LMZ23605: LMZ23605

Hi Frank,

Thank you for that information. Please also share your schematic and layout and I would be happy to review these with you.

Thank you,

Joshua Austria

Hi Joshua,

Thanks for the response.

This is a classified project so I can't share much. The schematic is shown below:

We removed the part from the board and found that the Exposed PAD/PGND was shorted to AGND (~0.8 ohms).

I think these should be isolated and connected only on the circuit board.

Also we are leaving the enable line open circuit (floating) as mentioned on page 18 of the datasheet as there is an internal pull-up to enable the regulator.

The absolute maximum rating in the datasheet is 5.5V on the enable pin. We are measuring 6.4V with the enable pin floating. I this an issue?   

Thanks,

Frank 

Hi Frank,

Enable should not be higher than 5.5 V as this goes above the abs max ratings as stated within the datasheet. In the case that Enable is left open, the internal UVLO is stated to occur at 4.3 V (please see section 8.2.2.2 of the datasheet).

Were the exposed pad and AGND welded to each other or were they electrically shorted i.e. via a continuity test.

Would it be possible to do an ABA swap with this IC and a fresh EVM? The purpose of this test is to determine if it is an IC issue or a schematic issue that may be causing the issue.

Thank you,

Joshua Austria

Hi Joshua,

The exposed pad and AGND were measured with an ohmmeter and read ~ 0.8ohms (so electrically shorted).

We ordered some actual parts and an EVM for the LMZ23605 so what you stated is a good next step (ABA swap).

Thanks!

Frank

Hi Frank,

Sounds good. I will await the results of this test and we can continue our debug from there.

Thank you,

Joshua Austria

Hi Joshua,

We replaced the LMZ23605 on the original board that had the failure, and the board is working fine now.

So we are still wondering what happened to the part. 

I also got the eval board for the chip and got that running. I did notice that on the Eval board with the enable pin floating

the pin floats up to 6.4V just like our boards do. The max on this pin is 5.5V per the datasheet. Is this only for an externally driven enable?

Thanks,

Frank 

Hi Frank,

Is this the voltage that you are seeing on the pin? Which board are you using (DEMO or EVAL)?

Thank you,

Joshua Austria

Hi Joshua,

It is the voltage on the enable pin of the chip (pin 3). I am using the EVAL board.

I removed Renh so the enable pin is unconnected to anything and floating similar to the 

way we are using it.

Thanks,

Frank

Hi Frank,

Understood. Thank you for confirming.

Yes EN can be left floating for this device as it has an internal pull-up. Just a couple more questions:

What is the input/output profile that this device was running in when the device failed (VIN, VOUT, IOUT, FSW)?

Was L2 shorted or connected?

Thank you,

Joshua Austria

Hi Joshua,

VIN= 12VDC, VOUT= 3.3VDC, IOUT = 3A max

The sync is not used and this pin is grounded per the datasheet, so the free running FSW should be 812kHz

Thanks,

Frank

Hi Frank,

Thanks for that. Please also confirm my previous question about L2. 

Also please share your layout when you get the chance so I can review that as well.

Thank you,

Joshua Austria

Sorry forgot- L2 is not shorted. I'm not sure about sending the layout since it is classified. I'll find out.

Thanks,

Frank

Hi Frank,

Sounds good. 

Is this inductor a part of the input filter for a device downstream of the module? Can this be shared?

The layout would be the next step in reviewing your issue. If there is a concern about the publicity of this forum, you can always send me a direct message on E2E.

Thank you,

Joshua Austria