5V Adjustable Step Down DC-DC Converter: MAX639 Maximize

5V Adjustable Step Down DC-DC Converter: MAX639

Step down a high voltage such as one from a 9V battery to 5V using this MAX639 Step Down DC-DC Converter. You can also adjust the output voltage from 1.3V to the input voltage via the VFB pin!

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This adjustable Step Down DC-DC converter performs the functions of a standard 5V regulator and more! In addition to pulling down a 4V - 11.5V input to 5V output by default, you can also adjust the output voltage by connecting a voltage divider to the VFB (feedback) pin. 


  • Output Voltage:
    • 5V by default
    • adjustable from 1.3V to Vin (by connecting a voltage divider circuit to VFB pin)
  • Input Voltage: 4V - 11.5V
  • Can be used as a standard 5V regulator or as an adjustable regulator!
  • High Efficiency
  • Low Iq
  • Designing power supplies with the MAX639 is easy. The few required external components are readily available. The most general applications use the following components:
    1. Capacitors: For the input and output filter capacitors, try using electrolytics in the 100μF range, or use low-ESR capacitors to minimize output ripple. Capacitor values are not critical.
    2. Diode: Use the popular 1N5817 or equivalent Schottky diode.
    3. Inductor: For the highest output current, choose a 100μH inductor with an incremental saturation current rating of at least 600mA. To obtain the highest efficiencies and smallest size, refer to the Inductor Selection section on the datasheet.