How is this LDO working?

[FreshmanNewbie]

I'm using this LDO.

If I replace to this LDO, drop-in replacement, then the system (microcontroller) works.

The LDO provides power to the microcontroller. Due to high noise at the output of the microchip ldo, the supply thresholds of the microcontroller are not meeting and hence the system fails.

Same circuit is present like the Typical application circuit of both devices. 1uF is the output capacitor.

I figured out that the output noise seems to be high on the microchip part. Maybe, that's why the microcontroller power that is provided by the LDO, is not meeting the threshold.

In fact, the PSRR value is high for the microchip part. Can someone tell me what is the reason that the microchip provides high noise and any suggestions to rectify this as I have many microchip parts that are present in the boards that are shipped

 

[KlausST]

Hi,

Due to high noise at the output of the microchip ldo, the supply thresholds of the microcontroller are not meeting and hence the system fails.

Generally I doubt this.
If your circuit is according datasheet and the load is within specified range, then the output voltage will be stable.

Sadly you neither give schematic nor thechnical values.

"1uF" is no complete description for a capacitor. Please check on your own whether your capacitor meets the recommendations of the regulator datasheet(s).

Can someone tell me

You need to give full informations first...

Klaus

 

[dick_freebird]

Many LDOs are inadequate to the task of attenuating HF
ripple, as produced by swotching supplies upstream. A
smaller number are meant specifically for this (HF PSRR).
You need a high loop BW if you are getting DC PSRR by
loop feedback, and many older LDOs just are too slow.

But maybe this is telling you to pay more attention to the
incoming supply ripple voltage, or the uC's transient
demand current (w/ any sourcing inductance or poor
quality close-in LDO supply decoupling).

Grab your 'scope and go hunting for "not right".

 

[danadakk]

Not all capacitors are equal ESR (bypass effectiveness) for the same capacitance :

OSCON in above are Polymer Tantalum.


Regards, Dana.

 

[Taihung]

Hi
One maximum output is 150mA, one is 200mA. Your uC system maybe consumpt higher 150mA.