American Well, a start-up that helps hospitals and other physician groups integrate virtual consultations, has backing from a giant new partner: Philips.

As of June 28, American Well had raised a fresh $291 million, according to an SEC filing, which indicates the company is aiming to raise a total of about $315 million. In January, American Well announced a deal with Philips "to jointly deliver virtual care solutions around the world." Derek Ross, the business leader of Philips's population health management division, has joined American Well's board as part of his company's investment in the start-up.

The new infusion of capital makes American Well one of the best-funded companies in the booming digital health space. Telemedicine, or remotely connecting patients with doctors through secure voice and video chats, has long been considered one of the biggest opportunities to infuse technology into medicine.

However, adoption has been slow because of regulatory concerns along with a lack of consumer awareness and the challenges that many physicians have pulling in all the necessary patient records.

Still, investors are betting on the opportunity. American Well competes with Teladoc, a public company, and Doctor on Demand, a venture-backed consumer app that also offers virtual physician visits.