The input power comes from an external 10-24V supply and enters the system at J1. The input voltage is regulated down to 3.3V, 5V and V_LCD which can be configured as a 5V or 3.3V output via a shunt. Likewise, the input voltage is regulated up or down to provide 12V for the LCD display. Each supply has an LED associated with it that illuminates when the supply is on. Refer to Section 0.
Low Power Regulation
To generate the 5V, a Texas Instrument TPS54140 Buck switch with adjustable output is used. The TPS54140 can supply up to 1.5A of current and provides over current protection. The TPS54140 is configured to regulate at 5V via the VSENSE voltage which is set by R6 and R9. R5 and R57 also provide an under voltage protection and will only allow the supply to regulate if the input voltage is greater than 9.18V.
PWR_OK is routed to the Com Express module indicating all power supplies are valid.
To generate the 3.3V, a Texas Instrument TPS54140 Buck switch with adjustable output is used. The TPS54140 can supply up to 1.5A of current and provides over current protection.
The TPS54140 is configured to regulate at 3.3V via the VSENSE voltage which is set by R14 and R59. R10 and R58 also provide an under voltage protection and will only allow the supply to regulate if the input voltage is greater than 9.18V.
The PWRGD signal, being an open-drain output is connected to PWR_OK signal of the 5V regulator.
The V_LCD rail for the LVDS monitor is also derived using a Texas Instrument TPS54140 Buck switch with adjustable output. The TPS54140 can supply up to 1.5A of current and provides over current protection. The TPS54140 is configured to regulate at 3.3V or 5V via the VSENSE voltage which is set by R64, R65 and R56. The Shunt J11 adds R64 to the circuit and if not installed, adjusts the output to be 5V and if installed, creates a parallel resistance between R64 and R65 (31.6K) and adjusts the output to be 3.3V.
The Enable input is pulled up to 3.3V and if the shunt J10 is not installed, the regulator is enabled. If J10 is installed, then software can control the enable via the V_LCD_ON signal from the Com Express Module.