V =xV

N

OUT

10.5 V

m

RMS

V

TPS79901-Q1, TPS79912-Q1, TPS79915-Q1

TPS79918-Q1, TPS79925-Q1, TPS79927-Q1, TPS79933-Q1

SBVS097E

– MARCH 2008 – REVISED JANUARY 2012

www.ti.com

(1)

The TPS79901 adjustable version does not have the noise-reduction pin available, so ultra-low noise operation is

not possible. Noise can be minimized according to the previous recommendations.

Board Layout Recommendations to Improve PSRR and Noise Performance

To improve ac performance such as PSRR, output noise, and transient response, it is recommended that the

GND pin of the device. In addition, the ground connection for the bypass capacitor should connect directly to the

GND pin of the device.

Internal Current Limit

The TPS799xx internal current limit helps protect the regulator during fault conditions. During current limit, the

output sources a fixed amount of current that is largely independent of output voltage. For reliable operation, the

device should not be operated in current limit for extended periods of time.

The PMOS pass element in the TPS799xx has a built-in body diode that conducts current when the voltage at

OUT exceeds the voltage at IN. This current is not limited, so if extended reverse voltage operation is

anticipated, external limiting may be appropriate.

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.

Dropout Voltage

approximately with output current.

This effect is shown in Figure 9 through Figure 11 in the Typical Characteristics section.

Startup

Fixed voltage versions of the TPS799xx use a quick-start circuit to fast-charge the noise reduction capacitor,

ceramic capacitors are appropriate in this configuration.

startup is somewhat slower. The quick-start switch is closed for approximately 135

charged during the quick-start time, a 0.01

μF or smaller capacitor should be used.

Transient Response

As with any regulator, increasing the size of the output capacitor reduces over/undershoot magnitude but

improves stability and transient response. The transient response of the TPS799xx is enhanced by an active

pulldown that engages when the output overshoots by approximately 5% or more when the device is enabled.

When enabled, the pulldown device behaves like a 350-

Ω resistor to ground.

Undervoltage Lockout (UVLO)

The TPS799xx utilizes a UVLO circuit to keep the output shut off until internal circuitry is operating properly. The

UVLO circuit has a deglitch feature so that it typically ignores undershoot transients on the input if they are less

than 50-

μs duration.

8

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Product Folder Link(s): TPS79901-Q1 TPS79912-Q1 TPS79915-Q1 TPS79918-Q1 TPS79925-Q1 TPS79927-Q1

TPS79933-Q1