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TPS746

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SBVS337A – APRIL 2018 – REVISED DECEMBER 2018

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Copyright © 2018, Texas Instruments Incorporated

Feature Description (continued)

The TPS746 internal protection circuitry protects against overload conditions but is not intended to be activated

in normal operation. Continuously running the TPS746 into thermal shutdown degrades device reliability.

7.4 Device Functional Modes

7.4.1 Device Functional Mode Comparison

The Device Functional Mode Comparison table shows the conditions that lead to the different modes of

operation. See the Electrical Characteristics table for parameter values.

Table 1. Device Functional Mode Comparison

OPERATING MODE

PARAMETER

VIN

VEN

IOUT

TJ

Normal operation

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

VEN > VEN(HI)

IOUT < IOUT(max)

TJ < TSD(shutdown)

Dropout operation

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

VEN > VEN(HI)

IOUT < IOUT(max)

TJ < TSD(shutdown)

Disabled

(any true condition

disables the device)

VIN < VUVLO

VEN < VEN(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 enable voltage has previously exceeded the enable rising threshold voltage and has not yet decreased to

less than the enable falling threshold

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 startup), 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 enable pin to less than the maximum EN

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.