LT1577CS-ADJ/ADJ#TRPBF

Overview

The LT1577CS-ADJ/ADJ#TRPBF is a dual controller IC for ultrafast transient response, low dropout regulators. It drives external N-channel MOSFETs as source followers to eliminate bulk output capacitors in demanding microprocessor applications. The device features a precision-trimmed adjustable reference voltage with ±1% tolerance over temperature and typical load regulation of 1mV. It incorporates high-side sense current limiting with a fault protection timer circuit and a multifunction shutdown pin providing latchoff, overvoltage, or thermal protection.

Feature Summary

• UltraFast transient response eliminates the need for expensive tantalum or electrolytic output capacitors
• Dual controller architecture driving external N-channel MOSFETs as source followers
• High-side sense current limit amplifier activates a fault protection timer circuit
• Multifunction shutdown pin provides latchoff, overvoltage protection, or thermal shutdown

Applications

• Pentium processor supplies
• PowerPC supplies
• Microprocessor supplies stepping down from 5V to 3.3V or 3.3V to lower voltages
• GTL termination
• Low voltage logic supplies

Procurement Notes

Verify that the specific ordering suffix matches the required package and tape/reel configuration. Confirm the component meets the intended operating temperature range and electrical specifications for your application. Ensure compatibility with external N-channel MOSFET selection regarding gate drive requirements and RDS(ON) characteristics.

Selection Notes

Select this component when designing power supplies for modern microprocessors requiring extremely fast load transient response without bulk output capacitance. The dual channel design allows for generating two independent regulated outputs from a single package. Consider the external N-channel MOSFET selection carefully, as the dropout voltage is defined by the MOSFET's RDS(ON).

Part Context

This part belongs to the LT1575/LT1577 family of ultrafast transient response, low dropout regulator controllers. While the LT1575 is a single controller, the LT1577 integrates two identical regulator channels into a single 16-lead narrow body SO package. Both families share the same core architecture for driving external MOSFETs to achieve superior bandwidth and transient performance compared to traditional linear or switching regulators.

Replacement Considerations

LT1577CS-3.3/ADJ

FAQ

How does the LT1577 achieve ultrafast transient response?

It achieves this by eliminating expensive tantalum or bulk electrolytic output capacitors. The controller drives external N-channel MOSFETs as source followers, allowing the regulator to respond to load changes in a few hundred nanoseconds.

What is the function of the SHDN pin?

The SHDN pin is a multifunction shutdown pin that provides GATE drive latchoff capability. It can be used for current limit time-out with latchoff, overvoltage protection, or thermal shutdown depending on the external components connected to it.

How is current limiting implemented in the LT1577?

Current limiting is implemented using a high-side sense current limit amplifier. A small sense resistor is connected in series with the drain of the external MOSFET between the IPOS and INEG pins. When the voltage across this resistor reaches the threshold, the amplifier activates the fault protection timer.