Binance Coin (BNB) is facing a key resistance level at $640 as it attempts to break out and sustain its upward momentum.BNB has recorded a 3% gain in the past 24 hours, reaching its highest price since February 24.Technical indicators, such as the RSI and MACD, suggest strong buying momentum for BNB.If BNB continues its current momentum, it could reach $700 or even $750, but failure to hold above the trendline may result in a decline to $555.