General Description
AP1539 consists of step-down switching regulator with PWM control. These devices include a reference voltage source, oscillation circuit, error amplifier, internal PMOS. AP1539 provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to vary the duty ratio linearly from 0 up to 99%. This converter also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. An enable function, an over current protect function and a short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced from 300KHz to 50KHz.

FEATUREs
• Input voltage: 3.6V to 18V
• Output voltage: 0.8V to VCC
• Output current: up to 4A
• Duty ratio: 0% to 99% PWM control
• Oscillation frequency: 300KHz typ.
• Soft-start like, Current limit and Enable function
•Thermal Shutdown function
• Built-in internal SW P-channel MOS
• SOP-8L-DEP: Available in “Green” Molding Compound(No Br, Sb) 
• Lead Free Finish / RoHS Compliant