GENERAL DESCRIPTION
The ADP1621 is a fixed-frequency, pulse-width modulation (PWM), current-mode, step-up converter controller. It drives an external n-channel MOSFET to convert the input voltage to a higher output voltage. The ADP1621 can also be used to drive flyback, SEPIC, and forward converter topologies, either isolated or nonisolated.
The ADP1621 eliminates the use of a current-sense power resistor by measuring the voltage drop across the on resistance of the n-channel MOSFET. This technique, allowed up to a maximum voltage of 30 V at the switch node, maximizes efficiency and reduces cost. For switch-node voltages higher than 30 V or for more accurate current limiting, the CS pin can be connected to a current-sense resistor in the source of the MOSFET.

FEATURES
   92% efficiency (no sense resistor required)
   ±1.0% initial accuracy
   IC supply voltage range: 2.9 V to 5.5 V
   Power-input voltage as low as 1.0 V
   Capable of high supply input voltage (>5.5 V)
      with an external NPN or a resistor
   VIN UVLO and 35 mA shunt regulator
   External slope compensation with 1 resistor
   Programmable operating frequency
      (100 kHz to 1.5 MHz) with 1 resistor
   Lossless current sensing for switch-node voltage <30 V
   Resistor current sensing for switch-node voltage >30 V
   Synchronizable to external clock
   Current-mode operation for excellent line and load transient
      responses
   10 μA shutdown current
   Current limit and thermal overload protection
   Soft start in 2048 clock cycles
   Supported by ADIsimPower™ design tool

APPLICATIONS
   APD bias
   Portable electronic equipment
   Isolated dc-to-dc converter
   Step-up/step-down dc-to-dc converter
   LED driver for laptop computer and navigation system
   LCD backlighting