LM3150-250EVAL: OVP test

Hi,

Thank you for sharing the waveforms.

Yes, you are correct. The device will recover when the FB pin falls below .72V.

For my understanding, you are applying an external voltage to the FB pin and then you remove this external source completely. Is this correct?

Thank you,
Katelyn

Hello,

Yes. I inputted 0.8V-bias to FB-port by mecha-switch. After inputted bias, it is open, not 0V.
Why does LM3150 stop operation?

Regards,
ACGUY

Hello,

It stops operation due to the FB being pulled high (0.8V) or greater than .72V. This is the OVP protection. Please let me know if anything is unclear.

Best Regards,
Katelyn

Hello,

Please let me know condition for restart after stop by OVP.

Regards,
ACGUY

Hello,

The device should restart after the OVP condition is removed. This will occur when the voltage drops below .72V.

In order to test the OVP functionality, can you run the following test? Remove the FB resistors, verify that the device is switching near 100% duty cycle, connect the FB pin to 0.8V, then remove the 0.8V and verify the timing for start up?

Thank you,
Katelyn

Hello,

I will try your suggested work. Before on that,
"The device should restart after the OVP condition is removed. "
Therefore, restart sequence with OVP is
1) OV occur, Vfb over 0.72V,
2) OV is been remove, Vfb decline to 0.72V,
3) LM3150 stop to switching operation,
4) After a while LM3150 is restart.
Are they correct?

Regards,
ACGUY

Hello,

Please see the attached file.
LM3150 can't to OVP operation by once OV pulse on FB, the low side FET is be latch ON.
This device needs second OV pulse for normally OVP operation.
This symptom contradicts the explanation described in the data sheet, and I think it is a bug of the OVP operation.
Please specialist opinion.

Best regards,
ACGUY

Hello,

Thank you for sharing this waveform. Was this measurement also taken on an unmodified EVM?

Thank you,

Katelyn

Hello,

>> Was this measurement also taken on an unmodified EVM?

Yes. no changed and unmodified.

https://e2e.ti.com/support/power-management/f/196/t/792836
https://e2e.ti.com/support/power-management/f/196/t/808974

I chasing to this symptom long time. I never taken clear answer from E2E not yet.
This DC/DC is using for CPU board. When insertion USB, LM3150 output voltage line is received instant noise.
LM3150 is Low-FET ON, Low-FET pull the output charge, Vout drop, CPU will be reset. It has heavy impact.
However, LM3150 datasheet does not say that operation stop when OV.
I obtained the EVM from web market, tried OVP test.
I tested many time, I think that gate of Low FET is pulled to Vfb OV.
Please let me know your opinion.

Regards,
ACGUY

LM3150 OVP test.zip

Hello,

Thank you for sharing this additional background information.  

I am confused about the FB voltage in your original waveform.  The FB voltage goes to 0-V.  However, you mentioned that you only remove the FB signal, you do not ground this pin.  Can you confirm this again? I would expect the FB signal to return the 0.6V when the pulse is removed.  

I will also try to measure myself on the EVM next week.

Best Regards,

Katelyn

Hello Katelyn,

I inputted 0.8V to FB-port by mechanical switch. 

After remove the 0.8V OV signal, input OV signal is float, it is not 0V.

Regards,

ACGUY

Hello,

Thank you for your confirmation.

I tried the same test on the EVM.  I confirmed the similar behavior.  When 0.8V is applied to the FB pin, the output voltage will drop. After 0.8V is removed, the FB voltage goes to 0-V for 15-20ms.  Then, the device will enter start up.  This is expected behavior.

Please let me know if you have any remaining questions.

Best Regards,

Katelyn

Hello,

Thank you for your working for confirm.

About your comment "This is expected behavior.", I think it has inconsistency between with datasheet.

Question;

-Why does the LM3150 OVP behave differently than what is described in the data sheet?

-If TI thinks so it, why does not TI write it on the data sheet?

Regards,

ACGUY

Hello,

Thank you for reply. I accepted your suggestion.
By the way, are there any plans to revise the data sheet? and when is it?

Regards,
ACGUY