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The AP3591 is a synchronous adaptive on-time buck controller providing high efficiency, excellent transient response and high DC output accuracy for low voltage regulation in notebook application.
The constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and features small external component count and fast transient response.
The operation mode is selectable by EN voltage. A Diode Emulation Mode (DEM) is activated for increasing efficiency at light loads, while PWM mode is activated only for low noise operation. The AP3591 also integrates internal Soft-start, UVLO, OVP, OTP, and programmable OCP to protect the circuit. A Power Good signal is employed to monitor the output voltage.
The AP3591 is available in U-QFN3535-14 package.


  • Notebook Computer, AIO PC
  • Low-voltage Distribute Power
  • I/O Supplies


  • Fixed Frequency Constant On-time Control; Resistor Programmable Frequency Adjustable from 100kHz to 700kHz
  • Good Stability Independent of the Output Capacitor ESR
  • Quick Load Step Response
  • Input Voltage Range: 4.5V to 26V
  • Output Voltage Range: 0.75V to 5.5V
  • CCM/DEM Mode Selection
  • Integrated Bootstrap Diode
  • Resistor Programmable Current Limit by Low-side RDSON Sense
  • Integrated Negative Over Current Limit
  • Integrated OVP/UVP and Over Thermal Shutdown Function
  • Power Good Indicator
  • Internal Soft-start
  • Integrate Output Discharge (Soft-stop)
  • Safe Start-up into Pre-biased Loads
  • Totally Lead-Free & Fully RoHS Compliant 
  • Halogen and Antimony Free. “Green” Device

Product Specifications

Product Parameters

Type Buck
Minimum Input Voltage 4.5 V
Maximum Input Voltage 26 V
Output Voltage 0.75 to 5.5 V
Frequency 100K to 700K Hz
Efficiency 93 %

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