Any suggestions for a 5V/500mA boost regulator that I can use instead?
But since I draw maximum 250mA@5V I thought the inductor I use would be good enough?
250mA should be fine.
The data sheet wants you to use a inductor of 1A or more and you did that.
If I could work on your supply for a couple of minutes I would know more.
Pictures below:
Fig 7. Normal operation for a PWM. The bottom trace, current ramps up when the switch is closed, and ramps down when current goes to the load. Notice the output ripple. While the inductor current is sloping down power is going to charge up the output capacitors. The majority of the time the capacitors are discharging.
Fig 8 & 9: Notice the "time" is different 5uS/10uS/20uS
This IC gets into a mode where it adds several cycles to make one. Fig 8 Here 4 or 3 cycles are together. In Fig 9 There are approximately 12 cycles added together. This produces audio noise.
Fig 10:
There is no description, but I believe they increased the inductance to get this to happen. The current trace is 200mA/div in Fig 10 and the slope of the current is much less indicating more inductance.
Things to try:
1)Try two of your inductors in series to double the inductance. This might push you into Fig 10. Hopefully getting you a higher frequency.
2)A saturating inductor often "sings". That is why I first jumped to that thought. If you get new inductors I would look at 1.5A parts just to be safe. The current limit for the IC is 1A +/- some amount. Note: the average current is much less than the peak current. In Fig7 the peak current is 350mA. The output current is (a ramp that starts at 350 and ramps down to 0), (The average of a 350 mA ramp is 175mA) and ( the output is only happening 1/3 the time so 1/3 of 175mA is 58mA) In
this mode it takes 350mA peak to get 58mA of load current.