LM2903-Q1 family consists of a PNP darlington pair input, allowing the device to operate with very high gain and fast response with minimal input bias current. The input Darlington pair creates a limit on the input common mode voltage capability, allowing LM2903-Q1 to accurately function from ground to VCC–1.5V differential input. This is enables much head room for modern day supplies of 3.3 V and 5.0 V.
The output consists of an open drain NPN (pull-down or low side) transistor. The output NPN will sink current when the negative input voltage is higher than the positive input voltage and the offset voltage. The VOL is resistive and will scale with the output current. Please see Figure 3 in the Typical Characteristics, LM2903-Q1 and LM2903E-Q1 Only section for VOL values with respect to the output current.