9.2.1.2.2 Thermal Considerations

Thermal considerations constrain operation at different input current and voltage levels. The power dissipated inside the ISO121x devices is determined by the voltage at the SENSE pin (V_SENSE) and the current drawn by the device (I_(INx+SENSEx)). The internal power dissipated, when taken with the junction-to-air thermal resistance defined in the Thermal Information table can be used to determine the junction temperature for a given ambient temperature. The junction temperature must not exceed 150°C.

Figure 19 shows the maximum allowed ambient temperature for the ISO1211 device for different current limit and input voltage conditions. The ISO1211 device can be used with a V_SENSE voltage up to 60 V and an ambient temperature of up to 125°C for an R_SENSE value of 562 Ω, which corresponds to a typical current limit of 2.25 mA. At higher levels of current limit, either the ambient temperature or the maximum value of the V_SENSE voltage must be derated. In any design, the voltage drop across the external series resistor, R_THR, reduces the maximum voltage received by the SENSE pin and helps extend the allowable module input voltage and ambient temperature range.

1. This figure also applies to the ISO1212 device if only one of the two channels are expected to be active at a given time.

Figure 19. Maximum Ambient Temperature Derating Curve for ISO1211 vs V_SENSE

Figure 20 shows the maximum allowed ambient temperature for the ISO1212 device for different current limit and input voltage conditions. The ISO1212 device can be used with a V_SENSE voltage up to 36 V and an ambient temperature of up to 125°C for an R_SENSE value of 562 Ω, which corresponds to a typical current limit of 2.25 mA. At higher current limit levels, either the ambient temperature or the maximum value of the V_SENSE voltage must be derated. Operation of the ISO1212 device with an R_SENSE value of 200 Ω and with both channels active is not recommended beyond a V_SENSE voltage of 36 V. In any design, the voltage drop across the series resistor, R_THR, reduces the maximum voltage received by the SENSE pin and helps extend the allowable module input voltage and ambient temperature range.

1. This figure only applies if both channels of the ISO1212 device are expected to be on at the same time. If only one channel is expected to be on at a given time, refer to Figure 19.

Figure 20. Maximum Ambient Temperature Derating Curve for ISO1212 vs V_SENSE