LM78S40N/NOPB

Voltage - Output (Min/Fixed):	1.25V
Base Part Number:	LM78S40
Supplier Device Package:	16-PDIP
Package / Case:	16-DIP (0.300", 7.62mm)
Mounting Type:	Through Hole
Operating Temperature:	-40°C ~ 125°C (TA)
Synchronous Rectifier:	No
Frequency - Switching:	100Hz ~ 100kHz
Current - Output:	1.5A (Switch)
Voltage - Output (Max):	40V (Switch)
Series:	--
Voltage - Input (Max):	40V
Voltage - Input (Min):	2.5V
Number of Outputs:	1
Output Type:	Adjustable
Topology:	Buck, Boost
Output Configuration:	Positive or Negative
Function:	Step-Up, Step-Down
Part Status:	Active
Packaging:	Tube

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Introduction

The LM78S40N/NOPB is a voltage regulator from Texas Instruments that is a member of their DC DC Switching Regulators series. Switching regulators are designed to provide a dual output DC supply with a constant, adjustable voltage, while drawing very low quiescent current when compared to a linear regulator. The LM78S40N/NOPB boasts an exceptionally low quiescent current of only 0.2 μA, making it an excellent choice for energy-conscious applications.

Features

The LM78S40N/NOPB has several features that make it an ideal choice for applications where high efficiency and precise voltage control are necessary. Its output is adjustable from 2.0V to 40V and its switching frequency can be adjusted from 500kHz to 1.8MHz. The device’s typical efficiency ranges from 70% to 85% depending on the output voltage, and can reach 90% efficiency during heavy load conditions. The LM78S40N/NOPB also includes several protection features to ensure safe operation, including over-voltage and over-temperature protection.

Application Field

Because of its low quiescent current, the LM78S40N/NOPB is well-suited to energy-sensitive applications that require precise voltage control. Its adjustable frequency can be tuned to reduce EMI in sensitive applications and its wide output voltage range makes it an ideal choice for a variety of power supply applications. Self-powered USB applications, such as keyboards, medical equipment and consumer electronics, can benefit from the LM78S40N/NOPB’s efficiency and flexibility.

Working Principle

The LM78S40N/NOPB operates on a buck topology and consists of two main parts: the controller and the switching element. The controller uses pulse-width modulation (PWM) to sense the output voltage and adjust the on-time of the buck switch accordingly. The input voltage is applied to the switching element, and is adjusted by the controller to suit the desired output voltage, within the specified range. The LM78S40N/NOPB’s high frequency operation allows for a much smaller form factor than is possible with linear regulators, making it an attractive choice for space-constrained applications. The device also offers an advanced soft-start function to limit inrush currents, making it ideal for applications that require high load current demands without inrush current spikes.

Conclusion

The LM78S40N/NOPB is an ideal voltage regulator for applications where high efficiency and precise voltage control are required. Its exceptional 0.2 μA quiescent current, high efficiency and adjustable switching frequency make it an excellent choice for self-powered USB applications, where space and power restrictions make a linear regulator unsuitable. The LM78S40N/NOPB’s advanced features and wide output voltage range make it a versatile solution for a variety of power supply design needs.

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