Rev.01

8

EP3003

Dropout Operation

The EP3003 allows the main switch to remain on for more than one switching cycle and increases the

duty cycle until it reaches 100%. The output voltage then is the input voltage minus the voltage drop

MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure

the heat dissipated not to exceed the maximum junction temperature of the IC.

Note 3. The duty cycle D of a step-down converter is defined as:

Maximum Load Current

The EP3003 will operate with input supply voltage as low as 2.5V, however, the maximum load current

decreases at lower input due to large IR drop on the main switch and synchronous rectifier. The slope

compensation signal reduces the peak inductor current as a function of the duty cycle to prevent

sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the

duty cycle decreases.

APPLICATIONS INFORMATION

A general application circuit for EP3003 is shown in Figure 1, which is the baseline for some calculation

mentioned below. All external component selection for EP3003 application design will be illustrated as

the following.

Setting the Output Voltage

The external resistor sets the output voltage according to the following equation:

⎟

⎠

⎞

⎜

⎝

⎛ +

=

1

2

1

6

.

0

R

R

V

V

out