LDO, also known as Low Dropout Linear Regulator, is a commonly used power management chip. Its product feature is that it can maintain the stability of the output voltage with a small voltage difference between the input voltage and the output voltage, making it suitable for low-voltage voltage regulation circuits. LDO is commonly used in power supply and battery products to reduce the slightly high voltage of the power source to a lower stable voltage circuit application.

1 What are the characteristics of LDO products?
As a highly integrated product, a major feature of LDO is that it saves a lot of peripheral components, has fast load adjustment speed, and is easy to apply. LDO has the advantages of low power consumption, high precision, low noise, high efficiency, and fast transient response. LDO adopts a linear voltage regulation method, which is more energy-efficient and has low product power consumption. It usually has high power suppression ratio and low noise characteristics, making the product very suitable for scenarios that require low noise, such as low load current, low voltage drop step-down circuits, low-power circuits, and low-noise circuits.

Usually, LDO's job is like this. The VIN terminal is provided to the output terminal VOUT through a MOS transistor, and the error amplifier compares the output voltage with a reference voltage source through a feedback network, and adjusts the gate voltage of the MOS transistor to maintain stable output voltage. Compensation circuits can be integrated into error amplifiers to ensure stability.

Usually, there are two types of LDOs: PMOS LDO and NMOS, each with its own advantages and disadvantages.

PMOS LDO has the advantages of high output voltage stability, small voltage difference, high efficiency, wide applicable voltage range, good noise isolation effect, high reliability, and long lifespan, which have made it widely used in aerospace, automotive, industrial, and consumer electronics fields.

1/High output voltage stability
The output voltage stability of PMOS LDO is very high, thanks to its internal negative feedback system. When the output voltage increases, the feedback voltage (VOUT obtained by dividing two resistors) also increases, and the output voltage of the error amplifier increases, thereby adjusting the gate voltage of the PMOS transistor, reducing its output current and voltage, and forming a stable negative feedback loop.

2/Small pressure difference, high efficiency

The voltage difference (difference between input voltage and output voltage) of PMOS LDO is relatively small, which means that under the same output current, the power consumption of PMOS LDO is lower and the efficiency is higher. This is particularly important for devices that require long-term operation and have strict requirements for power consumption.

3/Wide applicable voltage range

PMOS LDO works very stably when the transmission power supply voltage is higher than the output power supply voltage. This enables PMOS LDO to operate normally over a wide range of input voltages, providing greater flexibility for different application scenarios.

5/Good noise isolation effect

PMOS LDO has excellent noise isolation performance, with the specific indicator being power supply rejection ratio (PSRR). PSRR represents the ratio of output noise to input noise, and LDO with high PSRR can more effectively filter out noise from the input terminal, providing clean power for sensitive circuits.

4/Moderate output current capability

Although the on resistance of PMOS is relatively high, resulting in significant switching losses, its output current capability is moderate and sufficient to meet the needs of many application scenarios. Meanwhile, due to its high output voltage stability, it can maintain the stability of the output voltage even when the load changes. PMOS LDO has high reliability and long lifespan, and its internal PMOS transistor and other components are carefully designed and manufactured to operate stably for a long time in harsh environments.

NMOS LDO has the advantages of fast transient response, low static current, high current driving capability, wide voltage regulation range, and good stability, making it widely applicable in the field of power management, especially in applications that require fast response and high efficiency.

1/Fast transient response
The unit gain bandwidth of NMOS type LDO is relatively large, therefore it has excellent transient response capability. This means that when the load current or input voltage changes, the NMOS LDO can quickly adjust the output voltage and maintain stability.

2/Low static current:
When the load current changes, the static current of NMOS LDO remains almost unchanged. This is because NMOS only uses voltage signal control, and the voltage signal does not need to consume the current of the error amplifier itself. Therefore, NMOS LDO can reduce power consumption while maintaining stable output voltage.

3/Wide voltage regulation range:
NMOS LDO can operate normally within a wide input voltage range and provide stable output voltage. This makes NMOS LDO suitable for power systems of different voltage levels.

4/High current driving capability:
Due to the higher electron mobility of NMOS compared to PMOS, NMOS LDO has a smaller layout area when driving the same current, resulting in higher current driving capability. This makes NMOS LDO suitable for applications that require high current output.

5/Good stability:
The loop stability of NMOS LDO is good, thanks to the design of its internal negative feedback system. When the output voltage changes, the negative feedback system will quickly adjust the gate voltage of the NMOS transistor to maintain the stability of the output voltage.

Heketai reminds customers that when choosing NMOS or PMOS LDO, they should consider input and output voltage differences, power consumption requirements, and response speed design complexity. The appropriate one is the best.

2、 Application areas of LDO products

The common applications of LDO products include communication, computer, industrial control, medical, consumer electronics, automotive, etc.

Typical application circuit
Mobile devices: LDO provides stable power supply for microprocessors, memory, and other low-power components in smartphones, ensuring the normal operation of devices and extending battery life. Tablets also require LDO to provide stable power supply to support their high-performance processors and graphics processors.
Automotive Electronics: LDO provides stable power supply for in car information systems, ensuring the normal operation of navigation, entertainment, and other functions. In automotive electronic safety systems, LDO provides stable power supply for sensors and actuators, supporting the safety performance of vehicles.
In the field of industrial control, LDO is used in automation equipment to provide stable voltage sources for sensors, microcontrollers, and other critical components, ensuring precise control and stable operation of the equipment. LDO provides stable power supply for circuits and components in industrial control systems, supporting real-time monitoring and data acquisition of the system.
In the field of medical equipment, LDO provides stable power supply for precision measuring instruments in medical devices, ensuring the accuracy and reliability of measurement results. In portable blood gas analyzers, blood pressure monitors, electrocardiographs, and other products, LDO provides low-noise, high-precision power output for these devices to ensure their normal operation and patient safety.
In the field of consumer electronics, LDO provides stable power supply for portable media players, ensuring smooth playback of audio and video content. It provides stable power supply for wireless communication modules such as Bluetooth and Wi Fi modules, and supports wireless connection and data transmission of devices.
It can also be used in communication devices such as wireless base stations, routers, and switches, and LDO can provide low-noise power to ensure signal integrity. In the field of smart homes and IoT devices, LDOs also play an important role in these devices, providing stable power supply for components such as sensors, controllers, and actuators.
LDO products have a wide range of applications in multiple fields and have a very broad market prospect. With the rapid development of technology, emerging technologies such as cloud computing, big data, and artificial intelligence have put forward higher requirements for power management. As an important component of power management, the stability and reliability of LDO products are crucial for the operation of the entire system. Therefore, the development of these emerging technologies will drive further growth in the LDO product market. In the coming years, the LDO product market will continue to maintain a rapid growth trend.