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 given in Figure 7-3 and is separated into the following parts:
- Dropout voltage limits the minimum
differential voltage between the input and the output (VIN – VOUT)
at a given output current level. See the Dropout Operation section for more details.
- The rated output currents 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.
- The shape of the slope is given by
Equation 4. 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 decreases.
- The rated input voltage range governs
both the minimum and maximum of VIN – VOUT.
Figure 7-3 shows the recommended area of operation for this device on a JEDEC-standard high-K board
with a RθJA, as given in the Thermal Information table.