TPS79301Q1,'79318Q1, '79325Q1

'79328Q1,'793285Q1,'79330Q1

TPS79333Q1,'793475Q1

SGLS162D − APRIL 2003 − REVISED SEPTEMBER 2007

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10

APPLICATION INFORMATION

The TPS793xx family of low-dropout (LDO) regulators has been optimized for use in noise-sensitive battery-operated

equipment. The device features low dropout voltages, high PSRR, ultralow output noise, low quiescent current (170

µA

typical), 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.

0.1

µF

BYPASS

OUT

1

3

IN

EN

GND

2

4

5

VI

VO

2.2

µF

+

TPS793xx

0.01

µF

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 low dropout regulators, 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

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 BYPASS 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 such as PSRR, output noise, and transient response, it is recommended that the board be

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