TPS63002 L1 - L2 shorted to GND

Hi Marek,

I would recommend you to do new version of the layout because current version of the layout need improvement. To see proper layout for the IC please look into the datasheet, paragraph: 10.2 or 11.2: Layout Example.

What is the part number of the inductor 4.7H? What is the saturation current of the inductor in your application?
Why are you using 4.7uH?

Best regards

Lubomir Fenic

I'll change layout in new version. But now I need to do something with this production.
At beginning we didn't know that layout is so crucial. TPS63031 works great in the same layout.
For right now my inductor is TDK NLCV32T-2R2M-PF.
The saturation current of the inductor is ~~ 200mA

Another think that till now we didn't have that problem (same PCB).

Hi Marek,

layout is specially critical for high switching frequency DC/DC converters.
Very good guidelines you can find in this application note: www.ti.com/.../slyt614.pdf

Both converters are using average current mode control but significant difference is in current limit.

TPS63002: maximum value of the average current limit is 2000mA. This value of the inductor current can be reach during start up phase. The waveform of the start up current you can see in datasheet, Figure 19. The saturation current of the selected inductor NLCV32T-2R2M-PF is around 1A. This inductor is not suitable for TPS63002 in terms of the current saturation. So I recommend to check start up inductor current. I believe that you need to select inductor with saturation current above maximum current limit of the TPS63002.

TPS63031: maximum value of the average current limit is 1100mA and selected inductor is not in deep saturation.

I would recommend to check voltage waveforms on the L1 and L2 pin of the both converters with maximum input voltage applied. Because of the not optimal layout there can be voltage spike which is above recommended value.

Best regards

Lubomir Fenic

Hi

I taked waveforms on the L1 and L2 pin at start conditions.

L2 in  start up phase:

L2 in normal condition (zoom to frame):

L1 in start up phase

Inductor current is limited, but inductor is not damaged. And every thing was ok in first 100 PC so I'm confused. I'm wondering what can be wrong in this production.
What is root cause of short circuit between L1 and PGND. So what do you think about waveforms.

Hi Marek,

as we discussed:
- check if you can use TPS630031-IC with lower current limit
-AN for extending soft start: www.ti.com/.../slva553.pdf

Best regards

Lubomir Fenic

Thank for call. Thank you very much. You help me a lot.
What do you think about this inductor WLPN303015M2R2PB?
I sat curve looks better then the other (it's more "flat").

Hi Marek,

inductor is little bit better WLPN303015M2R2PB but saturation current is 1.48A. SO it means that inductor at this current is losing 30% of inductance. So I recommend you to test it in your application.

Best regards

Lubomir Fenic

Hi Lubomir

I found another interesting position:

IHHP 0806 ABER2R2M01
IHHP0806AZER2R2M01
IHHP1008AZER2R2M01

I think that is that same inductor but in different package.

So what do you think about them? In term of parameters I think they are very interesting.

Best regards 

Marek Dudek

Hi Marek,

according to the datasheet information inductor IHHP1008AZER2R2M01 has the higher saturation current.
I would recommend you to test this inductor in your application.

Best regards

Lubomir Fenic