Maxim > Design Support > Technical Documents > Reference Schematics > Power-Supply Circuits > APP 5815 Keywords: 4-20mA current loops, HVAC and building control, high-voltage LDO replacement, general-purpose point-of-load REFERENCE SCHEMATIC 5815 Palo Verde (MAXREFDES33 ): Step-Down Converter Feb 27, 2014 Abstract: The Palo Verde reference design (MAXREFDES33 ) is a high-efficiency, high-voltage, synchronous step-down DC- DC converter with integrated MOSFETs operating over a 4.5V to 60V input voltage range and delivering output current up to 300mA at 3.3V. Test results and hardware files provide complete documentation for designs. The board is also available for purchase. Introduction The Palo Verde (MAXREFDES33 ) subsystem reference design (Figure 1) demonstrates the application of the MAX15062A 60V, 300mA ultra- small, high-efficiency, synchronous step-down converter. The reference design operates over a wide 4.5V to 60V input voltage range, and provides up to 300mA at 3.3V output. The device features undervoltage lockout, overcurrent protection, and thermal shutdown. The MAX15062A switches at a fixed frequency of 500kHz, and delivers a peak efficiency of 86.77% with the supplied components when the input is 24V. This general-purpose power solution can be used in many different types of power applications, such as 420mA current loops, HVAC and building control, high-voltage LDO replacement, general-purpose point-of-load, etc. In this reference design, the MAX15062 performs in 24V input applications, such as industrial sensors, process control, etc. Page 1 of 6System Diagram Figure 1. Typical industrial control power system diagram. Features Applications Minimal external components and low system cost Industrial sensors Versatile functionality allows stocking of fewer DC-DC regulators Process control Low power dissipation 420mA current loops Reliable operation in adverse industrial environments General-purpose point-of-load High-voltage LDO replacement Pmod -compatible form factor HVAC and building control PLCs Detailed Description of Hardware The Palo Verde subsystem reference design is a high-efficiency, high-voltage, synchronous step-down DC-DC converter solution with integrated MOSFETs. Palo Verde operates over a wide 4.5V to 60V input voltage range. The converter delivers output current up to 300mA at 3.3V. When EN/UVLO and VCC UVLO are satisfied, an internal power-up sequence soft-starts the error-amplifier reference, resulting in a clean monotonic output-voltage soft-start independent of the load current. The VOUT pin monitors the output voltage through an internal resistor-divider. RESET transitions to a high-impedance state 2ms after the output voltage reaches 95% of regulation. The device selects either PFM or forced-PWM mode depending on the state of the MODE pin at power-up (this reference design sets the device in PWM mode). By pulling the EN/UVLO pin to low, the device enters the shutdown mode and consumes only 2.2A (typical) of standby current. The reference design switches at a fixed frequency of 500kHz, and delivers a peak efficiency of 86.77% with the supplied components when the input is 24V. This reference board is designed in a Pmod-compatible form factor with IO pass-through, but can be used in any 4.5V60V to 3.3V power application up to 300mA. Page 2 of 6