LM3243

• Input Voltage Range: 2.7 V to 5.5 V
• High-Efficiency PFM and PWM Modes With
  Internal Synchronous Rectification
• Analog Bypass Function with Low Dropout
  Resistance (45 mΩ Typical)
• Dynamically Adjustable Output Voltage: 0.4 V to
  3.6 V (Typical) in PFM and PWM Modes
• Maximum Load Current: 2.5 A in PWM Mode
• PWM Switching Frequency: 2.7 MHz (Average)
• Modulated Switching Frequency to Aid Rx Band
  Compliance
• Operates From a Single Li-ion Cell
  (2.7 V to 5.5 V)
• Current and Thermal Overload Protection
• ACB Reduces Inductor Requirements and Size
• Minimum Total Solution Size by Using Small
  Footprint and Case Size Inductor and Capacitors

The LM3243 is a DC-DC converter optimized for powering multi-mode 2G, 3G, and 4G RF power amplifiers (PAs) from a single Lithium-Ion cell. The LM3243 steps down an input voltage from 2.7 V to 5.5 V to a dynamically adjustable output voltage of 0.4 V to 3.6 V. The output voltage is set through a VCON analog input that adjusts the output voltage to ensure efficient operation at all power levels of the RF PA.

The LM3243 operates in constant frequency PWM mode producing a small and predictable amount of output voltage ripple. This enables best ECTEL power requirements in GMSK and EDGE spectral compliance, with the minimal amount of filtering and excess headroom. When operating in PFM mode, the LM3243 enables the lowest DG09 current consumption and therefore maximizes system efficiency.

The LM3243 has a unique ctive urrent assist and analog ypass (ACB) feature to minimize inductor size without any loss of output regulation for the entire battery voltage and RF output power range, until dropout. ACB provides a parallel current path, when needed, to limit the maximum inductor current to 1.4 A (typical) while still driving a 2.5-A load. The ACB also enables operation with minimal dropout voltage. When considering using the LM3243 in a system design, see the Layout section of this data sheet.