3.3Vin 1-15Vout

[kcs]

I am looking for a solution how to get adjustable voltage by 1V increments in a range of 1 to 15V that is going to be done with a microcontroller.

Requirements:
 - Vin = 3.3Vdc
 - Vout = 1-15Vdc
 - Isw = 20mA
 - Iq <= 2mA
 - Efficiency >= 50%

I was searching for step-up/step-down DC-DC converter with I2C control. However, could not find anything that matches my requirements. So, I am thinking of doing the following:
1. Use fixed step-up DC-DC converter to get ~18V from 3.3V
2. Use adjustable step-down DC-DC converter to be able to get 1-15V out of 18V
3. Use digital potentiometer that is controlled over I2C

Is there any more elegant solution that anyone could recommend me? And by "elegant" I mean something that has better efficiency, less external components and is less complicated.

[wraper]

Is there any more elegant solution that anyone could recommend me? And by "elegant" I mean something that has better efficiency, less external components and is less complicated.

Sepic converter http://www.ti.com/lit/an/snva168e/snva168e.pdf