11.2.1.2.2 Output Voltage and Logic Input Level

In order for ATL431LI to properly be used as a comparator, the logic output must be readable by the receiving logic device. This is accomplished by knowing the input high and low level threshold voltage levels, typically denoted by V_IH and V_IL.

As seen in Figure 24, ATL431LI's output low level voltage in open-loop/comparator mode is approximately 2 V, which is typically sufficient for 5V supplied logic. However, would not work for 3.3 V and 1.8 V supplied logic. To accommodate this a resistive divider can be tied to the output to attenuate the output voltage to a voltage legible to the receiving low voltage logic device.

ATL431's output high voltage is equal to V_SUP due to ATL431LI being open-collector. If V_SUP is much higher than the receiving logic's maximum input voltage tolerance, the output must be attenuated to accommodate the outgoing logic's reliability.

When using a resistive divider on the output, be sure to make the sum of the resistive divider (R1 and R2 in Figure 23) is much greater than R_SUP in order to not interfere with ATL431LI's ability to pull close to V_SUP when turning off.