(MarketWatch.com) Shares of Nvidia Corp. plunged on heavy volume on Thursday, after two Wall Street analysts swung to rare bearish ratings on the graphics chip maker, citing concerns over valuation and a tempered outlook for gaming.Analyst Romit Shah at Instinet downgraded Nvidia to reduce from buy. Shah also slashed his stock price target to $90, which is 10% below current levels, after raising it to $100 from $80 just two weeks ago.BMO Capital analyst Ambrish Srivastava dropped his rating to underperform, after being at market perform for at least the last 2 1/2 years. He cut his stock price target to $85, or 15% below current levels, after raising it to $100 from $75 less than three weeks ago.Nvidia (NVDA) Daily Chart(click to enlarge)Double Top:- From the daily chart, we can see that price is forming a double top after failing to break above 120.45 twice. - If price falls below 99.00, NVDA would have completed a double top. - It should also be noted that the RSI is falling below 40, which reflects a loss of the prevailing bullish momentum.- This would put the 90 and even 80 handle in sight.- But, for now, I would limit the bearish outlook to 80. It would satisfy a conventional breakout projection. This conventional breakout projection would take the width of the range, and project it into the direction of the breakout from the point of breakout. In this case, 80 would be that breakout projection.