6.4 Device Functional Modes

Table 6-1 shows the conditions that lead to the different modes of operation. See the Electrical Characteristics

table for parameter values.

Table 6-1. Device Functional Mode Comparison

OPERATING MODE

PARAMETER

VIN

VON/OFF

IOUT

TJ

Normal operation

VIN > VOUT(nom) + VDO and VIN > VIN(min)

VON/OFF > VON/OFF(HI)

IOUT < IOUT(max)

TJ < TSD(shutdown)

Dropout operation

VIN(min) < VIN < VOUT(nom) + VDO

VON/OFF > VON/OFF(HI)

IOUT < IOUT(max)

TJ < TSD(shutdown)

Disabled

(any true condition

disables the device)

VIN < VUVLO

VON/OFF < VON/

OFF(LOW)

Not applicable

TJ > TSD(shutdown)

6.4.1 Normal Operation

The device regulates to the nominal output voltage when the following conditions are met:

• The input voltage is greater than the nominal output voltage plus the dropout voltage (VOUT(nom) + VDO)

• The output current is less than the current limit (IOUT < ICL)

• The device junction temperature is less than the thermal shutdown temperature (TJ < TSD)

• The ON/OFF voltage has previously exceeded the ON/OFF rising threshold voltage and has not yet

decreased to less than the enable falling threshold

6.4.2 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.

6.4.3 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.

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LP2992

SNVS171L – NOVEMBER 2001 – REVISED FEBRUARY 2025

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