Description
The SC251 is a synchronous step-down converter designed for use as an adaptive voltage supply for WCDMA RF power amplifiers (PAs). An analog control input is used to adjust the output voltage dynamically between 0.5V and 3.4V using a non-linear transfer function. The non-linear relationship maximizes total system efficiency by providing the PA with the minimum voltage it needs to maintain linearity. For output voltages greater than 3.4V the input is connected directly to the output via an internal PMOS switch.
Features
◆ VOUT exponentially proportional to VDAC for maximum efficiency (patent pending)
◆ Output range and pass-through mode - 0.5V to 3.4V
◆ Output current - 800mA
◆ Shutdown current - < 1μA
◆ LDO PA bias supply - 2.85V, 10mA
◆ Internal clock - 1MHz
◆ Continuous short circuit protection on VOUT
◆ Duty cycle mode - 100%
◆ Internal PMOS bypass transistor
◆ Gate drive available for external bypass transistor
◆ Over 90% efficiency
◆ Low and high power modes for optimum dual-mode PA efficiency
◆ Switching time (lowest to highest output) < 40μs
◆ Micro-lead frame package MLPD-10, 3mm x 3mm

Applications
◆ 3G mobile phones - RF PA power supply
◆ WCDMA power amplifier modules
◆ Wireless modems