LM10506: LDO used outside of specification during power ramp-up

Lars Pinnerup Frederiksen

Part Number: LM10506

Hi,

We use the LM10506 in a design where the 3.2V LDO is the primary supply for the processor on the PCB. The processor has its own internal core supply (buck converter). During power up of the LM10506, the LDO is overloaded in a period of approximate 500us. Please refer to the attached scope dump.

I would expect that the characteristics of the 3.2V curve is due to a combination of the total filter capacitance on our board and probably the LDO going into current limitation state until the output current has fallen below the specified 100mA output capability.

Question: Is it a problem for the LM10506 LDO that it for a period of approximately 500us delivers max. 260mA during power up?

In attached scope dump:

C1: LDO output current, C2: LDO output voltage, C3: PWM signal out of the processor (not used here), C4: Processor buck converter voltage.

Thank you in advance.

Br, Lars

over 2 years ago

0 Emily Kong1 over 2 years ago

TI__Expert 3350 points

Hi Lars,

It is not uncommon for a device to max out at a slightly higher current than it is rated for during testing. The LM10506 does have a current limiting feature that should protect the PMIC as well as any external circuitry, but we cannot recommend operating this device outside of specification. The LM10506 is currently an NRND device; is this is a legacy design where this issue is only just now being observed?

Best,
Emily

0 Lars Pinnerup Frederiksen over 2 years ago in reply to Emily Kong1

Prodigy 10 points

Hi Emily,

No, this a new configuration of the LM10506 due to change in product MCU. I understand that you cannot recommend going outside the specification, but as I have no insight into the design of the internals of the PMIC I cannot judge whether or not the showed energy dissipation in the scope dump has short or long term consequences for the PMIC. I'm not looking for an official exemption to the specification but rather expert judgement on this specific use case and whether or not it is damaging for the PMIC or not.

Br, Lars

0 Emily Kong1 over 2 years ago in reply to Lars Pinnerup Frederiksen

TI__Expert 3350 points

Hi Lars,

Due to this being an older device with limited documentation availability, I will do some digging and get back to you early next week.

Best,
Emily

0 Lars Pinnerup Frederiksen over 2 years ago in reply to Emily Kong1

Prodigy 10 points

Hi Emily,

Very much appreciated. Thank you.!

Br, Lars

0 Emily Kong1 over 2 years ago in reply to Lars Pinnerup Frederiksen

TI__Expert 3350 points

Hi Lars,

Unfortunately, we don't have any data I'm able to provide you on current limit wear tests to provide a specific gauge, but exceeding the current limit will in general wear out the fet so the PMIC will exhibit decreased reliability and longevity.

Best,
Emily

0 Lars Pinnerup Frederiksen over 2 years ago in reply to Emily Kong1

Prodigy 10 points

Hi Emily,

Ok, I understand. I appreciate your effort, so thank you.! Have a nice day.

Br, Lars

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LM10506: LDO used outside of specification during power ramp-up