LM3677LEX-1.8/NOPB

Voltage - Output (Min/Fixed):	1.8V
Base Part Number:	LM3677
Supplier Device Package:	6-LLP (2.0x1.5)
Package / Case:	6-UFDFN
Mounting Type:	Surface Mount
Operating Temperature:	-30°C ~ 85°C (TA)
Synchronous Rectifier:	Yes
Frequency - Switching:	3MHz
Current - Output:	600mA
Voltage - Output (Max):	--
Series:	--
Voltage - Input (Max):	5.5V
Voltage - Input (Min):	2.7V
Number of Outputs:	1
Output Type:	Fixed
Topology:	Buck
Output Configuration:	Positive
Function:	Step-Down
Part Status:	Obsolete
Packaging:	Tape & Reel (TR)

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The LM3677LEX-1.8/NOPB is a highly integrated and High-Efficiency DC-DC Buck Regulator from TI Texas Instruments. It is a SMBus interface-based, highly efficient, high-performance, high-accuracy, step-down switching regulator designed for use in applications such as memory power supplies and digital microprocessors. It is part of the LM3677LEX family of devices that include both a step-down and step-up regulator. It comes in a small 5-lead Pb-free T&R package, is available in both a 1.8V and 2.5V version and is designed to deliver up to 2A of current.

The LM3677LEX-1.8/NOPB features an integrated low-dropout (LDO) linear regulator, an adjustable input voltage range from 3.15 V to 6.0 V and an adjustable switching frequency from 300 kHz to 2 MHz. It includes an integrated low-dropout (LDO) linear regulator that provides up to 1A for supply voltages between 0.8 V and 3.3 V, and an integrated, adjustable step-up (BulkVolt)regulator that provides up to 2 A for supply voltages between 0.8 V and 3.6 V. The LM3677LEX-1.8/NOPB also features integrated loop compensation, an adjustable 1.5A peak-current-mode step-down switch and an adjustable soft-start circuit.

1. Application Field

The LM3677LEX-1.8/NOPB is best suited for DC-DC converter systems that require a high degree of integration, high efficiency, accurate tracking, and robustness. It enables a highly integrated design with a minimum of external components, providing protection against over-voltage, over-current, over-temperature and under-voltage conditions. It supports SMBus, I2C and PMBus communications, allowing for the monitoring and control of the power supply system. Typical applications for the LM3677LEX-1.8/NOPB include memory power supplies, microprocessors, DSPs, low power audio systems, servers and storage systems, handheld devices, 1U/2U modular system and various portable applications.

2. Working Principle

The LM 3677LEX-1.8/NOPB is a synchronous step-down voltage regulator that uses a fixed frequency peak current-mode control architecture. It achieves high efficiency by operating in Burst ModeTM, which is a combination of skip cycle and pulse-width modulation (PWM) modes. The adjustment of the output voltage is achieved by adjusting the duty cycle of the power switch. The power switch is turned on by the rising edge of the current mode signal and is turned off by the falling edge of the soft-start signal. The current mode signal is generated by comparing the average inductor current to a reference voltage. The voltage across the output capacitor is compared to the reference voltage, and the error signal is used to adjust the current mode signal amplitude. The current mode signal is summed with the output voltage signal and compared to an internal reference voltage to generate the soft-start signal.

The LM3677LEX-1.8/NOPB also includes an integrated low-dropout (LDO) linear regulator and an adjustable low-side switch enabled by the PMBus Interface. The LDO is controlled by a voltage feedback loop, which maintains a constant output voltage regardless of changes in the input voltage. The voltage regulator loop is closed by a digital-to-analog converter (DAC) connected to the PMBus Interface. The LM3677LEX-1.8/NOPB also offers adjustable current limit and over-temperature protection.

The LM3677LEX-1.8/NOPB is designed to meet the most stringent requirements of the latest standards, such as the Electrical Overstress (EOS) and Electrostatic Discharge (ESD) specifications. It has been designed to drive any bus with a minimum of 5V to the output, allowing for the most efficient delivery of power to its intended load. Its high-side switch and high efficiency make it suitable for applications where a high amount of power is required.

In conclusion, the LM3677LEX-1.8/NOPB is a part of TI’s family of devices that combines a step-down and step-up regulator in a single package, providing an integrated high-efficiency DC-DC buck regulator. It is designed to provide high accuracy, robustness, and up to 2A of current with a flexible input voltage range and adjustable switching frequency. Its low-dropout linear regulator and adjustable low-side switch allow for the monitoring and control of the power supply system, making it suitable for a range of industries, including memory power supplies, microprocessors, DSPs, low power audio systems, servers and storage systems, handheld devices, 1U/2U modular systems, and other portable applications.

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