BD3989FV-E2

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Application Field and Working Principle of BD3989FV-E2

Introduction

The BD3989FV-E2 is a low drop-out (LDO) regulator of the three-terminal regulator series produced by Rohm Semiconductor. It is a linear voltage regulator that allows for the conversion of a higher voltage to a lower output voltage with a high degree of accuracy. The main features and functions of the BD3989FV-E2 include low output voltage noise, over-voltage protection (OVP) detection, over-current protection (OCP) detection, short-circuit protection (SCP) monitoring, low quiescent current, and low standby current. This is an ideal choice for applications such as communication devices and automotive electronics.

Application Field

The BD3989FV-E2 is regularly used in communication devices such as cellular phones and wireless modules, as well as in automotive and industrial applications. In automotive applications, BD3989FV-E2 can be used as a pre-regulator of a single Li-ion cell power supply, with its high precision adjustable output voltage, over-voltage protection, and thermal protection for optimal protection against faults and derangements.

Features and Benefits

• The output voltage is adjustable through external software or hardware.
• The operating temperature range is –40°C to +85°C.
• The signal-to-noise ratio of the output is maintained even at low frequencies.
• Over-current protection and over-voltage protection are included.
• Low quiescent current and low standby current for maximum efficiency.
• Short-circuit protection is embedded.
• Built-in thermal protection against excessive temperatures.

Working Principle

Also known as a "low drop out linear regulator", the BD3989FV-E2 is a three-terminal regulator with a bandgap reference voltage source, voltage error amplifier, PNP pass transistor, and several protection circuits. The incoming power is converted to an adjustable output voltage by the LDO. The application of a reverse polarity voltage to the input terminal or a short circuit between the output and input terminals does not result in damage to the regulator.

The BD3989FV-E2 receives an input voltage through the VIN terminal, which is controlled by the error amplifier before being converted to the output voltage. The difference in potential between IN and OUT is called the drop-out voltage. The drop-out voltage of the BD3989FV-E2 is typically 1.2 V. When the input voltage falls below the output voltage plus the drop-out voltage, the regulator will no longer be able to provide a regulated output voltage.

The over-current protection circuit prevents any damage to the regulator as a result of high current. During excessive current operations, the over-current protection circuit monitors the voltage drop across the shunt resistor, and when the voltage drop is higher than a set limit, the protection circuit pulls the RESET terminal low until the load current is reduced. The over-voltage protection circuit is a comparator that checks the output voltage continuously. When the output voltage is higher than a preset trip voltage, the over-voltage protection circuit pulls the RESET terminal low to reduce the output voltage.

The thermal protection circuit monitors the temperature of the internal semiconductor die. This protection circuit is an open-drain transistor that will be active when the die temperature becomes higher than a preset temperature of +165°C. In this case, the RESET terminal is pulled low, and the device goes into a protection state.

Conclusion

The BD3989FV-E2 is a three-terminal low drop-out linear regulator from Rohm Semiconductor. Its features of high precision adjustable output voltage, over-voltage protection, and thermal protection make it suitable for use in communication and automotive applications. Its working principle of converting a higher voltage to a lower output voltage employs a bandgap reference voltage source, voltage error amplifier, PNP pass transistor and protection circuits.

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