0.1

µF

BYPASS

OUT

1

3

IN

EN

GND

2

4

5

2.2

µF

+

TPS793xx

0.01

µF

TPS79301-Q1, TPS79318-Q1, TPS79325-Q1

TPS79328-Q1, TPS793285-Q1, TPS79330-Q1

TPS79333-Q1, TPS793475-Q1

SGLS162H – APRIL 2003 – REVISED JANUARY 2013

www.ti.com

APPLICATION INFORMATION

The TPS793xx family of low-dropout (LDO) regulators has been 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 enable-input to reduce supply currents to less than 1 μA when the

regulator is turned off.

A typical application circuit is shown in Figure 22.

Figure 22. Typical Application Circuit

External Capacitor Requirements

A 0.1-

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

TPS793xx, is required for stability and improves 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 LDOs, the TPS793xx requires an output capacitor connected between OUT and GND to stabilize the

internal control loop. The minimum recommended capacitance is 2.2-

μF. Any 2.2-μF or larger ceramic capacitor

is suitable, provided the capacitance does not vary significantly over temperature.

The internal voltage reference is a key source of noise in an LDO regulator. The TPS793xx 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 TPS79328 exhibits only 32

capacitor and a 2.2-

μF ceramic output capacitor. Note that the output starts up slower as the bypass capacitance

increases due to the RC time constant at the BYPASS pin that is created by the internal 250-k

Ω resistor and

external capacitor.

Board Layout Recommendation to Improve PSRR and Noise Performance

To improve ac measurements like PSRR, output noise, and transient response, it is recommended that the board

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

pin of the device.

10

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Product Folder Links: TPS79301-Q1 TPS79318-Q1 TPS79325-Q1 TPS79328-Q1 TPS793285-Q1 TPS79330-Q1

TPS79333-Q1