I am facing a serious issue in my TPS40210DGQR Boost circuit. Please find the attached schematic.
In the Schematic the TPS40210DGQR (U20) Boost converts the battery voltage 12V to 45V. The 45V is used to 2 purpose. The 1st purpose is close back a big magnetic solenoid and to fire a small solenoid. In 2nd purpose this 45V is buck converted to 18V using Buck Converter IC TPS54160DGQ (U6). The 18V is used to generate 5V using TPS54226PWP DC/DC Converter (not included in attached schematic) used for digital circuit with maximum load of 300mA. Also this 18V is used to generate 3.3V using TPS715A33DRVR LDO (not included in attached schematic) for powering the Microcontroller (MSP430F5438A).
The circuit operation is that when microcontroller turns on the CHARGE_45V signal the battery voltage is connected to the Boost Converter. The Boost Converter should boost convert the battery voltage to 45V and charge the C36 (2200uF) Capacitor. Also this 45V is connected to Buck Converter which converts this voltage to 18V and then 18V is further converter to a 5V and 3.3V. The Micro controller will switch off battery power to Boost converter when the C36 capacitor is charged to 45V and then the MCU controls Open and close solenoid. The Boost regulator does not need to operate solenoid it only require to charge the capacitor to 45V.
The entire circuit is operating fine when only 2 capacitors (C33 & C35) are connected in 18V rail. For getting more backup time I have added an additional capacitor (C90) in the 18V (marked in the attached schematic) to preserve battery power so that micro controller in Low power mode can operate with capacitor power itself for at least 30 Sec. When the 3rd capacitor (C90) is added for some operation circuits works fine and after some time it stops working (the capacitor is getting charged only upto 20V). When I removed the 3rd Capacitor it works fine again.
I have checked the gate waveform of the Boost regulator with 2 capacitors and 3 capacitors. In both cases the mosfet operates in ~ 90% and drain waveform operates in ~10%. Wave form attached as Jpeg.
Fig 1: Channel 3: Mosfet Drain Waveform Channel 4: Mosfet Gate Waveform.
Fig 2: Channel 2: Mosfet Gate Waveform.
As per my understanding the dutycycle should be less than 75%. Maybe in 2 cases the boost regulator in operating not correctly due to miscalculated component values. Please help me to validate the Boost and buck circuit component selection and Please help me to solve this issue..
Also attaching 105V Boost circuit used to Open the solenoid. Please review the circuit components too.