TPS7A4001 unstable Issue

Hi Derek,

Thank you for the scope shot; however, could you tell me what each signal is?

Was this seen on multiple TPS7A40 devices? Did switching to TPS798 always yield a correct waveform?

Very Respectfully,
Ryan

HI Ryan:

The Green is the LDO input wave. The Yellow is the LDO output wave.

Switch to TPS798 is always correct wave.

Hi Ryan:
I just check with customer, it looks like the Fb pin has disturb.
Even add a strong power supply no drop (Green line), there will be still wave like yellow.
And the LDO output wave(yellow line) looks like the LDO start work then stop continuely.
So what will cause the LDO stop, besides the EN pin? Any other condition?
Why the Fb disturb will cause this wave?

Hi Ryan:

Any comments on this issue?

Hi Derek,

This waveform looks a bit odd - could you provide a scope capture with the load current? And could you also look at the start-up waveform (with Iout)?

This looks like the load is doing something odd to the device. Additional output capacitance typically help for dynamic load events.

Regards,
David

Hi David:

Thanks for your reply.

We have added 220uF capacitor at the input and output to try. The result is same.

An we find the LDO looks like stop work then start work again continuesly.

Hi David:

Please see the power up output wave.

Hi Derek,

Looking at your output on turn-on it looks like you are reaching the 20V than going into a weird state.

Do you know what is causing the output to fall? In past cases it's been the load of the part drawing too much current. I would start there by removing or disabling the load.

Regards,

David

David:

Remove the load, the result is same.

Hi Derek,

Does the start-up waveform change without the load?

Thanks,
David