LM73606: LDO voltage drops under load

Jessica Kinchin

Part Number: LM73606

Hi,

I have a design that is from the power designer for 1.2V @ 6A using 18V input, with PG connected to 3.3V and there is a EN voltage of about 5V (PG from previous supply). I use a bias of 3.3V and testing the supply with an electronic load.

When I load it @ 1A the LDO goes from about 3V no load to 3.2V loaded as expected

when I increase the load to 1.5A the LDO drops to about 2.1V and output collapses

I use the same device to produce 3.3V (the one also used as the bias on the 1.2V) and that functions to full 6A using a similar design with values for 3.3V instead of 1.2V (mainly inductor change and feedback) but this uses its output for bias and is auto startup

Any help would much appreciated I need the full current as it is to provide a DDR4 VDDQ

Jessica

over 6 years ago

0 Marshall_Beck over 6 years ago

TI__Mastermind 35190 points

Can you share schematic?

0 Jessica Kinchin over 6 years ago in reply to Marshall_Beck

Prodigy 20 points

Hi Marshall,

Thank you for your reply I am on UK time so it has taken me a while to respond.Here is schematic as a pdf

Jessica

wo10707_inst3_19-08-02_0901xx.pdf

0 Marshall_Beck over 6 years ago in reply to Jessica Kinchin

TI__Mastermind 35190 points

No worries, we will make up for lost time with a speedy response on our end :)

Let me digest the problem.I will follow up with you later today, so you can have an update/answer with some data (if needed), your Thursday morning .

0 Marshall_Beck over 6 years ago in reply to Marshall_Beck

TI__Mastermind 35190 points

Thinking this through, it might be an issue with the bias.

It looks like you are powering the device internal control circuitry through the bias pin.

To eliminate that the external supply you are giving is causing an issue with powering the control circuity, can you try the following steps:

1. Leave bias floating and re-run test you did earlier. The LDO internal to the device with generate the required 3.3V output

2. If that test resolves the issue, then use an external supply of 3.3V (say lab DC supply) to power through bias pin.

This will determine if your external supply (UTIL_3V3) is an issue.

Please let me know how it goes.

0 Marshall_Beck over 6 years ago in reply to Marshall_Beck

TI__Mastermind 35190 points

Jessica, I assume this issue has been resolved?

I am closing this thread due to inactivity, please let us know if there are still issues.

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LM73606: LDO voltage drops under load