Yes, I have gone a bit over the top. For a given application the 34063 will do the job but it has its limitations.
The UCC380X IC itself is just a controller. What you place around it will determine the available power and efficiency and the example you have found is designed to achieve a certain function which in itself is low power.
Let's say you want to go from 9V to 24V and assume you expect the battery voltage at end of life to have dropped to 6V then assume you want a maximum output current of 0.5A If you ignore voltage drops and losses to begin with then you want 12W output power which will require an average current from your 6V source of 2A. Pick a switching frequency... 100KHz, higher frequency means more switching losses in the mosfet and diode due to parasitic capacitance and reverse recovery but it is a design trade off.
The duty cycle is D = [VOUT - VIN]/VOUT or 0.75 giving a switch on time of 7.5uS. A general starting point is to accept 20% ripple current in the inductor which would be 0.4A from that your inductor value would be L = VIN.TON/dI or 112uH call it 100uH and the ripple becomes 0.45A. The peak inductor/switch current will be 2.225A, average plus half ripple. For the switch treating it as a simple rectangular wave and ignoring the ripple then it's RMS will be 2*SQRT[D] or 1.73A.
Let's say you are happy to lose 0.5W in the mosfet and pretend half that will be switching losses with the other half being conduction losses. You would need a device with an RDSon of .25/1.73^2 or 0.084R or 85mR and be capable of being driven by a 5V gate drive signal . It would need a VDS rating in excess of 24V, plus one diode drop, so use a 30V device... IRLR2703 seems to fit the bill.
http://www.irf.com/product-info/datasheets/data/irlr2703pbf.pdf
You will need a fast diode and it will see peak currents of 2.25A, and some extra for possible transient overload. Its average current will be... simply the output current and its reverse voltage the output voltage. Something like a BYV27-50 will be more than up to the task,
**broken link removed**
You will need a current sense resistor in the source of your Mosfet. Now peak limit in the UCC380X is relatively high at 1V for low voltage supply operation. I might only assume that it has been made that way for compatibility with the older UC384X range. Pick a 0R1 sense resistor value and you will lose 300mW to generate a peak signal of 225mV.
The circuit will need slope compensation and in addition you can use the IC's reference to offset things further in order to match the 1V if required.
So far ignoring other switching losses we have 0.5W mosfet, 0.3W sense resistor. The diode will add about another 0.5W and I'll ignore the other contributions. Total is 1.3W for 12W out so efficiency is about 90%.
Jumping into LTSpice,
Linear Technology - Design Simulation and Device Models
This is not an exact representation since the suggested components are not available in the package.. it does show the basic set up though.
The LT1243 is 'similar' to the UCC3803.
Q1, D2 and R5 supply the slope compensation. During switch off time the current downslope is 18V/100u converted to a voltage of 18,000 in the sense resistor. Half that is 9K. In the LT1243 the ramp amplitude is 1.7V and with Fs at 100K we get 170K so we have to attenuate it by about 20 giving a value for R5 of 20K. R10 offsets the signal to match the internal 1V peak limit of the IC.
Apart from the compensation the rest is more or less as previously described. I'm afraid I've been evil and 'guessed' at values in the feedback network to get something that 'works'.
Start Up,
In regulation,
Output power is 11.93W. Input power is 12.73W. Losses are 0.8W, better than expected but the diode is a Schottky and the Mosfet is specced with a lower RDSon, 93% efficient. Depending on the models LTSpice might underestimate some of the switching losses.
Model attached.
Genome.