Detailed Description

OPERATING PRINCIPLE

The LM2623 is designed to provide step-up DC-DC voltage

regulation in battery-powered and low-input voltage sys-

tems. It combines a step-up switching regulator, N-channel

power MOSFET, built-in current limit, thermal limit, and volt-

age reference in a single 8-pin MSOP package Figure 1. 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.

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 addi-

tion 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.

20038814

FIGURE 1. Functional Diagram

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