7.3.5 Output Pulldown

The new chip has an output pulldown circuit. The output pulldown activates in the following conditions:

• When the device is disabled (VON/OFF < VON/OFF(LOW))

• If 1.0 V < VIN < VUVLO

Do not rely on the output pulldown circuit for discharging a large amount of output capacitance after the input

supply has collapsed because reverse current can flow from the output to the input. This reverse current flow

can cause damage to the device. See the Reverse Current section for more details.

7.3.6 Thermal Shutdown

The device contains a thermal shutdown protection circuit to disable the device when the junction temperature

(TJ) of the pass transistor rises to TSD(shutdown) (typical). Thermal shutdown hysteresis assures that the device

resets (turns on) when the temperature falls to TSD(reset) (typical).

The thermal time-constant of the semiconductor die is fairly short, thus the device can cycle on and off

when thermal shutdown is reached until power dissipation is reduced. Power dissipation during start up can

be high from large VIN – VOUT voltage drops across the device or from high inrush currents charging large

output capacitors. Under some conditions, the thermal shutdown protection disables the device before start up

completes.

For reliable operation, limit the junction temperature to the maximum listed in the Recommended Operating

Conditions table. Operation above this maximum temperature causes the device to exceed operational

specifications. Although the internal protection circuitry of the device is designed to protect against thermal

overall conditions, this circuitry is not intended to replace proper heat sinking. Continuously running the device

into thermal shutdown or above the maximum recommended junction temperature reduces long-term reliability.

7.4 Device Functional Modes

7.4.1 Device Functional Mode Comparison

Table 7-1 shows the conditions that lead to the different modes of operation. See the Electrical Characteristics

table for parameter values.

Table 7-1. 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)

7.4.2 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

LP2985

SLVS522Q – JULY 2004 – REVISED DECEMBER 2022

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