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TLV751 データシート(PDF) 17 Page - Texas Instruments

部品番号. TLV751
部品情報  TLV751 Dual, 500-mA, High-Accuracy, LDO in a Small-Size Package
ダウンロード  31 Pages
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メーカー  TI1 [Texas Instruments]
ホームページ  http://www.ti.com
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TLV751 Datasheet(HTML) 17 Page - Texas Instruments

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Input Voltage
Output Voltage
Output Voltage in
normal regulation.
Dropout
VOUT = VIN - VDO
VIN = VOUT(nom) + VDO
Response time for
LDO to get back into
regulation.
Load current discharges
output voltage.
Time
17
TLV751
www.ti.com
SBVS385B – DECEMBER 2019 – REVISED APRIL 2020
Product Folder Links: TLV751
Submit Documentation Feedback
Copyright © 2019–2020, Texas Instruments Incorporated
Application Information (continued)
8.1.3 Dropout Voltage
The TLV751 uses a PMOS pass transistor to achieve low dropout. When (VIN – VOUT) is less than the dropout
voltage (VDO), the PMOS pass device is in the linear region of operation and the input-to-output resistance is the
RDS(ON) of the PMOS pass element. VDO scales approximately with output current because the PMOS device
behaves like a resistor in dropout mode. As with any linear regulator, PSRR and transient response degrade as
(VIN – VOUT) approaches dropout operation.
8.1.4 Exiting Dropout
Some applications have transients that place the LDO into dropout, such as slower ramps on VIN during start-up.
As with other LDOs, the output may overshoot on recovery from these conditions. A ramping input supply causes
an LDO to overshoot on start-up, as shown in Figure 39, when the slew rate and voltage levels are in the correct
range. Use an enable signal to avoid this condition.
Figure 39. Startup Into Dropout
Line transients out of dropout can also cause overshoot on the output of the regulator. These overshoots are
caused by the error amplifier having to drive the gate capacitance of the pass element and bring the gate back to
the correct voltage for proper regulation. Figure 40 illustrates what is happening internally with the gate voltage
and how overshoot can be caused during operation. When the LDO is placed in dropout, the gate voltage (VGS)
is pulled all the way down to ground to give the pass device the lowest on-resistance as possible. However, if a
line transient occurs when the device is in dropout, the loop is not in regulation and can cause the output to
overshoot until the loop responds and the output current pulls the output voltage back down into regulation. If
these transients are not acceptable, then continue to add input capacitance in the system until the transient is
slow enough to reduce the overshoot.


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