TPS799L54 Datasheet, PDF (10/22 Pages) Texas Instruments – 200-mA, Low-Dropout Linear Regulator with Built-In Inrush Current Protection

TPS799L54, TPS799L57
SBVS191B – APRIL 2012 – REVISED AUGUST 2014
www.ti.com
7.3 Feature Description
7.3.1 Internal Current Limit
The TPS799Lxx internal current limit helps protect the regulator during fault conditions. In current limit mode, the
output sources a fixed amount of current that is largely independent of the output voltage. For reliable operation,
do not operate the device in a current-limit state for extended periods of time.
The PMOS pass element in the TPS799Lxx has a built-in body diode that conducts current when the voltage at
OUT exceeds the voltage at IN. This current is not limited; therefore, if extended reverse voltage operation is
anticipated, external limiting may be required.
7.3.2 Shutdown
The enable pin (EN) is active high and is compatible with standard and low-voltage TTL-CMOS levels. When
shutdown capability is not required, EN can be connected to IN.
7.3.3 Start Up
The TPS799Lxx uses a start-up circuit to quickly charge the noise reduction capacitor, C_NR, if present (see the
Functional Block Diagram). This circuit allows for the combination of very low output noise and fast start-up
times. The NR pin is high impedance so a low leakage C_NR capacitor must be used; most ceramic capacitors are
appropriate for this configuration.
Note that for fastest start-up, apply V_IN first, and then drive the enable pin (EN) high. If EN is tied to IN, start-up is
somewhat slower. The start-up switch is closed for approximately 135 μs. To ensure that C_NR is fully charged
during start-up, use a 0.01-μF or smaller capacitor.
7.3.4 Undervoltage Lockout (UVLO)
The TPS799Lxx uses an undervoltage lockout circuit to keep the output shut off until internal circuitry is operating
properly. The UVLO circuit has a deglitch feature so that undershoot transients are typically ignored on the input
if these transients are less than 50 μs in duration.
7.4 Device Functional Modes
Driving EN over 1.2 V turns on the regulator. Driving EN below 0.4 V puts the regulator into shutdown mode,
thus reducing the operating current to 150 nA, nominal.
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