Features
High efficiency switcher core with integrated low RDSon power MOSFETs
Resistor programmable switching frequency with frequency synchronization
Internal soft-start with monotonic and pre-biased startup
Low shutdown quiescent current
Precision enable with hysteresis
PGOOD indicator function
Input under-voltage lock-out (UVLO)
Output over-voltage protection (OVP)
High-bandwidth load transient response with peak current-mode control
Cycle-by-cycle current limiting
Thermal shutdown
Description The LM21305 is a full-featured 5A synchronous buck POL regulator optimized for solution size, flexibilty, and high conversion
efficiency. High power density LM21305 designs are achieved via monolithic integration of the high-side and low-side power
MOSFETs, high switching frequency, current-mode control, and optimized thermal design. The efficiency of the LM21305 is elevated
at light loads with diode emulation mode operation and at heavy loads by optimal design of the MOSFET gate drivers to minimize
switch dead-times and body-diode conduction losses.
The LM21305 accepts a wide input voltage range of 3V to 18V, facilitating interface to all intermediate bus voltages, including
3.3V, 5V and 12V rails. An output voltage as low as 0.598V is supported with excellent setpoint accuracy and low ripple and
RMS noise. The LM21305 offers flexible system configuration with programmable switching frequency from 300 kHz to 1.5 MHz
using one resistor or via external clock synchronization. On-chip bias supply sub-regulators alleviate the need for external
bias power and simplify PCB layout. The device also offers internal soft-start to limit inrush current, pre-biased and monotonic
startup capability, 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 and enables excellent line and
load transient response.
Offered in a thermally enhanced LLP-28 package, the LM21305 features internal output over-voltage and over-current protection
circuits for increased system reliability. A precision enable pin and integrated input UVLO allow the turn-on of the device
to be tightly controlled and sequenced. An integrated open-drain power good indicator provides power rail sequencing capability
and fault indication.
Key Specification
Single-rail input voltage range from 3V to 18V
0.598V feedback voltage reference
300 kHz to 1.5 MHz switching frequency range
LLP-28 package (5 x 5 x 0.8 mm, 0.5 mm pitch)
Applications
POL regulation from 3.3V, 5V, and 12V supply rails
High efficiency supply for DSPs, FPGAs, ASICs and processors
Broadband, networking and optical communications infrastructure
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Typ app circuit
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LM20343
