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

IOUT

TJ

Normal operation

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

IOUT < IOUT(max)

TJ < TSD(shutdown)

Dropout operation

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

IOUT < IOUT(max)

TJ < TSD(shutdown)

Disabled

(any true condition

disables the device)

VIN < VUVLO

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)

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 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 overshoots for a short period of time

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

6.4.3 Disabled

The device output is disabled if VIN is less than the UVLO voltage, or if the device junction temperature exceeds

the thermal shutdown threshold. See the Electrical Characteristics table for more details regarding the UVLO

voltage thresholds and thermal shutdown. When disabled, the pass transistor turns off and internal circuits shut

down. The output voltage is also actively discharged to ground by an internal discharge circuit from the output to

ground.

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LM1117-Q1

SBVS468A – DECEMBER 2024 – REVISED JUNE 2025

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