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

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