The AT73C224-x is a family of ultra low cost Power Management Unit, available in a small outline QFN 5x5mm package. The AT73C224-x family is optimized for portable applications, typically powered by a Li-Ion battery. The AT73C224-x device is also suitable to operate from a standard 3.3V to 5.25V voltage rail. It includes four power supplies and a very low power Realtime Clock (RTC). In normal mode (main battery present), the backup battery is recharged through a 2.6V RTC LDO. The AT73C224-x series offer different automatic start-up sequences (with varying orders of power-on and specific default output values) and different soft management modes: dynamic (via SPI or TWI) with register access or static, with access to power on/off of the four power supplies. Each AT73C224-x device is equipped with a very low power bandgap reference, low power 32 kHz and 1 MHz oscillators and an internal LDO used to generate the internal supply (VINT) equal to 2.8V. Auxiliary cells, such as a power-on reset (POR) and a voltage monitor are used to control the system power-on (battery plugged in) and power-off (battery unplugged). The four power supplies are named: BOOST1, BUCK2, LDO3 and LDO4. Table 1-1 lists the different devices available in the AT73C224-x series.