LM2623

SNVS188G – MAY 2004 – REVISED DECEMBER 2005

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DETAILED DESCRIPTION

OPERATING PRINCIPLE

The LM2623 is designed to provide step-up DC-DC voltage regulation in battery-powered and low-input voltage

systems. It combines a step-up switching regulator, N-channel power MOSFET, built-in current limit, thermal

limit, and voltage reference in a single 8-pin VSSOP package Figure 9. The switching DC-DC regulator boosts an

input voltage between .8V and 14V to a regulated output voltage between 1.24V and 14V. The LM2623 starts

from a low 1.1V input and remains operational down to below .8V.

This device is optimized for use in cellular phones and other applications requiring a small size, low profile, as

well as low quiescent current for maximum battery life during stand-by and shutdown. A high-efficiency gated-

oscillator topology offers an output of up to 2A at low output voltages.

Additional features include a built-in peak switch current limit, and thermal protection circuitry.

Figure 9. Functional Diagram

GATED OSCILLATOR CONTROL SCHEME

The on/off regulation mode of the LM2623, along with its ultra-low quiescent current, results in good efficiency

over a very wide load range. The internal oscillator frequency can be programmed using an external resistor to

be constant or vary with the battery voltage. Adding a capacitor to program the frequency allows the designer to

adjust the duty cycle and optimize it for the application. Adding a resistor in addition to the capacitor allows the

duty cycle to dynamically compensate for changes to the input/output voltage ratio. We call this a Ratio Adaptive

Gated Oscillator circuit. See the Application Notes for sample application circuits. Using the correct RC

components to adjust the oscillator allows the part to run with low ripple and high efficiency over a wide range of

loads and input/output voltages.

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