eorex

EP3001

Jul. 2006

www.eorex.com

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Idle Mode Operation

At very light loads, the EP3001 automatically enters Idle Mode. In the Idle Mode, the inductor current

may reach zero or reverse on each pulse. The PWM control loop will automatically skip pulses to

and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the

switching regulator.

Dropout Operation

When the input voltage decreases toward the value of the output voltage, the EP3001 allows the main

switch to remain on for more than one switching cycle and increases the duty cycle

reaches 100%. The output voltage then is the input voltage minus the voltage drop across the main

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 5:

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

IN

OUT

V

V

× 100%

Maximum Load Current

The EP3001 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.

Short-Circuit Protection

A current limit (1A) circuit is equipped in the EP3001, to protect the EP3001 when the output pin is

shorted to GND pin. This current limit will suppress the output current so that the inductor current has

enough time to decay.