Bobby, whose biggest hit is the classic "What You Won't Do for Love," died in his sleep Tuesday night at home in New Jersey, according to his rep.

The singer/songwriter hadn't been able to walk for about 5 years as he coped with painful bouts of neuropathy and a torn tendon in his ankle. Last year his team revealed Bobby had a bad reaction to a prescribed antibiotic in 2017 -- they say it caused his Achilles tendon to rupture, which led to the neuropathy.

Caldwell dropped his signature hit in 1978 ... when it reached the top 10 on Billboard, and made his self-titled debut album go double platinum.

If you're of a certain age, you know every line of 'Do for Love,' and the song is so enduring you hear someone sing it practically every season on "American Idol" and "The Voice."

It's also been covered by countless artists -- including Boyz II Men, Snoh Aalegra and Michael Bolton -- and Tupac Shakur heavily sampled it for his song, "Do For Love."

Bobby also wrote songs for the likes of Neil Diamond, Al Jarreau, Roberta Flack and Boz Scaggs. He even penned the 1986 #1 hit, "The Next Time I Fall" for Amy Grant and Peter Cetera.

Bobby was 71.