“The project described here is a high voltage step-down regulator based on A4447 general-purpose buck converter chip from Allegro Semiconductor. The output voltage of the board is configured at 3.3V, but it is adjustable from 0.8 to 24V, based on the resistor divider R2 and R5. Connector CN1 is for DC input 24V-42V, Connector CN2 is DC Output. Refer to the information below to adjust various voltage outputs.
Divider Resistor Value for 1.5V, 1.8V, 3.3V, 5V Output
- 1.5V: R2=1.3K, R5=1.47K Ohms
- 1.8V: R2=2.55K, R5=2K Ohms
- 3.3V: R2= 3K, R5=910 Ohms
- 5V: R2=6.34K, R5=1.2K Ohms
The chip has a soft start feature, which allows the output to slowly ramp upon startup. This limits the maximum demand on the external power supply by controlling the inrush current required to charge the external capacitor and any DC load at start-up. Internally, the ramp is set to 10 ms nominal rise time. During soft-start, the current limit is 2.2A minimum. ENB pin is connected to the ground to enable the device and begin the soft-start sequence.”