The billionaire investor‘s back on the Twitter and CNBC trail today. He said in a tweet this morning that, over the last two weeks, he bought $500M in Apple’s shares, bringing his total to more than $3B. Carl Icahn“Since tweeting about our large position in [Apple] on August 13, when the stock was $468 per share, we’ve kept buying shares of this ‘no brainer’,” he said. Shares closed yesterday at $549.07. Still, he put the company on notice that he’s about to release what he calls an “in-depth letter” as part of his campaign to pressure CEO Tim Cook and the board to increase share repurchases. “We feel [Apple’s] board is doing great disservice to shareholders by not having markedly increased its buyback,” Icahn says. He filed a shareholder proposal for a vote on the issue at the company’s next annual meeting. “I’m not against the management of this company,” he told Time for a cover story that ran last month. But with $147B “they’ve just got too much money on their balance sheet.” He’ll likely expand on that mid-day when he appears on another of his favorite venues: CNBC. Apple shares are up 1.4% in late morning trading.