TPS2493: [urgent] Adding External GATE-OUT Capacitance (datasheet P.26)

user6141161

Part Number: TPS2493
Other Parts Discussed in Thread: TPS1663,

Hi,

1. If I want to add ceramic capacitors across FET gate to source to measure against ESD, which should I add a resistance in gate side or source side?

2. How should I set the value of the resistance?

3. "Gate Capacitor (dV/dt) Control" can be effective way for ESD?Adding External GATE-OUT Capacitance.pptx

Best Regards,

Kasuga

over 5 years ago

0 Rakesh over 5 years ago

TI__Guru** 105361 points

Hi Kasuga,

We strongly recommend not to add any external capacitance between GATE and Source of the FET as it affects the stability of loop during current limit/ power limit modes of operation. As the behavior depends on several other parameters in the system (input cap, output cap, FET gm, GATE loop gain etc), the selection of resistor is not straight forward.

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Thank you for your reply.

I understand that the solution is not recommended.

I'm facing the short term Vout voltage drop caused by ESD test (above 10kV). Please see attached waveform.

When Vout drop continues about 15msec, FLT and PG show fault state but return normal state after that. This situation is OK because our system can restart correctly.

But when Vout drop continues about 2msec, both FLT and PG keep normal state but our system cannot restart even though Vout is supplied.

Do you know what is happen in those situations? I'd like to know how to resolve this issue.

About ESD issue.pptx

Best Regards,

Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

Can you add small filter (time constant of 500ns to 1us) across current sense amplifier and check. It should help to avoid shutdown during ESD event. Please refer app note http://www.ti.com/lit/an/slva703/slva703.pdf for the background.

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Thank you for the advise.

Is it correct that I should refer page 10-12?

Best Regards, Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

Correct.

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Please confirm the location where RC filter (1us time constant) is added in attached file.

Best Regards, Kasuga

RC filter.pptx

0 user6141161 over 5 years ago in reply to user6141161

Prodigy 150 points

Hi Rakesh,

I’m sorry to bother you again.

Would you like to check the schema and pattern? RC filter and TVS diode have not been added yet.

Please let me know if there are any concerns.

Best Regards, Kasuga

Schema and Pattern.pdf

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

If you are redesigning the board, I strongly recommend to use TPS1663. It solves all the challenges you are seeing with TPS2493

Please let me know. In case, you want to proceed with TPS2493, please send me filled up design calculator of TPS2493 for review.

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Thank you for your advice. But I don't have enough time to change controller IC from now. So please check design calculator of TPS2493.

TPS249x_8x_Design_Calculator_REV_B_20200122.xlsx

Regarding RC filter (0.1uF + 10ohm, 0.1uF + 5ohm), I tried to add as "RC filter.pptx " but Vout drop was occurred.

Do you have any other idea?

Best Regards, Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

Thanks for the details. The design looks good from SOA margin point of view.

The RC component connections across Rsense in your schematic are correct. To make it more effective move C close to VCC & SENSE pins. If this does not help, please consider adding more capacitance or LC filter at the input of the hot-swap.

Also, to suppress the transient voltages, a TVS diode (SMBJ33A) would be needed at the input. The blog explains why TVS diode is needed https://e2e.ti.com/blogs_/b/powerhouse/archive/2019/12/06/selecting-tvs-diodes-in-hot-swap-and-oring-applications

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Thank you very much for checking. I'm relieved to here that.

Regarding the placement of RC filter, I will try to move C close to VCC & SENSE pins.

>please consider adding more capacitance

Is there a guideline for the upper limit of the capacitance?

Regarding TVS diode, are there any concerns about using DFLT30A (Diodes Incorporated)? Does it have enough spec for me?

Max.Peak Pulse Current : 4.65A.

DC Steady-State Power Dissipation : 1W

Best Regards, Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

The limitation on the input capacitor value comes from the inrush currents during AC adapter plug-in. I suggest not to use more than 10uF at the input.

Regarding TVS diode, I recommend to use SMBJ30A to clamp effectively the inductive kick-back voltages during circuit breaker turn-off events as well as to absorb the transient events from the supply side.

Please refer https://e2e.ti.com/blogs_/b/powerhouse/archive/2019/12/06/selecting-tvs-diodes-in-hot-swap-and-oring-applications and https://www.powerelectronics.com/technologies/circuit-protection-ics/article/21853356/tvs-clamping-in-hotswap-circuits to get overview on the selection of the TVS diode.

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Thank you for your advises.

Unfortunately, currently I can choose only DFLT30A (Diodes Incorporated) or 1.5SMC43A (GOODARK ELECTRONICS).

Can I also use chip varistor instead of TVS diode? (e.g. EZJZ0V420WA / Panasonic)

Best Regards, Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

Yes, varistor can be used in place of TVS diode as it provides the same function. As the transient voltages depend on the value of the input path inductance, we suggest to test on actual hardware and decide on the TVS rating.

Best Regards, Rakesh

0 user6141161 over 5 years ago in reply to Rakesh

Prodigy 150 points

Hi Rakesh,

Currently I can see the effect during ESD test only when I add external capacitance between GATE and Source of the FET.

>We strongly recommend not to add any external capacitance between GATE and Source of the FET as it affects the stability of loop during current limit/ power limit modes of operation.

Would you please tell me in detail about the risk when adding external capacitance in my schema?

Best Regards, Kasuga

0 Rakesh over 5 years ago in reply to user6141161

TI__Guru** 105361 points

Hi Kasuga,

The additional capacitance introduces phase-shift in closed loop control modes of operation such as power limit or current limit which can lead to high frequency oscillations. These oscillations would keep the device in fault mode for elongated period than set at timer and stress the hot-swap FET.

Best Regards, Rakesh

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TPS2493: [urgent] Adding External GATE-OUT Capacitance (datasheet P.26)