In the application example shown in Figure 10-8, ISOUSB211 is powered using USB VBUS on the connector side, and a local 3.3-V digital supply on the microcontroller side to generate V_3P3Vx. An external LDO or DC-DC buck converter is used to generate V_1P8Vx on both sides.

In this scenario, the total power consumption from both sides taken together is:

V_BUS1 × I_VBUS1 + V_1P8V1 × I_1P8V1 + V_3P3V2 × I_3P3V2 + V_1P8V2 × I_1P8V2

Assuming 5.25 V as the maximum value of VBUS, and 1.89 V as the maximum value of the external 1.8-V power supply, the internal power dissipation is calculated as

5.25 V×13.5 mA + 1.89 V×96 mA + 3.5 V×13.5 mA+1.89 V×96 mA = 481 mW.

Since the junction-to-air thermal resistance is 44.2°C/W, this power dissipation results in a 22°C internal temperature rise. Ambient temperature up to 128°C can be supported for this configuration.

TLV741P and TLV62568 are examples of low-cost LDO and buck converter respectively that may be used in this application. Both options reduce the power dissipation in ISOUSB211. However, the buck converter additionally reduces power dissipation at the system level, and also the current drawn from VBUS and local 3.3-V supplies.

This configuation offers the lowest power dissipation and the highest ambient temperature operation using external regulators.

Figure 10-7 Using ISOUSB211 with 1.8-V supplied with External Regulators.