The APDO, T2P pins are active low, open-drain outputs which give an indication about the PSE allocated power. Optocouplers can interface these pins to circuitry on the secondary side of the converter. A high-gain optocoupler and a high-impedance (for example, CMOS) receiver are recommended. Please see the as an example circuit. Below is an example design calculation.

1. Let V_CC = 12-V, V_OUT = 5-V, = 10-kΩ, V_TPx-OUT (low) = 400-mV maximum.
   1. I_TPx-OUT = 0.46 mA.
2. The optocoupler CTR will be needed to determine . A device with a minimum CTR of 300% at 5-mA LED bias current is selected. CTR will also vary with temperature and LED bias current. The strong variation of CTR with diode current makes this a problem that requires some iteration using the CTR versus I_DIODE curve on the optocoupler data sheet.
   1. The approximate forward voltage of the optocoupler diode is 1.1 V from the data sheet.
   2. I_TPx-MIN = 1 mA and R_TPx = 10.6 kΩ.
3. Select 10.7-kΩ resistor.