L5971D

L5971D application field and working principle

The L5971D is a synchronous step-down DCDC switch mode current regulator from STMicroelectronics, part of the STSTEP family of integrated circuits for power management, designed for wide-input voltage, low-voltage and low-noise applications. It is a dc-dc buck controller which encompasses adaptive voltage scaling and integrated dual N-Channel MOSFETs, making it efficient and cost-effective for use in low-power applications.

The L5971D regulator is designed to operate from a wide input voltage of between 8 V and 28 V and provides an adjustable output voltage ranging between 1.3 V and 20 V, adjustable via a single external resistor. It incorporates several protection features such as input undervoltage lockout with hysteresis, overvoltage protection (OVP) and an adjustable output overcurrent protection (OCP) with linear current limit (LCL). The L5971D also includes output voltage accuracy, over temperature protection and an adjustable current mode architecture to ensure the regulator stays regulated within its specified parameters regardless of output voltage and current consumption.

Application fields:

• Low voltage and low-noise DC-DC Buck regulators
• Power Management
• Portable Electronics
• White Goods and Home/Industrial Appliances
• Hybrid Electric Vehicles
• Industrial Automation and Robotics
• Distributed Power Architectures

Work principle:

The synchronous step-down DCDC switch mode current regulator based on the L5971D circuit is a switching regulator, which works as follows:

When the input voltage is greater than the set switching threshold, the circuit turns on the N-channel MOSFET, which allows current to flow to the input capacitor; this stored energy is then used to charge the output capacitor. The output voltage is then adjusted by varying the current through the output MOSFET with the control logic, while using the output capacitor to smooth out the ripple. Meanwhile, the current through the FB pin is monitored, and if the current exceeds the set threshold, the MOSFET is turned off and the process is repeated every switching cycle.

The L5971D also incorporates an Adaptive Voltage Scaling (AVS) circuit, which is designed to adjust the output voltage dynamically to match the power requirements of the application. By varying the switching frequency and duty cycle, the output voltage can be ramped up or down quickly, improving the overall system efficiency. The AVS also helps to maintain the output voltage at a constant level, while preserving the integrity of the power supply.

In addition, the L5971D offer several protections, including input undervoltage lockout with hysteresis, output overvoltage, overcurrent, and over temperature protection. These protect the application from potentially damaging discharge events and to prevent system shutdowns due to component failure.