For the TLV4021 (open-drain output versions of the TLV40x1 family), 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 driven 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 a finite amount of leakage current that needs to be accounted for. Use I_O-LKG from the EC Table and the V_IH minimum from the logic device being driven to determine R_PU maximum using Equation 4.

Equation 4.

Next, determine the minimum value for R_PU by using the V_IL maximum from the logic device being driven. In order for the comparator output to be recognized as a logic low, V_IL maximum is used to determine the upper boundary of the comparator's V_OL. V_OL maximum for the comparator is available in the EC Table for specific sink current levels and can also be found from the V_OUT versus I_SINK curve in the Typical Application curves. A good design practice is to choose a value for V_OL maximum that is 1/2 the value of V_IL maximum for the input logic device. The corresponding sink current and V_OL maximum value will be needed to calculate the minimum R_PU. This method will ensure enough noise margin for the logic low level. With V_OL maximum determined and the corresponding I_SINK obtained, the minimum R_PU value is calculated with Equation 5.

Equation 5.

Since the range of possible R_PU values is large, a value between 5 kΩ and 100 kΩ 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.