RT8108FGSP Integrated Circuits (ICs)

Series:	--
Packaging:	Tape & Reel (TR)
Part Status:	Discontinued at Digi-Key
Output Type:	Transistor Driver
Function:	Step-Down
Output Configuration:	Positive
Topology:	Buck
Number of Outputs:	1
Output Phases:	1
Voltage - Supply (Vcc/Vdd):	4.75 V ~ 13.2 V
Frequency - Switching:	500kHz
Duty Cycle (Max):	85%
Synchronous Rectifier:	Yes
Clock Sync:	No
Serial Interfaces:	--
Control Features:	Enable, Phase Control
Operating Temperature:	-40°C ~ 85°C (TA)
Package / Case:	8-SOIC (0.154", 3.90mm Width) Exposed Pad
Supplier Device Package:	8-SOP

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RT8108FGSP Application Field and Working Principle

The RT8108FGSP application field covers a wide range of power management ICs (also known as PMICs) - Voltage Regulators, DCDC Switching Controllers and Buck Converters. The RT8108FGSP is a step-down switching controller with extensive features specifically designed to maximize efficiency and provide high current output. It operates in constant frequency, current mode and is ideal for powering high-performance applications.

Overview

The RT8108FGSP is a constant current, voltage mode, step-down converter capable of driving up to 3A of continuous current from a power supply voltage of 3.0V to 18V. The device operates in a constant frequency current mode and is capable of providing excellent efficiency of up to 90% at light load levels. It is capable of operating at switching frequencies up to 1MHz, thus providing fast response to dynamic load conditions. The output voltage is normally programmed via external resistors to the desired voltage level without the need for external switching elements. A few external components are necessary to complete the application circuit for hard-wired or adjustable output voltage. The note provides a detailed description of the application circuit and its related components.

Internal Circuitry

The RT8108FGSP consists of two main functional blocks: an internal oscillator to generate a fixed frequency clock signal and a current mode control loop including an error amplifier, a voltage reference and a high side drive circuit. The oscillator generates a fixed frequency clock signal which is used for both the switching controller and the internal linear regulator. The internal linear regulator is used to set the reference voltage for the error amplifier and the voltage reference. The current mode controller uses an internal error amplifier, a voltage reference and an internal comparator to regulate the output voltage. The error amplifier provides a voltage gain proportional to the load current and monitors the output voltage. If the voltage feedback signal is higher than the voltage reference, the internal comparator will trigger the high side gate drive to turn off. When the voltage feedback signal is lower than the voltage reference, the comparator will turn off the high side gate drive and the low side gate drive will be enabled. The result is that the output voltage is regulated to the target voltage level.

Power Dissipation

The RT8108FGSP has very low power dissipation due to its high efficiency of up to 90% at light load levels. The internal circuitry is designed for high switching frequency operation, thus providing fast response to dynamic load conditions, enabling tight accuracy and high output current. The device has a low power operation mode for power saving in idle modes.

Protection Features

The RT8108FGSP prevents system failure due to short-circuits, under and over-voltages, and over-temperature conditions. It has an over-current protection circuit which ensures continual output current against over-load and prevents further damages. The integrated over-temperature protection circuit is also included to ensure safe operation of the device.

Conclusion

The RT8108FGSP is a high performance step-down switching controller capable of delivering up to 3A of current in an extended voltage range. It operates at a fixed frequency and utilizes an internal Linear Regulator, Error Amplifier and Comparator to regulate the output voltage. It is ideal for powering high performance applications and its features include low power dissipation, protection features and a low power mode.

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