LM5175: LM5175 USB typC PD with TPS65987

Ali Tatari38

Part Number: LM5175
Other Parts Discussed in Thread: TPS65987, ,

We are in the process of brining up the board overseas as I write this email so it is critical if you can get back to us asap. We have TPS65987 USB type-C controller programmed in Source/DFP mode. We are following the reference design for TPS65987using LM5175 as source for VBUS connected to PP_HV2 of TPS65987. We has simulated the LM5175 design on Webench and bias is 5V instead of 9V as suggested by Webench simulation. The problem we are seeing is that USB Type-C takes some time to negotiate PD contract and at times it keeps trying but never negotiates the contract. Even when it does negotiate PD contract it charges the devices connected at very low current like 60 mA – the max it goes upto is like 400 mA.

We have isolated the problem to LM5175 by disconnecting it from the circuit and providing 5V externally from benchtop supply. The system works fine and right away negotiates PD contract and starts charging devices connected at 5V 1.A to 1.2A range.

I can't attach schematic in this forum - PSIL060A(001)_Sch.PDF LM5175_simulation.pdfdifference from simulation results is LM5175 is in DCM mode by grounding mode pin. We also have ADCIN1 set to 100K to GND . I am attaching LM5175 Webench simulation and TPS65987 reference design. This is of high urgency as we are overseas and I would appreciate a quick feedback.LM5175_simulation.pdf PSIL060A(001)_Sch.PDF

over 6 years ago

0 Youhao Xi over 6 years ago

TI__Guru* 78240 points

Hi Ali,

It sounds like a power sequence issue. Can yo enable the LM5175 first, then turn on the USB controller? If the LM5175 power up time appears to to be long, you can reduce the SS capacitor value to get a faster speed.

Thanks,
Youhao Xi, Applications Engineering

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

Hi Youhao,

LM5175 is always on in our design. The enable is tied to VIn all the time . TPS65987 is also always enabled . What mode should we be in DCM ot CCM. Currently we are in DCM mode.

Regards,

Ali

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

If the circuit is always on, the LM5175 output should has established output voltage, no matter it is in DCM or CCM. Can you confirm that the output voltage of 5V is already there before the USB negotiating? If yes, we may have to contact the designer of the ref design circuit.

Thanks,
Youhao

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

Yes 5v output is up before usb is plugged in based on PD negotation 5V ,9V or 12 V is selected just as reference design for TPS65987 EVM

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

Does the ref design pass the negotiation successfully, or also has the problem?

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

Yes but it is buck and doesn't have LM5175

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

I see. We also have a reference design with the LM5175 published at the following link

www.ti.com/.../PMP20774

The USB controller is a different one. I mentioned this because it I am afraid it is not the LM5175 itself causing the negotiation problem. Let me consult our TPS65987 expert. Stay tuned. This may take a few days given it's already Friday afternoon.

If you wish, you can create a new post, under the subject of TPS65987, and mentioned that the LM5175 has already supplying the 5V, but the TPS part failed the negotiation? The engineer supporting the TPS65987 may shed some lights on this. This way you may get answer earlier than I do.

Thanks
Youhao

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

Any update?

0 Ali Tatari38 over 6 years ago in reply to Ali Tatari38

Intellectual 470 points

Another observation we have seen is that when system reset (VIN =4.3V) we will see LM5175 turns on the fet incorrectly and cause low side fet for boost to be burnt. Vin goes to 0 and then goes back to 4.3V

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

Hi Ali,

I have updated you in your other thread, regarding the info I got from our TPS65987 expert. Please check that one.

Do you have a scope picture showing the incorrect turn on of the low side FET when Vin drops below 4.3V? Do you have blocking diode at the VIN pin to prevent the VCC from being discharged through the internal LDO body diode when VIN pin drops?

Thanks,

Youhao

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

I will get you scope images but how we know is that we measure Vout of LM5175 and it is not 5V anymore . it is around 4.5V with no load. This happens after when main 4.3V resets.

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

I measure the Feedback to be at 0.734V which is out of range for LM5175

0 Ali Tatari38 over 6 years ago in reply to Ali Tatari38

Intellectual 470 points

also PGOOD is pulled low

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

This implies that the LM5175 output is not fully established. Something pulls the Vout low.

0 Youhao Xi over 6 years ago in reply to Youhao Xi

TI__Guru* 78240 points

Hi Ali,

May I assume the issue is resolved and we can close this thread here? You can always reopen it by following a new post.

Thanks,
Youhao

0 Ali Tatari38 over 6 years ago in reply to Youhao Xi

Intellectual 470 points

Hi Youhao,
you can close the ticket as it might be important for you . I am going to ask again - can you please suggest another cross FET to CSD17571 with better Qg? Does Rdson have anything to do with this issue? if yes then can you please explain.

0 Youhao Xi over 6 years ago in reply to Ali Tatari38

TI__Guru* 78240 points

Hi Ali,

It is not appropriate for me to openly recommend a competition's part on e2e. May I suggest you to refer to the LM5175EVM's FET selection?

www.ti.com/.../snvu440a.pdf

Thanks,
Youhao

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LM5175: LM5175 USB typC PD with TPS65987