LM27402: Chip failure at hot swap

PRABHAT RANJAN TRIPATHI

Part Number: LM27402

Dear TI team

I used an LM27402SQ/NOPB to design my buck converter and faced a weird problem which I shared here

(e2e.ti.com/.../lm27402-how-much-current-can-vin-pin-handle

At that time I was told that the problem may have arisen due to the voltage at the Vin pin would have exceeded the absolute max rating of 22V, so I modified the circuit and added a TVS diode.

I used the circuit again with the new LM27402 IC, this time I captured the voltage at Vin pin in a DSO. This time the peak voltage at the hot plug reached only 21.1 Volt but the device still failed.

Do let me know what should be done now. I am attaching the screenshot of the hotplug event,

over 3 years ago

0 Ryan Chen over 3 years ago

TI__Genius 15187 points

Hi Prabhat,

Can you share a schematic of the circuit, an image of the PCB layout, and where the measurements are being made on the layout?

Best,

Ryan

0 PRABHAT RANJAN TRIPATHI over 3 years ago in reply to Ryan Chen

Expert 1102 points

Can you share your email id?

0 Ryan Chen over 3 years ago in reply to PRABHAT RANJAN TRIPATHI

TI__Genius 15187 points

Hi Prabhat,

I sent a friend request on E2E. Once accepted, a private message can be sent with attachments.

What is the part number of the added TVS diode?
Do you have an oscilloscope plot of the hot plug voltage with and without TVS installed?

I would expect the voltage to clamp and be flat somewhere on the hot plug voltage waveform.

Where you measuring the waveform? Tip and barrel or a differential probe should be used to measure the voltage of the IC VIN and GND pins.

See Figure 3 in Using the TPS40192EVM-525 (ti.com) for a demonstration of the tip and barrel technique.

Best,

Ryan

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LM27402: Chip failure at hot swap