I have a Li-Po battery which has a discharge voltage range of (2.5-4.2)V and I want a regulator which is able to convert this voltage to 3.3V. I was told to use a buck boost converter. I have found one which is a buck boost converter and the other a buck converter. Reading the descriptions of both, I think both will work but I would like to ask for your opinions or if you have any other recommendations of components that'll work. Here below are the datasheets of each component:
The maximum output voltage of a buck converter is slightly lower than the input voltage. Therefore if you use the buck design, you won't get 3.3 V output when your battery voltage drops below 3.4 V or so.
This behavior isn't really explicitly mentioned in the datasheet (except where they call the chip a "step-down" converter), because it's such a fundamental limitation of buck converters that people using them are expected to know about it.
There is one section that does at least allude to the limitation:
If you use only a buck, you can explore the option of re-specifying your 3.3V rail to be a lower voltage, say, 2.7V. Then choose a buck that has an LDO mode (100% duty with linear voltage regulation) that kicks in when the battery is close to the target voltage.
Otherwise, you need to use buck-boost.
And, you should not drain the battery all the way down to 2.5V, it will damage it. More here: https://batteryuniversity.com/learn/article/confusion_with_voltages
Buck-boost integrated with charge / discharge control is available as a single IC from the usual places (TI, Maxim, Analog Devices, etc.) Worth a look.