LM25145: Does PGOOD work as OVP function?

Hung Ching Hsu

Part Number: LM25145

Hi Team

My customer is asking if LM25145 have OVP function to protect devices behind output of LM25145 when output of LM25145 is going to high.

It seems LM25145 have PGOOD function, which will disable PGOOD pin if FB is outside ±0.8% of Vref.

Does PGOOD function work as OVP function here?

Thanks.

Regards,

over 2 years ago

0 Timothy Hegarty over 2 years ago

TI__Mastermind 49597 points

Hi Jo,

Yes, PGOOD goes low when FB exceeds 108% of the nominal level (see the EC table in the LM25145 datasheet for more detail).

Regards,

Tim

0 Hung Ching Hsu over 2 years ago in reply to Timothy Hegarty

TI__Expert 3086 points

Hi Tim

Thanks for the reply.

I understood there is PGOOD function in LM25145.

Customer wants to know if LM25145 uses PGOOD signal to perform OVP inside this IC?

E.g, will LM25145 open high-side MOSFET or short low-side MOSFET to prevent high voltage output to devices after LM25145 when output voltage of LM25145 is going too high?

Customer is worrying that, even PGOOD is disabled when output voltage went too high, the high voltage will still output the device after LM25145 so the device after LM25145 may be damaged due to high voltage output of LM25145.

Or does customer need external IC for OVP function? If yes, could you recommend one?

Thanks.

Regards,

0 Timothy Hegarty over 2 years ago in reply to Hung Ching Hsu

TI__Mastermind 49597 points

Hi Jo,

The control loop will always respond to keep the output voltage at the programmed setpoint. So, for example, if Vout goes higher during a load-off transient, the lopp turns on the low-side FET to ramp down the inductor current, effectively reducing the output voltage overshoot. This is independent of the PGOOD signal. Most applications do not require an external OVP function.

Regards,

Tim

0 Hung Ching Hsu over 2 years ago in reply to Timothy Hegarty

TI__Expert 3086 points

Hi Tim

Thanks for the explanation. I understood. I'll share the info to customer.

BTW, is above description also inside datasheet? I looked it up but I couldn't find it.

Thanks.

Regards,
Jo

0 Timothy Hegarty over 2 years ago in reply to Hung Ching Hsu

TI__Mastermind 49597 points

Hi Jo,

It's probably not stated as explicitly as that in the datasheet.

Regards,

Tim

0 Hung Ching Hsu over 2 years ago in reply to Timothy Hegarty

TI__Expert 3086 points

Hi Tim

Thanks for the reply!

Customer wants to confirm that, will High-side FET keep OFF and Low-side FET keep ON if feedback voltage keep being higher than 108% of Vref?

Just want to make sure above protection won't stop so Vout won't go higher during this situation.

Thanks.

Regards,

0 Timothy Hegarty over 2 years ago in reply to Hung Ching Hsu

TI__Mastermind 49597 points

Hi Jo,

Yes, in that situation the loop responds to pull down the output voltage (by leaving the low-side FET on).

Regards,

Tim

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LM25145: Does PGOOD work as OVP function?