General Description
The AAT1171 SwitchReg™ dynamically controls the operating voltage of a WCDMA or CDMA power amplifier inside single-cell, lithium-ion battery-powered systems. The AAT1171 outputs a voltage between 0.6V and 3.6V, thereby optimizing the amplifier efficiency at both low and high transmit levels.
The AAT1171 output voltage is controlled via an analog signal from the baseband processor. It can deliver 600mA of continuous load current while maintaining a low 45μA of no load quiescent current. The 2MHz switch ing frequency minimizes the size of external components while keeping switching losses low. To further improve system efficiency, an 85mΩ bypass MOSFET transistor is also included to allow the PA to be powered directly from the battery.
The AAT1171 maintains high efficiency thoughout the entire load range in Light Load (LL) mode, and can be forced into Pulse Wide Modulation (PWM) mode for low noise operation or can be synchronized to an external clock.
The AAT1171 is available in a Pb-free, space-saving TDFN33-12 or 12-pin wafer-level chip scale package (WLCSP) and is rated over the -40°C to +85°C temperature range.

Features
• VIN Range: 2.7V to 5.5V
• Variable Output Voltage: 0.6V to 3.6V
• 600mA Output Current
• DAC Input: 0.2V to 1.2V
• High Output Accuracy: ±3%
• 45μA No Load Quiescent Current
• Internal Soft Start Limits Startup Current and Output
   Voltage Overshoot
• Synchronizable to External 19.8MHz System Clock
• Over-Temperature and Current Limit Protection
• Integrated 85mΩ Bypass MOSFET
• 2MHz Operation
• PWM/LL Control with Override
• Fast Start-Up:
▪ 50μs (AAT1171-4, AAT1171-5)
▪ 150μs (AAT1171-1)
• 100% Duty Cycle Operation
• <30μs Output Voltage Response Time
• 3x3mm 12-Pin TDFN or 1.535x2.235mm 12-Pin
   WLCSP Package
• Temperature Range: -40°C to +85°C

Applications
• WCDMA or CDMA PA in Cellular Phones, Smartphones,
   Feature Phones, etc.
• Express Card
• PCMCIA Data Cards