LT1615 feedbace pin going greater than Vin

Hi,

When the output is high, the FB pin will sit at about 1.24V. If the output voltage is drops, the FB pin can only drop as Vout drops.

Please send a schematic and/or explain how it is the FB will be higher than the input.

The input voltage is 3.8V.  The output voltage is adjustable between 4V and 20V.  If the output is at 20V, and then is switched to 4V, the fb pin will momentarily be above the supply voltage.  We do not want to have to monitor the output voltage and gradually adjust it down to keep the fb voltage below the supply.

thanks

Danny

Please explain how you intend to instantly change the FB divider to program the output. I understand you will be changing the resistor value, but, I want to know if you will be using a switch, and if so, let me know the speed of the switch.

Also, again, please send the schematic so I can see the total output capacitance, and let me know what the load current is during this voltage change.

Happy New Year!

On second thought, if you know the FB pin will exceed the input voltage when changing the output, you need to clamp it or take some corrective measures.

Regards.