TPS62090: Protection for SW pin

Hi Kato,

thank you for your question.

I wouldn't advise you to put a zener diode on the SW node. A diode would introduce additional losses, due to leakage current and parasitic capacitance. Moreover, its threshold could vary with the temperature, resulting in an even higher power dissipation.

If you  need to reduce the voltage spikes on the SW node, you could instead introduce a RC snubber between SW and GND.

Please ask again if you have any more questions.

Thanks,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml)

Hi Kato-san,

thanks for your answer.

It's difficult to give you any valid values for the RC , since they are strongly dependent on the ringing frequency of the SW node, again related to layout and parasitics.

You could refer at the application note Minimizing Ringing at the Switch Node of a Boost Converter (ti.com)
for designing your optimal snubber (the application note refers to a Boost example, but the main guidelines are valid also for a Buck).

In order to improve noise resistance, the main idea is to properly tune the value of feedback resistors (lower values usually lead to higher noise rejections, see Design considerations for a resistive feedback divider in a DC/DC converter, Noise Sensitivity section).
Moreover, it is important to focus on a proper layout (see Five steps to a great PCB layout for a step-down converter (ti.com)), both of the Buck converter and of any interfering noise sources.

Thank you, and please ask again if you have any more questions,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml)

Hi Kato-san,

Thanks again for your question.

Before putting a zener diode on the output you should keep in mind that you would have additional losses (diode leakage current) and you should pay attention to choose a zener diode with a threshold significantly higher than the output voltage (also considering its variation as a function of the temperature); in particular during Power Save Mode Operation the output ripple could be no more negligible and turn on the zener diode. 

If you don't have particular design constraints that could cause significant voltage surges, a zener diode with the previous specification could be almost useless.

One alternative could be to optimize the converter transient response.

I leave you as reference: Optimizing the TPS62090 Output Filter

Thank you, and please ask again if you have any more questions,

Stefano

All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml)