The LM21305 is a full-featured, 5-A, synchronous buck dc-dc converter optimized for solution size, flexibility, and high conversion efficiency. High-power density LM21305 designs are easily achieved by virtue of monolithic integration of high-side and low-side power MOSFETs, high switching frequency, peak current-mode control, and optimized thermal design. The efficiency of the LM21305 is maximized at light loads with diode emulation mode operation and at heavy loads by optimal design of the MOSFET adaptive gate drivers to minimize switch dead-times and body-diode conduction losses.

The LM21305 accepts a wide input voltage range of 3 V to 18 V for interface to various intermediate bus voltages, including 3.3-V, 5-V, and 12-V rails. A 1.5% voltage reference and 70-ns, high-side MOSFET minimum controllable on-time enable output voltages as low as 0.598 V with excellent setpoint accuracy. The LM21305 is available in a 5-mm × 5-mm² WQFN-28 thermally-enhanced package with 0.5-mm pitch.

The LM21305 offers flexible system configuration with programmable switching frequency from 300 kHz to 1.5 MHz using one resistor or by external clock synchronization for beat-frequency-sensitive and multi-regulator applications. On-chip bias supply low-dropout (LDO) sub-regulators eliminate the need for an external bias power and simplify circuit board layout. The device also offers an internal soft-start to limit inrush current and provide monotonic startup capability into unbiased and pre-biased loads, integrated boot diodes, cycle-by-cycle current limiting, and thermal shutdown. Peak current-mode control with a high-gain error amplifier maintains stability throughout the entire input voltage and load current ranges, enabling excellent line and load transient response.

The LM21305 features internal output overvoltage protection (OVP) and overcurrent protection (OCP) circuits for increased system reliability. An integrated open-drain, PGOOD indicator provides output voltage monitoring, power-rail sequencing capability, and fault indication. Other features include thermal shutdown with automatic recovery, low PWM minimum on-time, low shutdown quiescent current, and precision enable with hysteresis for programmable line undervoltage lockout (UVLO).

• High-Efficiency Synchronous DC-DC Converter:
  • Integrated Low RDSon Power MOSFETs
  • Wide Input Voltage Range: 3 V to 18 V
  • Load Current as High as 5 A
  • Switching Frequency: 300 kHz to 1.5 MHz
• External Frequency Synchronization
• Accurate 0.598-V Feedback Voltage Reference
• Ultra-Fast Line and Load Transient Response:
  • Peak Current-Mode Control
  • Internal Slope Compensation
  • High-Bandwidth Error Amplifier
• Ultra-Low Shutdown Quiescent Current
• Wide Duty-Cycle Operating Range:
  • TON-MIN: 70 ns for Low VOUT
  • TOFF-MIN: 50 ns for High Duty Cycle
• Diode Emulation Mode at Light Loads
• Integrated Bias Supply LDO Sub-Regulators
• Internal Soft-Start Function:
  • Monotonic Startup into Pre-Biased Loads
• Precision Enable Input with Hysteresis
• Open-Drain PGOOD Indicator
• Internal Input Undervoltage Lockout (UVLO)
• Cycle-by-Cycle Overcurrent Protection
• Output Overvoltage Protection (OVP)
• Thermal Shutdown Protection with Hysteresis
• 5-mm × 5-mm WQFN-28 PowerPAD? Package

• Vin (Min) (V)
• 3
• Vin (Max) (V)
• 18
• Vout (Min) (V)
• 0.6
• Vout (Max) (V)
• 0.6
• Iout (Max) (A)
• 5
• Iq (Typ) (uA)
• 9000
• Switching frequency (Min) (kHz)
• 300
• Switching frequency (Max) (kHz)
• 1500
• Features
• Enable, Frequency Synchronization, Power Good, Pre-Bias Start-Up, Synchronous Rectification
• Rating
• Catalog
• Regulated outputs (#)
• 1
• Control mode
• Current Mode
• Duty cycle (Max) (%)
• 100

LM21305的完整型号有：LM21305SQ/NOPB、LM21305SQE/NOPB、LM21305SQX/NOPB，以下是这些产品的关键参数及官网采购报价：

LM21305SQ/NOPB，工作温度：-40 to 85，封装：WQFN (RSG)-28，包装数量MPQ：1000个，MSL 等级/回流焊峰值温度：Level-2A-260C-4 WEEK，引脚镀层/焊球材料：SN，TI官网LM21305SQ/NOPB的批量USD价格：2.904（1000+）

LM21305SQE/NOPB，工作温度：-40 to 85，封装：WQFN (RSG)-28，包装数量MPQ：250个，MSL 等级/回流焊峰值温度：Level-2A-260C-4 WEEK，引脚镀层/焊球材料：SN，TI官网LM21305SQE/NOPB的批量USD价格：2.904（1000+）

LM21305SQX/NOPB，工作温度：-40 to 85，封装：WQFN (RSG)-28，包装数量MPQ：4500个，MSL 等级/回流焊峰值温度：Level-2A-260C-4 WEEK，引脚镀层/焊球材料：SN，TI官网LM21305SQX/NOPB的批量USD价格：2.42（1000+）

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