I'm designing a solenoid powering and control device which is centered around the LTC3862-2 Step Up controller (see datasheet). I have taken as a design start point the typical application shown in page 38 of the datasheet. I have only modified the resistor divider values in order to get a 40 V output (316 kOhm and 10kOhm) instead of the 80V shown in this typical application.
My requirements are:
- Vin= from 6 to 8.4 Volts
- Vout= 40 Volts
- Iout= 2.5 Amps
Plus, the basic circuit schematic is shown below:
The problem comes when I activate the solenoid. Instead of having the 40V/2.5A from the step up, there is a sudden decline from the moment M1 closes from 40V to 24V, plus the current is only about 1.5A. As a result, the solenoid is far from moving the mechanism it is meant to. When the load is not connected, the output is stable at 40V.
Additionally these are other measures from the experiment:
- Battery voltage under load= 8.3V @ 5.5A (LiPo battery can deliver more than 30 A continuously).
- M1 transistor source(GND) to gate voltage 4.8V (transistor datasheet)
Do you know what is happening or the reason of this behavior? Can you think of a solution to avoid this output voltage drop?
Any help is very much appreciated. Thank you in advance!
From this schematic, I have only made this minor modifications:
- Changed output caps to 100uF 63V since output voltage for this application is 40V.
- Input capacitors changed from 50 to 16V since input voltage range is 6-8.4V.
- Resistor divider to FB pin in order to have 40V output (12.4 kOhm to 10 kOhm and 796 kOhm to 316 kOhm).
This results in this schematic:
Hope this sheds more light. Thank you very much!