The back-to-back clamping diodes in the input of the MAX44243 are used to protect the IC. According to page 2 of the datasheet, the absolute maximum rating of all the pins other than voltage supply pin is from (GND - 0.3V) to (VDD + 0.3V). When the MAX44243 input signal is higher than the supply voltage, the diode conducts and clamps the voltage to within the power supply voltage. This provides effective protection for the device.