The operational area of an LDO is limited by the dropout voltage, output current, junction temperature, and input voltage. The recommended area for continuous operation for a linear regulator is shown in Figure 8-3 and can be separated into the following regions:

• Dropout voltage limits the minimum differential voltage between the input and the output (V_IN – V_OUT) at a given output current level; see the Dropout Voltage section for more details.
• The rated output current limits the maximum recommended output current level. Exceeding this rating causes the device to fall out of specification.
• The rated junction temperature limits the maximum junction temperature of the device. Exceeding this rating causes the device to fall out of specification and reduces long-term reliability.
  • Equation 5 provides the shape of the slope. The slope is nonlinear because the maximum rated junction temperature of the LDO is controlled by the power dissipation across the LDO, thus when V_IN – V_OUT increases the output current must decrease.
• The rated input voltage range governs both the minimum and maximum of V_IN – V_OUT.

Figure 8-3 Continuous Operation Diagram With Description of Regions