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LM1770 #2: 3.3V @ 4A, 5V in, (Page 3)

Summary

The controller utilizes a constant on-time control scheme which eliminates the need for external compensation components, allowing the power supply designer to minimize necessary board space and reduce costs.

This design operates at 500 kHz and utilizes larger valued components to enable a high maximum output current. A 2.2 µH inductor and a 150 µF POSCAP output capacitor are used to generate the necessary ripple at the output and a 1 nF feed-forward capacitor is used to help stabilize the design. Due to the large current being switched on the board, a larger 150 µF electrolytic input capacitor is used.

The SI9433BDY PFET and SI4894DY NFET provide the necessary power handling capabilities to switch the large output current in this design, and the 2000 ns LM1770 timing option operates at 500 kHz in this configuration.

Specifications

Manufacturer	Texas Instruments
Category	AC/DC and DC/DC Conversion
Sub-Category	DC/DC SMPS - Single Output
Eval Board	ABC
Topology	Step Down
Outputs and Type	1 Non-Isolated
Output Voltage: Factory Set	3.3 V
Current Out	4 A
Voltage In	5 V
Efficiency @ Conditions	>92%, 5 Vin, 3.3V @ 0.5 ~ 4 A
Voltage Out Range
Features	Short Circuit Protection Soft Start
Switching Frequency	500 kHz
Standby Current [Typical]
Quiescent Current [Typical]	400 µA
Component Count + Extras	9 + 0
Internal Switch	No
Design Author	Texas Instruments
Application / Target Market	Computers DVD Players Point of Load (PoL) Portable Devices Set-Top Boxes Telecom USB Powered Devices White Goods
Main I.C. Base Part	LM1770U
Standby Current [Maximum]
Quiescent Current [Maximum]	600 µA
Date Created By Author
Date Added To Library	2011-03