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Q: TPS62260, TPS62240, TPS62290, TPS62065: how to select inductor by 1838493
I was working with them through Switcher Pro and we tried to change VOUT conditions, 2.5V to 1.8V to 1V and load from 600mA to 230mA the inductor value stayed the same. Usually the inductor selection is based on 20%~40% ripple but with 2.2uH, at 1.8V, 230mA, this amounts to 72% ripple.
The main question is : how do we select the optimum inductance for these parts under different current loads? Based on our D/S it was difficult to select an optimum inductor, please see below:
The TPS62260 is designed to operate with inductors in the range of 1.5μH to 4.7μH and with output capacitors inthe range of 4.7μF to 22μF. The part is optimized for operation with a 2.2μH inductor and 10μF output capacitor.A: Re: TPS62260, TPS62240, TPS62290, TPS62065: by 1090425
In the TPS62xxx parts, the inductor value is not selected based on the ripple but based on the internal loop compensation and IC performance (efficiency, PFM mode, output ripple, transient response, etc.. These ICs support a relatively narrow range of inductance because of these reasons.
It is best to stick with the datasheet recommended/optimum LC output filter. This will give best performance and allows the same external LC to be used for all Vouts. Unless otherwise noted, this LC filter is recommended for all Vouts. Switcher Pro is coded to always pick the recommended LC filter, unless some user entered performance metric cannot be met with this filter.
Changing the LC filter affects many performance parameters. We have this app note for the TPS6206x that discusses some of these tradeoffs with an emphasis on stability: http://www.ti.com/lit/an/slva441/slva441.pdf
The same tradeoffs exist for the TPS62240/60/90 but no corresponding app note has been written.
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