Toshiba Corp's board on Friday approved plans to make its core chip business a separate company and seek outside investment in it, aiming to avoid being crippled by an upcoming multi-billion dollar writedown for its U.S. nuclear business. Toshiba estimates the value of its chip business – the world's biggest NAND flash memory producer after Samsung Electronics – at 1-1.5 trillion yen ($9-13 billion), a person with direct knowledge of the matter has told Reuters. The partial sale of its chip business would provide a lifeline for Toshiba as a massive charge could wipe out shareholders equity at the end of the financial year in March.