Setting Vmax of AP3032 LED driver?

[Pugbutt]

Hi Everybody.

I'm wanting to use a Diodes Incorporated AP3032 LED driver in a design.  (http://www.diodes.com/_files/datasheets/AP3032.pdf)   The datasheet says that, by default, you can just hook the OV pin to the output to set the max voltage to 27V.  The example schematic though shows a voltage divider there though, and the resistors are unlabeled.  This implies a variable setting to me, but there is no more detail given.

A similar (but much more expensive) part is a Linear Technology LT1618.  (http://cds.linear.com/docs/en/datasheet/1618fas.pdf)   They have a pin serving the exact same function, and they were nice enough to specify the relation between divider ratio and cutoff voltage.

Does anyone see how I can set a specific cutoff voltage on the AP3032?  27V feels way too high for my application. I'd rather set ~5V.

Thanks,
Craig

[michaeliv]

If you connect the OV to the output and get 27V, any voltage divider will only increase the maximum voltage.
I guess the only way to know for sure is to see what happens if you connect OV to output directly.
A work-around is to trick the current feedback with a resistor divider and a extra schottky diode, like attached. You do the math for the resistors .

[Kilrah]

27V feels way too high for my application. I'd rather set ~5V.

You're probably looking at the wrong chip then - as mentioned in the datasheet this one is specifically intended for driving 7 white LEDs in series, so around 20-25V output.