Application design of high current low saturation secondary linear regulator LDO

As the whole equipment is becoming increasingly miniaturized and power-saving, low-loss linear regulators (LDOs) with low power consumption are becoming the mainstream in the market of linear regulators for switching power supplies . In order to achieve high performance and high speed, the microcomputer or digital signal processor (DSP) technology used in the equipment has made rapid progress and development every year. At the same time, the power supply voltage that is essential for these microcomputers or digital signal processors is also getting lower and lower. In addition, the voltages corresponding to different manufacturing processes are different, so a variety of power supply voltages are required. To solve this problem, various manufacturers have begun to use new technologies to set the intermediate voltage in the switching power supply and use LDO regulators to provide LSI power. On the other hand, high-current LDO regulators are also used in battery devices to maximize the effective use of battery voltage.





The power supply architecture currently commonly used is to first use a DC/DC converter to obtain a voltage of about 5V from a high input power supply, and then use a linear regulator to step down the voltage to a voltage of 3.3 to 1.0V. This type of regulator is called a secondary linear regulator, and it provides a more stable power supply at a low input voltage near devices that require this type of power architecture. The BD□□KA5 series developed by ROHM is suitable as this type of secondary linear regulator (Figure 1).



While striving to save more space and be more stable, the secondary regulator continues to improve its high accuracy, which is necessary to adapt to the narrow input voltage range of components such as DSP. Although the current capacity of the BD□□KA5 series is only 500mA, the output phase compensation capacitor can support a small ceramic capacitor of 1μF , saving the space occupied by the regulator. At the same time, by adopting ROHM's proprietary trimming technology, the output voltage accuracy is improved by ±1%. In addition, by using a P-channel MOS transistor as the transistor for driving the output, the circuit current can be controlled even if the load current increases , which is beneficial to thermal design. The power input range is 2.3V-5V, which is most suitable for 3.3V and 5V series power input. In addition, the output voltage specifications include 1.0V, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, adjustable input type and low voltage output, etc., and the products can meet various different needs. On the other hand, standard fixed output and adjustable output that directly obtain output voltage from the battery are still indispensable, and their output current peak increases year by year. ROHM's BA□□DD0 series is an LDO with 2A current capacity (Figure 2). While achieving a high output current of 2A, this series improves the accuracy of the output voltage by ±1% and achieves a low voltage drop of 0.5V. Corresponding to the change of input voltage, it avoids the output voltage from dropping to the low input voltage limit and ensures the output startup in the low voltage state. In addition, the pin configuration is compatible with the industry standard 78 series and ROHM's previous 1A low saturation regulator, which is easy to replace. The input voltage range is very wide (3 to 25V), and the output voltage range also ranges from 1.5V, 1.8V, 2.5V, 3.0V, 3.3V, 5.0V, 9.0V, 12V to 16V. In order to reduce the power consumption of the non-working parts of the whole equipment, power management is implemented in each area to cut off the power supply. All models of the BD□□KA5 series and BA□□DD0 series have a shutdown switch function that interrupts all lines according to external logic. The current consumption in standby is 0μA (typical value), which is conducive to low-power design. Both series of LDO regulator products have built-in protection circuits as follows: 1. Overcurrent protection circuit. Automatic fallback protection circuit is adopted. If the overcurrent protection circuit starts to work and the output voltage drops, the output current is more concentrated. Therefore, compared with the droop protection circuit, the heat loss of the chip in abnormal state such as short circuit can be controlled to 1/3 to 1/5 of the original (see Figure 3). 2. Temperature protection circuit. The temperature protection circuit automatically stops output when the chip temperature exceeds Tj=150℃, preventing damage to the chip caused by excessive temperature, thereby protecting the chip. If the chip temperature drops, there is a hysteresis width to restore the output (Figure 4). 3. Overvoltage protection circuit. The overvoltage protection circuit is only built into the BA□□DD0 series products. If a surge of more than 25V appears in the output, the protection circuit will start to improve the voltage resistance of the internal components of the chip. Even if the input voltage exceeds 50V, it can prevent damage to the chip (Figure 5). 4. High electrostatic withstand voltage. The output electrostatic withstand voltage is the human body discharge mode, which can reach more than 6KV, and has high reliability in any environment.