PMIC Boost regulator short when enabled through Software

[santhakumara]

Hi,

We are using iMX6 Solo processor (MCIMX6S5EVM10AC) in our design with PMIC MMPF0100F1AEP.

we using PMIC as in default configuration mode.

In this config mode by default 5V boost reg will not be enabled and it is enabled while booting through I2C register write.

We noted that while enabling this boost regulator this 5V rail is shorted and PMIC is heating excessively.

We tried removing inductor used for regulation and this case there is no heating.

So it can be understood that while enabling Boost reg causing the circuit short.

this is volume manufacturing and few boards behaving in this way..

could any have expertise on it..what causing this to happen.

below is our circuit's Boost reg section..

regards,

santhakumar.

[igorpadykov]

Hi santhakumar

one can add additional switch as Q511 on SPF-27392 Sabre schematic,

to avoid application of power to turned off pmic.

Best regards

igor

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[santhakumara]

Hi Igor,

After seeing SPF-27392 Sabre schematic It seems it is excess circuit to control the Boost reg externally..

As i understood PMIC Boost reg can be controlled in two ways..one is what you have mentioned (using external FET) and second is Disabling or enabling the boost regulator through I2C register write..And we are on second option..

it is functioning on over 95% of boards..only few boards having this issue..for more specific,once Boost regulator enabled through I2C we have measured its voltage levels..Consider Diode (D12) on above given schematic..on the anode side it is 39V and on cathode side it is 14V..

Please suggest what would be causing this to happen.

Regards,

Santhakumar.

[igorpadykov]

Hi santhakumar

when chip is turned off, it is not allowed to

apply external voltage to it, unless it is described

specially in datasheet. Without Q511 voltage will

be applied to pmic which may cause unpredicatble

behaviour, including internal latching effects.

Best regards

igor

[santhakumara]

Hi Igor,

thanks,

in that case whether Datasheet recommends to use External MOSFET

switch..

i don't see any.

i'm asking this Since it is volume product and produced.

Now we don't see issue over 98% products.

will it produce issues over the time.

regards,

santhakumar.