Hello,
LT3494 specifies the device can be operated from 2.3V to 16V, or, operating the device with 12V affects the internal voltage reference, and so output voltage : I wanted 18V, I get 36V! Vfb is measured 2,45V instead of 1,225V, with a set resistor of 2.49 MOhm.
I developped a circuit prototype for a project and assembled 3 boards. The problem is the same on 3 boards.
The input power supply is 12V typical (an eFuse protects the board against under voltage and over voltage : 11V to 13V) and I needed a low current 18V rail to supply a single opamp, so I found the LT3494. In the datasheet, all characteristics are shown for Vcc = 3V, BUT in the specifications, the device can be operated from 2,3V to 16V, so 12V is within the range. Input voltage isn't referenced anywhere regarding output voltage.
The only equation for output voltage is related to set resistor only, not input voltage.
Now, my problem is the device outputs 36V, FB pin voltage is 2,45V instead of 1,225V, and I don't understand why! If I lower the input voltage to 11V (the minimum the eFuse accepts), I get 32V output... So internal reference is not regulated at all.
In my case, CTRL pin is tied to 12V, the condition for CTRL > 1.5V is met. Set resistor is 2.49 MOhm according to the table p.10. Inductor value is 4.7 µH, calculated with equation p.7 (Vin = 12V, Vout = 18V).
Here are the schematics and the PCB layout :
