TPS7A39
ZHCSGP0A –JULY 2017–REVISED SEPTEMBER 2017
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7.4 Device Functional Modes
7.4.1 Normal Operation
The device regulates to the nominal output voltage under the following conditions:
•
•
•
The input voltage is at least as high as |VINx(min)
The input voltage is greater than the nominal output voltage added to the dropout voltage
The enable voltage has previously exceeded the enable rising threshold voltage and has not decreased
below the enable falling threshold
|
•
•
The output current is less than the current limit
The device junction temperature is less than TSD
7.4.2 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 of operation, the
output voltage is the same as the input voltage minus the dropout voltage. The transient performance of the
device is significantly degraded because the pass device (as a bipolar junction transistor, or BJT) is in saturation
and no longer controls the current through the LDO. Line or load transients in dropout can result in large output
voltage deviations.
7.4.3 Disabled
The device is disabled under the following conditions:
•
The enable voltage is less than the enable falling threshold voltage or has not yet exceeded the enable rising
threshold
•
The device junction temperature is greater than the thermal shutdown temperature
表 3 shows the conditions that lead to the different modes of operation.
表 3. Device Functional Mode Comparison
PARAMETER
OPERATING MODE
VIN
VEN
IOUT
TJ
|VINx| > |VOUT(nom)| + |VDOx| and
Normal mode
Dropout mode
VEN > VIH
|IOUTx| < |ILIMx
|
T J < 125°C
|VINx| > |VINx(min)
|
|VINx(min)| < |VINx| < |VOUTx(nom)| +
VEN > VIH
VEN < VIL
—
—
TJ < 125°C
TJ > TSD
|VDOx
|
Disabled mode
(any true condition disables the device)
—
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