7.4.3 Dropout Operation

If the input voltage is lower than the nominal output voltage plus the specified dropout voltage, but all other

conditions are met for normal operation, the device operates in dropout mode. In this mode, the output voltage

tracks the input voltage. During this mode, the transient performance of the device becomes significantly

degraded because the pass transistor is in the ohmic or triode region, and acts as a switch. Line or load

transients in dropout can result in large output-voltage deviations.

When the device is in a steady dropout state (defined as when the device is in dropout, VIN < VOUT(NOM) + VDO,

directly after being in a normal regulation state, but not during start up), the pass transistor is driven into the

ohmic or triode region. When the input voltage returns to a value greater than or equal to the nominal output

voltage plus the dropout voltage (VOUT(NOM) + VDO), the output voltage can overshoot for a short period of time

while the device pulls the pass transistor back into the linear region.

7.4.4 Disabled

The output of the device can be shutdown by forcing the voltage of the ON/OFF pin to less than the maximum

ON/OFF pin low-level input voltage (see the Electrical Characteristics table). When disabled, the pass transistor

is turned off, internal circuits are shutdown, and the output voltage is actively discharged to ground by an internal

discharge circuit from the output to ground.

www.ti.com

LP2985

SLVS522Q – JULY 2004 – REVISED DECEMBER 2022

Copyright © 2022 Texas Instruments Incorporated

Submit Document Feedback

19

Product Folder Links: LP2985