LM5175: Feedback pin open OVP protection

Mike Yu

Part Number: LM5175

Hi Team,

The customer is testing the FB resister open protection. The vout will rise up to 54V. Is this the except behavior of our device?

As I know, the OVP of this device is sensing the feedback pin voltage. If the resister between FB pin and vout pin is opened, how did our device stop the PWM signal? Thank you.

The customer application condition and the FB OVP pin waveform are below.

Vin: 12~24V, Vout: 12V

Best regards,

Mike

over 3 years ago

0 Brigitte over 3 years ago

TI__Guru 58215 points

Hello Mike,

The OVP on the FB pin does not work when the top resistor of the feedback divider is removed. The FB pin voltage is then always GND independent of the output voltage.

I expect that the device is detecting the voltage on the VOSNS pin, but need to clarify the details.

0 Brigitte over 3 years ago in reply to Brigitte

TI__Guru 58215 points

Hello Mike,

As expected, the VOSNS pin will sense the output voltage. Does this clarify your question?

0 Mike Yu over 3 years ago in reply to Brigitte

TI__Intellectual 1830 points

Hi Brigitte,

Yes, just only want to clarify the VOSNS pin will sense the output voltage. Thank you.

Best regards,

Mike

0 Brigitte over 3 years ago in reply to Mike Yu

TI__Guru 58215 points

Hello Mike,

VOSNS does sense the output voltage for the slope compensation signal. It will not stop the output voltage from rising. Would you please measure the output voltage, the slope compensation voltage as well as SW2?

0 Mike Yu over 3 years ago in reply to Brigitte

TI__Intellectual 1830 points

Hi Brigitte,

After checking with the customer, due to our device only support OVP with sensing feedback pin, they try to test the OVP with pulling Vout up to OVP point. Thank you.

Best regards,

Mike

0 Brigitte over 3 years ago in reply to Mike Yu

TI__Guru 58215 points

Hello Mike,

If you want to make sure that even with a top resistor open, the system does not create too high voltage, you might use 2 resistors in parallel instead of a single resistor.

Power management

Power management forum

LM5175: Feedback pin open OVP protection