TPS54425: TPS54425 Switch node negative Spik

Kao Mick

Intellectual 350 points

Part Number: TPS54425

HI SIR

We use tps54425 to design 12V to 1.0V_4A, and measure the switch node negative Spike beyond the maximum value.

We have been very close to the ic body to measure this voltage waveform.

We want to confirm whether such a situation will cause damage?

Can we use RC snubber or TVS to suppress this phenomenon?

The equipment we use is as follows ~~
Tektronix P5205A-2 High Voltage Differential Probe 100MHz 50X Bandwidth no limit
Oscilloscope: Tektronix DPO5104B 1 GHz digital 4 ch Bandwidth: 1GHz

over 5 years ago

0 JohnTucker over 5 years ago

TI__Guru**** 191445 points

Kao,

That is barely measuring past -3 V. The most accurate measurement will require a differential probe. I think you will find that if you measure it properly with a differential probe, the negative excursion will be well within specification.

0 Kao Mick over 5 years ago in reply to JohnTucker

Intellectual 350 points

HI SIR

Would you recommend bootstrap to connect 0.1uF in series with 3.3 ohms?

0 Ryan Hu (BSR-MV) over 5 years ago in reply to Kao Mick

TI__Expert 4035 points

Kao,

Typically, a resistor in series with the bootstrap cap is used for the EMI improvement by slowing down the slew rate of the highside mosfet. Here you can use the 3.3 ohm resistor of course.

0 Kao Mick over 5 years ago in reply to Ryan Hu (BSR-MV)

Intellectual 350 points

HI SIR

I use this method to eliminate negative spikes, which can be improved.
I tried four methods to improve:
Vin pin in parallel with a 1nF capacitor.
Vin to 12V connects a Ferrite bead 120ohm in serial
RC Subber.
bootstrap series resistance 3.3ohm.

0 Ryan Hu (BSR-MV) over 5 years ago in reply to Kao Mick

TI__Expert 4035 points

Hi Kao,

Both of the above methods are useful as long as the solution cost is acceptable for your customer.

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Power management forum

TPS54425: TPS54425 Switch node negative Spik