SW3B = 2V. Kindly help me to solve this issue.

Thanks,

Mrudang

[RossMcLuckie]

Hi,

I support iMX products, but have used the PF0100 in several designs, so although not an expert on its operation my understanding is as follows -

The default table shown above assumes SW3 to be in single phase mode, your hardware is configured for independent mode, for single phase SW3BFB should be left floating, your design has it connected to the SW3B output, so I'm assuming this is where the trouble lies.

All of this is from the PF0100 datasheet, rev 16, I would suggest you review this document again and make sure you understand all the set ups and settings.

Your design is configured as independent -

but the default register setting expects single phase -

If you wanted to test this, looking at your schematic snippet attached I think you can convert from independent to single phase by -

• Removing L6 (and most likely FB13, not sure if you have anything connected to the SW3B output)
• Shorting SW3BLX (one of the L6 pads) to the SW3AFB net
• Possibly you may need to remove C170, C171, C229 (requirement is to have SW3BFB open circuit, don't think the capacitors would be an issue, could try without removing first, if still an issue remove)

This should let you see 1.5V at SW3AB, with 2.5A capability.

To use your independent configured set up I believe you will have to reprogram one register value containing the SW3_CONFIG setting -

Can be found here -

Hope this helps.

Ross