EN

IN

OUT

GND

0.1 PF

1 PF

VOUT

TPS791

BYPASS

0.1 PF

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16

TPS791

SLVS325D – MARCH 2001 – REVISED FEBRUARY 2018

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Copyright © 2001–2018, Texas Instruments Incorporated

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The TPS791 low-dropout (LDO) regulator is optimized for use in noise-sensitive battery-operated equipment. The

device features extremely low dropout voltages, high PSRR, ultralow output noise, low quiescent current (170 µA

typically), and an active-low, enable input to reduce supply currents to less than 1 µA when the regulator is

turned off.

8.1.1 External Capacitor Requirements

A 0.1-µF or larger ceramic input bypass capacitor, connected between IN and GND and located close to the

TPS791, is required for stability and to improve transient response, noise rejection, and ripple rejection. A higher-

value electrolytic input capacitor may be necessary if large, fast-rise-time load transients are anticipated and the

device is located several inches from the power source.

Like all low dropout regulators, the TPS791 requires an output capacitor connected between OUT and GND to

stabilize the internal control loop. The minimum recommended capacitance is 1 µF. Any 1-µF or larger ceramic

capacitor is suitable. The device is also stable with a 0.47-µF ceramic capacitor with at least 75 m

Ω of ESR.

The internal voltage reference is a key source of noise in an LDO regulator. The TPS791 has a BYPASS pin that

is connected to the voltage reference through a 250-k

Ω internal resistor. The 250-kΩ internal resistor, in

conjunction with an external bypass capacitor connected to the BYPASS pin, creates a low-pass filter to reduce

the voltage reference noise and, therefore, the noise at the regulator output. In order for the regulator to operate

properly, the current flow out of the BYPASS pin must be at a minimum because any leakage current creates an

IR drop across the internal resistor thus creating an output error. Therefore, the bypass capacitor must have

minimal leakage current.

For example, the TPS79118 exhibits approximately 15 µVRMS of output voltage noise using a 0.1-µF ceramic

bypass capacitor and a 1-µF ceramic output capacitor. The output starts up slower as the bypass capacitance

increases because of the RC time constant at the bypass pin that is created by the internal 250-k

Ω resistor and

external capacitor.

8.2 Typical Application

Figure 35 shows a typical application circuit.

Figure 35. Typical Application Circuit