EP3003 Datasheet, PDF (8/12 Pages) Eorex Corporation – 2-CH, 600mA Synchronous Step-down Converter

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
across the main switch and the inductor. At low input supply voltage, the R_DS(ON) of the P Channel
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:
D = T_ON x f_OSC x 100% ≈ V_OUT/V_IN x 100%
where T_ON is the main switch on time, and f_OSC is the oscillator frequency (1.5MHz).
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:
V _out
= 0 .6V _⎜⎛1 +
⎝
R 2 _⎟⎞
R1 _⎠
R1 = 150KΩ; R2 = 300KΩ for V_OUT = 1.8V;
R3 = 100KΩ; R4 = 330KΩ for V_OUT = 2.5V.
Rev.01
8