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