TPS54821: TPS54821 IC has no short circuit protection

EngHW

Part Number: TPS54821
Other Parts Discussed in Thread: TPS54202

Hi,

I am using TPS54821 IC to step down +12VDC Voltage to +5V, the IC perform well for high current, has very low drop and produce very less Heat. But It has no short circuit protection if I accidentally connect output to ground IC is getting damaged. How can i solve this?

Is there any short circuit protection circuit? which has to be faster then damaging of ic.

Data sheet says IC has Hiccup protection !!

Thanks and Regards,

Surjit

over 8 years ago

0 Luke Pan over 8 years ago

TI__Intellectual 2790 points

Could you share us the schematic and layout screen shots. And how did you short the Vout to ground?

0 EngHW over 8 years ago in reply to Luke Pan

Prodigy 195 points

Hi,

Please see the picture. Input is 12V and Output I set to 11V. I have a 3.5mm jack at the Output but when I plug in the connector, there is a short from TP2 to ground. Ans this distroy the IC (Lower side mosfet).

0 Luke Pan over 8 years ago in reply to EngHW

TI__Intellectual 2790 points

TPS54821 has short protection. I guess it's because when the device is shorted, there will be large current flow through the input, if the VIN is not bypassed well, the self-inductance of the PCB trace will lead to large ringing spike at VIN, which will result in the VIN voltage over the absolute max VIN spec, and destroy the device. could you provide the layout? And could you capture the VIN, PH waveforms during the short?

0 EngHW over 8 years ago in reply to Luke Pan

Prodigy 195 points

Hi Luke,

Thank you for your reply. I will try to send you waveform because its difficult to replace QFN package. I have destroyed around 5-6 ICs in this situation. Please see the layout. I have some filters before the VIN. Should I increase the L403 from 3.3uH to 10uH? When I make short Its for a very short time and Lower MOSFET (between PH and GND) is getting damaged and High MOSFET is still working (VIN to PH)..

0 EngHW over 8 years ago in reply to EngHW

Prodigy 195 points

Or there is also other possiblity as described here, My Switching frequency is around 800kHz with 52.3kOhm resistor. According to equation given below this could be a problem.

0 Luke Pan over 8 years ago in reply to EngHW

TI__Intellectual 2790 points

TPS54821 employs low side current limit to prevent current 'run away'. the document you mention here is for those device don't employs this technology, if the device only employes cycle by cycle current limit, and when the device hit Ton_min during short, the current will run away, but TPS54821 won't.

For the layout, the C403 and C404 should be close to PVIN and GND, so suggest to retate C403 and C404 by 180 degree. For so large power application, the PCB layout is very critical, pls follow the layout example in the datasheet.

0 Luke Pan over 8 years ago in reply to Luke Pan

TI__Intellectual 2790 points

Also L402 will oscillate with C403 and C404 at such condition, so suggest add a bulk capacitor (47uF or higher) parallel with C403 and C404.

0 EngHW over 8 years ago in reply to Luke Pan

Prodigy 195 points

Hi Luke,

Thank you for correcting, I will update the Layout and C403, C404 Values. Please see waveform in normal working condition, PH and VIN. I have observed some ringing. Input is +12V, expected Ourput +11V.

0 Luke Pan over 8 years ago in reply to EngHW

TI__Intellectual 2790 points

you can set full band width, set VIN as the triger channel, trigger point 14V, press 'Single', then short the VOUT, to capture the ringing spike.

0 EngHW over 8 years ago in reply to Luke Pan

Prodigy 195 points

Hi Luke,

I have just got this waveform and perform short test now. How to reduce this ringing? what could be the source?

0 Luke Pan over 8 years ago in reply to EngHW

TI__Intellectual 2790 points

Could you also probe the VIN waveform while you do the short test? Put C403 and C404 close to PVIN and GND pin (need to change the layout). Below is an application note about layout. Also suggest to put more cap parallel with C403 and C404.
www.ti.com/.../slpa005.pdf

0 EngHW over 8 years ago in reply to Luke Pan

Prodigy 195 points

Hi,

Sure I will make those changes, one question my current requirement is very low ranging from mA to 1A max (full load). I have chosen 3.3uH inductor. could it be a problem?

0 Luke Pan over 8 years ago in reply to EngHW

TI__Intellectual 2790 points

What's the part number of your inductor? How large is the rated current and saturation current? For 1A max load, this device is over spec too much. TPS54202 is more suitable device for such application, SOT-6, easy of use.

0 Neal Zhang over 8 years ago in reply to EngHW

TI__Expert 4720 points

Hi Surjitsinh,
This ring is also caused by the layout. If you put C403 and C404 closer to the IC the ring should be smaller. Also you can use snubber. Please look at this article for further reference: "www.ti.com/.../slyt465.pdf"

Power management

Power management forum

TPS54821: TPS54821 IC has no short circuit protection