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TPS62170 Ripple Current and Power Save Mode Current Calculations

Luis Cordova
Intellectual 1940 points
Other Parts Discussed in Thread: TPS62170

Hello,

I am designing a power supply for a small module that will either be off or transmitting data. The typical current consumption per rail is around 300mA for each, a 1.8V and 2.8V rail. The 2.8V rail feeds the 1.8V supply from a 9Vnom supply (up to 14.5V max). Both of these devices are TPS62170s. I plan to use a 3.3uH inductor which has an inductance of around 2.3uH at the load current according to the datasheets Inductance vs. DC Bias Characteristics graph.

One big problem I am trying to avoid is switching in the AM band when or if the loading is light (Power Save Mode), which I do not anticipate it will be or should be. The calculations showed good numbers, but they were still a bit close for my taste, specifically on the wider VIN 2.8V switcher. I got 187.5mA is the PSM mode load current for the TPS62170 stepping down the 9V to 2.8V. Is this a safe amount of headroom given the typical load current is 300mA?

If not, I plan to increase the inductor size to the next size up, 4.7uH, which has an inductance of around 3.5uH at that load current.

Please let me know if this is a safe amount of headroom.

Thanks,

Luis

  • 0
    TI__Guru**** 150950 points
    300 mA compared to 187.5 mA is plenty of room in my opinion. You can always increase the inductance further if there is an issue.

    Both of the mentioned inductors seem to saturate more than usual, so picking a 'better' inductor with less saturation would also help.

    You should always confirm the circuit on an EVM to make sure it operates as you need it to.