A system requires a consistent power supply to operate efficiently. A power management unit has an important role in governing power functions. Depending on the requirements, a system may require high voltage PMU. There are many characteristics of power supply. One of these characteristics is efficiency which determines the following in the system: Thermal loss Electrical loss Amount of cooling required It also determines: Power supply physical package size Final system power supply Operating temperatures of system components System reliability All these factors play a role in determining field support, hardware support and total system cost. There is an interrelation between operating temperature, reliability and efficiency. Power supply can reliably handle certain output load current. This output load current is affected by the ambient operating temperature. Protecting the Supply Characteristics that protect the supply impact power supply operation. These characteristics include: Overcurrent Overcurrent occurs when the output load current is larger than the intended. There are internal protection circuits to protect the system from overcurrent. The power supply’s maximum current capability limits overcurrent. This overcurrent can damage the power supply by causing overheating. It can also damage interconnects such as cables and printed circuit board traces. Therefore, a power supply must have overcurrent protection which is activated when the output current is higher than the maximum. Overtemperature The power supply has a specified value of temperature. The temperature should not be above that value. It can lead to power-supply failure. In addition to damaging the power supply, over temperature can damage associated circuits as well. Power supplies use temperature sensors and associated circuits to detect over temperature and disable supply when the temperature exceeds that value. Semiconductors should not be exposed to temperatures above specified limits. Semiconductors in power supplies are highly vulnerable to overtemperature. Overvoltage Overvoltage occurs when the output voltage exceeds a specified DC value. This can damage the load circuits. Up to 20% overvoltage does not cause permanent damage to an electric system. The right supply can minimize the risk of overvoltage. Power supplies come with overvoltage protection to turn off in case overvoltage occurs. Soft Start When a new board is hot plugged or power is applied for the first time, it may be required to limit inrush current. A soft-start circuit controls rise of current in the beginning before the normal operation. If this current is not controlled, there can be a high peak charging current. This current impacts the output voltage. Undervoltage Lockout When it reaches the required input voltage, UVLO or Undervoltage lockout turns on the power supply. It turns off the power supply, when the input voltage is below a certain level. Power supplies operating from battery power or utility power come with this feature. In case it is battery-powered, when the battery is too discharged to operate, UVLO disables the power supply and the system. Electromagnetic Compatibility (EMC) It involves techniques to minimize EMI. If it is a switch-mode power supply, DC voltage is converted to a pulsed waveform. It generates narrow-band noise (EMI). Radiation must be minimized to contain the noise. Manufacturers enclose it in a box to minimize EMI radiation.