TPS799 datasheet(12/49 Pages) TI2

12 / 49 page

7.3 Feature Description

7.3.1 Internal Current Limit

The TPS799 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 TPS799 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 TPS799 uses a start-up circuit to quickly charge the noise reduction capacitor, CNR, if present (see the

Functional Block Diagrams). 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 CNR capacitor must be used; most ceramic capacitors are

appropriate for this configuration.

For fastest start-up, apply VIN 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 CNR is fully charged

during start-up, use a 0.01-μF or smaller capacitor.

7.3.4 Undervoltage Lockout (UVLO)

The TPS799 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.

TPS799

SBVS056L – JANUARY 2005 – REVISED FEBRUARY 2022

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TPS799 データシート(PDF) 12 Page - Texas Instruments