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MAX639, MAX640, MAX653

5V/3.3V/3V Adjustable, High-Efficiency, Low-IQ, Step-Down DC-DC Converters

Low Supply Current, High-Efficiency Over Wide Load Range
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The MAX639/MAX640/MAX653 step-down switching regulators provide high efficiency over a wide range of load currents, delivering up to 225mA. A current-limiting pulse-frequency-modulated (PFM) control scheme gives the devices the benefits of pulse-width-modulated (PWM) converters (high efficiency at heavy loads), while using only 10µA of supply current (vs. 2mA to 10mA for PWM converters). The result is high efficiency over a wide range of loads.

The MAX639/MAX640/MAX653 input range is 4V to 11.5V, and the devices provide lower preset output voltages of 5V, 3.3V, and 3V, respectively. Or, the output can be user-adjusted to any voltage from 1.3V to the input voltage.

The MAX639/MAX640/MAX653 have an internal 1A power MOSFET switch, making them ideal for minimum-component, low- and medium-power applications. For increased output drive capability, use the MAX649/MAX651/MAX652 step-down controllers, which drive an external P-channel FET to deliver up to 5W.

Data Sheet

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Key Features

  • High Efficiency for a Wide Range of Load Currents
  • 10µA Quiescent Current
  • Output Currents Up to 225mA
  • Preset or Adjustable Output Voltage:
    • 5.0V (MAX639)
    • 3.3V (MAX640)
    • 3.0V (MAX653)
  • Low-Battery Detection Comparator
  • Current-Limiting PFM Control Scheme


  • 5V to 3.3V Conversion
  • 9V Battery to 5V, 3.3V, or 3V Conversion
  • High-Efficiency Linear Regulator Replacement
  • Portable Instruments and Handy-Terminals

Key Specifications:

Step-Down Switching Regulators
Part Number VIN
Preset VOUT
Output Adjust. Method IOUT1 (max)
Switch Type Power Good Signal DC-DC Outputs Budgetary
min max min max See Notes
MAX639  4 11.5 1.3 11.5
0.225 Internal Yes 1 $3.38 @1k
MAX640  3.3 $3.38 @1k
MAX653  3 $1.55 @1k
See All Step-Down Switching Regulators (310)

Pricing Notes:

This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.


MAX639, MAX640, MAX653: Typical Operating Circuit
Typical Operating Circuit

Notes and Comments

Ultra-low IQ

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Document Ref.: 19-4505 Rev 4; 2005-09-07
This page last modified: 2007-07-17