TPS54325-Q1 VREG and Soft-Start

Richard Elmquist

Other Parts Discussed in Thread: TPS54325-Q1, TPS54325

I have a customer who is asking a question on the ramp up of the VREG5 circuit in the TPS54325-Q1.

The block diagram seems to indicate that VREG is supplied directly from VCC. But is the ramp up of VREG5 affected by the soft-start circuit? The customer seems to think that VREG5 does not ramp up until the soft-start time is completed. Is this the way the circuit works internally or does it ramp up independent of the soft-start circuit? This is what seems to be implied in the block diagram of the part, but VREG5 is not very well explained in the data sheet.

The customer has said that they see VREG5 only ramp up after the soft-start circuit is finished. Please let me know if this is how the circuit operates or if it simply ramps up once Vcc is applied.

Thanks for your help with this!

Richard Elmquist

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

I'm not sure about all the exact timing, but I can tell you for sure that their assumption is not correct. The UVLO is tied directly to VREG5, not VIN. SS will not start until VREG5 is above the UVLO.

0 Richard Elmquist over 7 years ago in reply to JohnTucker

TI__Mastermind 45250 points

John,

Can you verify if VREG ramps completely regardless of the state of SS? Is it independent? The customer states that VREG seems to only finish ramping after the SS circuit completes. Is this correct? They are using VREG to pullup the PG signal and need to know whether there is a relation to SS or not. Is this something that you can answer?

Thanks for your help with this!

Richard Elmquist

0 JohnTucker over 7 years ago in reply to Richard Elmquist

TI__Guru**** 191445 points

I was working from memory on this. I no longer support TPS54325 and do not have any boards to check. I'll alert the MCP team.

0 Anthony Lang over 7 years ago in reply to Richard Elmquist

TI__Expert 4875 points

Hi Richard,

This is Anthony from TI MCP team. I will set up a test for VREG5 ramp up. I will get EVM baord tomorrow and I will get back to you as soon as possible.

Regards,

Anthony

0 Richard Elmquist over 7 years ago in reply to Anthony Lang

TI__Mastermind 45250 points

Anthony,

Sounds great!

Please let me know what you see in your testing.

Thanks again.

Richard Elmquist

0 Anthony Lang over 7 years ago in reply to Richard Elmquist

TI__Expert 4875 points

Hi RIchard,

The above is the scope waveform I saw in the lab. Yellow is EN. Purple is VREG5 and green is SS. The power on sequence of TPS54325 is Vcc-VREG5-SS.

Best regards,

Anthony

0 JohnTucker over 7 years ago in reply to Anthony Lang

TI__Guru**** 191445 points

That is what I recalled also, When EN goes high, VREG5 immediately ramps up, then SS begins after VREG5 reaches the UVLO point.

0 Richard Elmquist over 7 years ago in reply to JohnTucker

TI__Mastermind 45250 points

Anthony and John,

Thanks so much for your quick response!

I will let you know if the customer has any further questions.

Thanks again.

Richard Elmquist

Power management

Power management forum

TPS54325-Q1 VREG and Soft-Start