Digital lending start-up Blend raised $75 million in fresh funding at a valuation of almost $1.7 billion, a jump of more than 70% from its previous round a year earlier, CNBC has learned. Refinance application volumes jolted more than 1,000% higher in March, and purchase applications climbed by more than 100% every month since May, according to company figures. The Series F funding round was led by Canapi Ventures, a fintech VC fund that is backed by the banking industry and led in part by Gene Ludwig, a former U.S. regulator who founded the Promontory Financial Group.