LM1771TMMX/NOPB

Application Field and Working Principle of LM1771TMMX/NOPB

The LM1771TMMX/NOPB is part of National Semiconductor’s family of DC/DC switching controllers. It is a voltage regulator product specifically designed for use in portable and small systems, such as mobile phones, digital cameras, and PDAs. The LM1771TMMX/NOPB features low quiescent current, accurate current limit, pulse-by-pulse current foldback protection, and adjustable output voltage. It’s designed to be used as a fixed frequency, dual-channel, step-up regulator for applications that require up to 3A output current.

Features

• 36V Maximum Input Range
• Integrated Power Switch
• Low Quiescent Current
• Accurate Current Limit
• Pulse-by-Pulse Current Foldback
• Adjustable Output Voltage
• Internal Soft Start

Function and Operation

The LM1771TMMX/NOPB is a step-up voltage regulator used to regulate output voltage above the input voltage. It operates in two modes, forced-ON and burst-mode. In forced-ON mode, the output of the regulator is continuously regulated. The input voltage must be within range in order for this to happen. In burst-mode, the regulator switches on for a predetermined amount of time, after which it shuts off for a period to conserve energy. When the load current is reduced, the regulator switches on for a longer period but remains off for a shorter period. This keeps the output voltage within the desired range by compensating for changes in the input voltage as well as the load current.

The regulator’s output voltage is adjusted using an external voltage divider. The output voltage is determined by the voltage at the VCOM pin, which is set using the divider. The regulator’s output can be set to any voltage between 1.8V and the input voltage.

The regulator also features a current limit circuit to protect the load in case of over-current. When the output current rises beyond the set limit, the regulator will shut off, protecting both the load and the regulator. A pulse-by-pulse current foldback feature is provided to reduce the load current if it exceeds the set limit for an extended period of time.

Applications

• Mobile phones
• Digital cameras
• PDA’s
• Portable CD players
• Battery-operated medical devices

Conclusion

The LM1771TMMX/NOPB is an ideal solution for applications that require up to 3A output current and require a regulated output voltage. It features low quiescent current, accurate current limit, pulse-by-pulse current foldback protection, and adjustable output voltage. Its versatility makes it suitable for use in a wide range of applications including mobile phones, digital cameras, PDAs, portable CD players, and battery-operated medical devices.