POWER AND LINEAR IC SOLUTIONS

Wide Input-Range Synchronous Step-Down DC/DC Controller

The LTC3851/-1 from Linear Technology Corporation is a highly efficient, wide input-voltage range, synchronous step-down switching regulator controller that drives all N-channel power MOSFET stages and has coincident or ratiometric output voltage tracking.



The 4V to 38V input range encompasses a wide variety of applications, including most intermediate bus voltages and battery chemistries.

The device includes strong onboard MOSFET gate drivers to allow the use of high-power external MOSFETs to produce output currents of up to 20A with output voltages ranging from 0.8V to 5.5V, making the LTC3851/-1 well suited for point-of-load regulator requirements. Applications include datacom, telecom, industrial, automotive and medical systems, multifunction printers, displays and set-top boxes.

Its constant-frequency current-mode architecture provides a selectable fixed or synchronisable frequency from 250kHz to 750kHz using a Phase-Locked-Loop (PLL). OPTI-LOOP® compensation allows the transient response to be optimised over a wide range of output capacitance and ESR values, including all ceramic capacitor designs.

Output current sensing is accomplished by measuring the voltage drop across the output inductor or by using an optional sense resistor. Current foldback limits MOSFET heat dissipation during short-circuit and over-load conditions.

In addition, the LTC3851/-1 has adjustable soft-start to control the turn-on time and manage inrush current. Selectable continuous, pulse skip or Burst Mode operation are user-controllable to allow the designer to choose the right combination of efficiency and output ripple at light loads.

The LTC3851/-1 features a precision 0.8V reference with an accuracy of ±1% over a -40°C to 85°C operating temperature range. With up to 99% duty cycle, the device has a very low drop-out voltage, a useful feature for extending run times in battery powered applications. The LTC3851-1 features a power-good signal instead of current-limit threshold programmability.

Available packages include a thermally enhanced 3mm x 3mm QFN-16, MSOP-16E and narrow SSOP-16.

Features

• Highly efficient synchronous step-down switching controller
• Wide input voltage range: 4V to 38V
• Coincident or ratiometric output voltage tracking
• V_out range 0.8V to 5.5V
• Constant-frequency current-mode operation
• Fixed or synchronisable frequency: 250kHz to 750kHz
• Programmable soft-start
• User-controlled continuous, pulse skip or Burst Mode operation
• On-chip 0.8V reference (±1% from -40°C to +85°C)
• Low drop-out voltage
• Power-good signal

Applications

• Datacom
• Telecom
• Industrial
• Automotive
• Multifunction printers
• Displays
• Set-top boxes

For further information, including the Linear Technology LTC3851 Datasheet, please click here