# Buck boost converter + LDO or 2 Buck boost converter

I am currently designing a circuit where we have a lipo battery powering two rails:

• Rail 1: some RGB LED with 5V power supply
• Rail 2: a bluetooth chip with 3.3V power supply

• Option 1: use 2 buck boost converter to go up from [3V-4.2V] to 5V one side and to 3.3V on the other side

• Option 2: use 1 buck boost converter to go up to 5V creating rail 1, then use rail 1 + a LDO or DC-DC to go from 5V to 3.3V to create rail 2

What is it better to do and why?

On the other hand an LDO won't be as efficient as a buck-boost converter, but it all depends on the current demand of the bluetooth chip. I suppose we are talking about max 30 - 40 mA peak consumption here. That will be $\text{1.7 V} \times \text{40 mA} = \text{68 mW}$ wasted energy. And it is the peak, most of the time the bluetooth chip will draw much less. So I would definietly go with the second option.