Undershoot of TPS61087

takahiko yokota

Other Parts Discussed in Thread: TPS61087

My customer evaluates TPS61087 using EVM under the following conditions.
But switching voltage's undershoot is -0.82V, so the value is over the Absolute Maximum Ratings of this device.
Could they use it this condition?
If it is bad, could you tell me the solutions?

Conditions

Vin=4.1V

Vout=5V

Iout=No Load

fsw=1.2MHz

Best regards,

Yokota

over 9 years ago

0 Helen chen over 9 years ago

TI__Mastermind 40080 points

Hi,

-0.3v on the datasheet is just refer to the DC current. If the -0.82V voltage duratoin is very short, then it is OK.

Could you attached the waveform?

0 takahiko yokota over 9 years ago in reply to Helen chen

Mastermind 7135 points

I attached the waveform.

Green is output voltage, pink is swiching voltage.

TPS61087.pdf

Best regards,

Yokota

0 Helen chen over 9 years ago in reply to takahiko yokota

TI__Mastermind 40080 points

It is OK. No problem.

And how they measure it? Because if the measure point has some distance to the SW and its nearest return, then the SW negative spike will bigger than the real spike.

0 takahiko yokota over 9 years ago in reply to Helen chen

Mastermind 7135 points

Thank you for the answer.

But I'm sorry my customer doesn't have another waveform.

I have two question in addition.

1. You said if -0.82V is AC voltage, there are no problem over absolute maxim ratings during short time.

Are there clear criterions such as the voltage, the time, etc?

2. If there are theclear criterions, are another devises except TPS61087 same it?

Best regards,

Yokota

0 Helen chen over 9 years ago in reply to takahiko yokota

TI__Mastermind 40080 points

Yokota-san,

No, we have no spec. Because actually this negative voltage spike is not directly added on the IC's internal MOSFET. As the spike is cause by the parasitic parameter, so this voltage also related to the layout. So this voltage is a total series voltage of the PCB wire, internal bonding wire, and the internal MOSFET. so only small ammount of the spike is added on the MOSFET. generally, a -1V, 20ns spike is sure to be OK.

Power management

Power management forum

Undershoot of TPS61087