LM3674MFX-1.8

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The LM3674MFX-1.8 is a voltage regulator specifically designed for power management applications, where features like ultra-low-power dissipation when regulating, an adjustable switching frequency, fixed voltage or pulse-width modulation (PWM) control modes, and maximum current startup at 0.25μA are featured. This voltage regulator belongs to the large class of DC-DC switching regulators, and it primarily designed for example for regulation of Point-of-Load (POL) outputs, shown in Figure 1. It has various advantageous features like small formfactor and advanced power management capability, making it a prime choice for applications such as laptops, personal digital assistants and other consumer and industrial electronics.

Figure 1. LM3674MFX-1.8 Application Field

The LM3674MFX-1.8 is a regulated output synchronous buck converter with a peak current-mode PWM topology, included low RDS(on) FETs and a low VIN(max) logic level shift gate drive. It supports power systems from 1.9V to 13V and can drive up to 3A output current into capacitive and dynamic loads. The device features cycle-by-cycle current limiting and thermal shutdown for maximum protection.

The low quiescent current of <25μA extends battery life and system efficiency in light-load environments. The operating frequency of LM3674MFX-1.8 is adjustable from 250kHz to 2.5MHz, allowing the use of small size inductor and output capacitors as well as reduces system noise emissions and minimizing external component count. Both the Fixed Voltage (FV) and Pulse-Width Modulation (PWM) mode are provided; the duty cycle can be adjusted to Change the Output voltage on the fly.

The LM3674MFX-1.8 has internal lower side FETs with low RDS(on) and incorporates a low voltage level shift gates drivers, allowing the use of simple N-Channel MOSFETs for the upper switch. This results in higher efficiency and reduced design complexity. The device also includes a number of other features like a Disable Mode, an Input Voltage Shutdown and Open Load Detection. The high switching frequency and low EMI of the device add to its great performance.

Working Principle

The typical operating system diagram of the LM3674MFX-1.8 is shown in Figure 2. The device is based on a synchronous buck topology that consists of two power transistors – high-side and low-side, built in internal FETs. The actual voltage control is obtained by varying the duty cycle of the Gate Driver outputs to the high and low side FETs. The peaks of those signals determine whether the FETs are on or off during each switching cycle.

Figure 2. Typical Operating System Diagram of LM3674MFX-1.8

The controller regulates the output voltage by sourcing and sinking current to the Load. When the voltage at the feedback pin is above the setpoint voltage, then the high-side FET is turned off, the low-side FET is turned on and current is sunk from the Load. When the voltage decreases below the setpoint voltage, then the high-side FET is turned on and the low-side FET is turned off and current is sourced to the Load. This closed-loop operation maintains the output voltage at the setpoint.

The LM3674MFX-1.8 is operative in either Fixed Voltage (FV) or Pulse-Width Modulation (PWM) Mode. In the FV mode, the current is limited by an internal “constant-current source” while the maximum duty-cycle and output current are limited. In the PWM mode, the output voltage regulation is obtained by varying the duty-cycle whereas the output current can be adjusted within the device’s specification.

The LM3674MFX-1.8 features an adjustable soft-start feature, which minimizes the inrush current during startup or when the output voltage is changed. The current limit is adjustable from 0A to 2A and the device provides over-temperature protection. For better overall thermal performance, a BAL(Bias Adjusted Logic) pin can be used as a reference voltage source, allowing the device to operation with minimal junction temperature changes.

In summary, the LM3674MFX-1.8 is a compact and innovative voltage regulator specifically designed for power management applications, featuring ultra-low-power dissipation, adjustable switching frequency, fixed voltage and PWM control modes and maximum current startup of 0.25μA. Its small form-factor, advanced power management capability, operating frequency range of 250kHz to 2.5MHz and low quiescent current of 25 μA make the LM3674MFX-1.8 a prime choice for applications such as laptops, personal digital assistants and other consumer and industrial electronics.

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