According to the data sheet http://datasheets.maxim-ic.com/en/ds/MAX1908-MAX8765A.pdf http://datasheets.maxim-ic.com/en/ds/MAX1908-MAX8765A.pdf "D2 protects the

According to the data sheet http://datasheets.maxim-ic.com/en/ds/MAX1908-MAX8765A.pdf http://datasheets.maxim-ic.com/en/ds/MAX1908-MAX8765A.pdf "D2 protects the MAX1908/MAX8724/ MAX8765/MAX8765A when the DC power source input is reversed. A signal diode for D2 is adequate because DCIN only powers the internal circuitry."