RE024

RE024 is a dual mode Low Drop Out (LDO) voltage regulator macrocell with a fixed2.8V output voltage, rated for loads up to 160 mA in full power mode and 5 mA in lowpower mode. (Both modes can be selected by the LP2 signal.) RE024 is designed to beintegrated with other analog cells, digital logic,microcontrollers, DSP cores and mem-ory blocks into system-on-chip products.

The circuit RE024 consists of a PMOS pass device, an error amplifier and a feedback resis-tive network, sized to achieve the required closed loop gain. These blocks ofRE024 make upthe regulating loop. An over-current and short circuit protection circuit has beenincluded to limit the output current delivered by the regulator, thus avoiding destructionin case of a short circuit.

An external reference voltage VBG (bandgap voltage) RE024 is necessary for correct function-ality. The target reference voltage is 1.231V delivered, for example, by BG019. Doublepads on the supply voltage VBAT2C/VBAT2CC and output voltage VMEMA/VMEMAA are usedto reduce the total output resistance. Current reference of RE024 is generated inside the cellthrough a circuit supplied by a 2.5V ± 0.1V of regulated input voltage on VSAUVC.

Remote sense terminal VMEMS provides regulation of the load by connecting RE024 to theoutput terminal near a critical point to improve performance of the regulator (e.g., con-necting RE024 to the package pin by double-bonding, thus avoiding the bonding resistanceinfluence). A ceramic capacitor of 2.2 µF connected from VMEMA/VMEMAA to ground isneeded as external compensation.

A low-leakage current switch of RE024 has been added to charge a second external capacitor(2.2 µF - 10 µF) to VMEMA/VMEMAA. This voltage, called VBACKUP , is used to guarantee30 minutes of operation time for the internal system clock and calendar in backupmode when the main battery is unplugged.