LM5145: LM5145 Standby Mode has output of 1.2V

Wenhao,

1. Standby allows VCC to rise and be stable before the circuit starts switching. It allows the IC to shut down when it's far from switching (VIN < -0.4V) but get ready when switching is about to happen (VIN rising).

2. Strange that it's similar to COUT*(Rfb1+RFB2) since these C and the Rs are in parallel. Can you please share your schematic.

Thanks,
-Sam

Hi Sam,

You can refer to LM5145 EVM User Guide. Ive also attached it.LM5145 EVM module.pdf

Wenhao,

Sorry, forgot you were using the EVM.

Is this an unmodified EVM? It seems strange that VOUT should increase especially since your feedback resistors are connecting to GND. Does this work as expected when the EVM is powered on?

-Sam

Yes, it was normally working, except that, everything is normal. Will it be caused by electronic load?

It may be caused by the electronic load. Try disconnecting the eLoad and check the voltage.

Sam,
Still, LM5145's standby mode output exists. I am considering to test HO and LO to see if 5145 will accidently activate the MOSFET. This issue exists in both EVM i purchased on TI store.

That would be a good test.

I ordered some fresh EVMs so I'll test in the lab when I get them.

-Sam

Wenhao,

One of our engineers has tried to recreate this with our EVM but we were not able to. Can you please share your entire test setup so we can be sure we're recreating exactly the same way as you.

-Sam

Hi sam,

I will take a photo of relevant test setup together with experimental waveforms;
Thank you!

Wenhao

Hi Sam,

The following is my setup when testing LM5145, where the input is 10V, sharing the same ground with output. I have already taken 4 output capacitors to test relevant loop compensation parameters and there are still 4 left on back board. Thank you!

Wenhao

Wenhao,

Please also share a picture of the back of the board.

I'll be receiving EVMs shortly. Once I do I'll recreate your tests with your setup.

-Sam

Hi Sam,

I will take the pic later i have access to lab. Thank you ahead!

Wenhao

Hi Sam,

Sorry i did not understand what you meant. Did you actually mean i should tie EN to GND with a connecter? On the other hand i think it could pull down EN making the device stay in shut-down mode. Thank you for you answering! Do you still need my experimental setup now? ihave already taken a pic of back of the setup.

Wenhao

Wenhao,

You said you see an output of 1.2V when the device enters standby mode. This mode would be entered by connecting EN to GND. Is this how you entered standby?

I do not need the picture if this is resolved.

-Sam

Hi Sam,

I did not connect EN to GND. As I can understand in datasheet. 5145 will only enter standby mode when VEN is between 0.6 to 1.25V. So i just let it be, i changed nothing of EVM. Naturally, EN is supposed to connect to VIN via a resistor dividor. If nothing changed to EVM but just set VIN=10V, 1.2V output is still there. Sorry to ask you again. Could you please try if just connect VIN and VOUT, GND and nothing changed to EVM, in this case, test output? If you have a 1.2V output, then you recreate it, please tell the cause. Thank you very much!

Wenhao

Wenhao,

I understand now. I've been able to reproduce this in the lab. I will investigate and get back to you.

-Sam

Hi Sam,

Thank you that you have recreated the issues. Looking forward to your reply. 

Wenhao

Hi sam,

Now i understand the reason and i will inform my team about this issue. Another question please, can this standby output issue be solve by using Rsense mode? On the other hand this will increase the total cost and size because large sensing resistor needed. Need your confirm. Thank you!

Wenhao