8.2.3.1 Pull-Up Resistor Selection

For the TLV4082 (open-drain outputs), care should be taken in selecting the pull-up resistor (R_PU) value to ensure proper output voltage levels. First, consider the required output high logic level requirement of the logic device that is being drive by the comparator when calculating the maximum R_PU value. When in a logic high output state, the output impedance of the comparator is very high but there is finite amount of leakage current that needs to be accounted for. Use the | I_lkg(OD)| from the EC table and the V_{IH (min)} of the logic device being driven by the TLV4082 to determine R_PU using Equation 10 .

Equation 10.

Next determine the minimum value for R_PU by using the V_{IL (max)} of the logic device being driven by the TLV4082. In order for the comparator output to be recognized as a logic low, V_{IL (max)} is used to determine the upper boundary of the comparator's V_OL. V_{OL (max)} for the comparator is available in the EC table from specific sink current levels and can be found from the V_OUT versus I_SINK curve in the Typical Applications curve. A good design practice is to choose a value for V_OL that is ½ the value of V_IL for the input logic device. The corresponding sink current and V_OL value will be needed to calculate the minimum R_PU. This method will ensure enough noise margin for the logic low level. With i_SINK determined and the corresponding R_PU obtained, the minimum ) is calculated with Equation 11.

Equation 11.

Since the range of possible R_PU values is large, a value between 5 kΩ and 100kΩ is generally recommended. A smaller R_PU value provides faster output transition time and better noise immunity, while a larger R_PU value consumes less power when in a logic low output state.