To help ensure reliable operation at data rates and supply voltages, adequate decoupling capacitors must be located as close to supply pins as possible. The input supply must have an appropriate current rating to support output load and switching at the maximum data rate required by the end application. For more information, refer to the Detailed Design Procedure section.

ISOW7821 integrates a synchronous, isolated DC/DC converter along with isolated data channels. Due to finite efficiency of the integrated micro-transformer, for any given output load current, the input current will be proportionally higher. Thus, the input supply (V_CC) decoupling capacitor also needs to be sufficiently larger than the output supply (V_ISO) decoupling capacitor. It is recommended to have an input capacitor that is larger than the output capacitor by at least 100 µF. It is also recommended to have an input power supply to ISOW7821 with sufficient current limit to support output load current requirements. For an output load current of 130 mA, it is recommended to have >600 mA of input current limit and for lower output load currents, the input current limit can be proportionally lower. When the input supply is lower than 2.7 V, the device can go into a protected under-voltage lock out (UVLO) state per the UVLO thresholds specified in datasheet. Under UVLO state, it is recommended that the output voltage also be discharged to less than 2.1 V. This can be accomplished by having an input capacitor that is 100 µF larger compared to the output capacitor. It also helps to have a small load (~10 mA) at the output capacitor to bleed off any unwanted, residual charge. To make sure ISOW7821 quickly transitions from UVLO state to powered state, it is recommended to have an input supply rise time of less than 10 ms.

If it is not possible to follow the aforementioned recommendations and frequent brownouts are expected on the input supply, then simple secondary side monitoring, protection and reset components can help improve the robustness of overall system and power-up or reset mechanisms. More details on output monitoring, protection and an example of reset mechanism can be found in Overvoltage protection for isolated DC/DC converter.