Power supplies for microprocessor systems are often complicated by the need to take care of the special requirements of non-volatile read/write memory. Where battery backup CMOS RAMs are used, for example, it is important to ensure that the RAMs are disabled when the primary supply is removed.And when shadow-type NV memory is included the backup transfer must be initiated andcompletedwhen the supplyis interrupted.Designed specifically for such applications, the SGS-THOMSON Microelectronics L4901, and L4902 dual voltageregulatorscombine two5 Vregulatorsplus a reset circuit ona single chip,simplifying the designer’s task.