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 illustrated 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 (VIN – VOUT)
at a given output current level; see the Dropout Mode 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.
- Figure 8-3 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 VIN –
VOUT increases the output current must decrease.
- The rated input voltage range governs both the minimum and maximum of VIN – VOUT.