0.1

F

m

1

F

m

1

F

m

V

CC

VSIM

VBAT

GND

TXS4555

TXS4555

www.ti.com

SBOS550A

– FEBRUARY 2011 – REVISED MARCH 2011

APPLICATION INFORMATION

The LDO

’s included on the TXS4555 achieve ultra-wide bandwidth and high loop gain, resulting in extremely

noise, enable, low ground pin current make it ideal for portable applications. The device offers sub-bandgap

output voltages, current limit and thermal protection, and is fully specified from

–40°C to 125°C.

Figure 9. Typical Application Circuit for TXS4555

INPUT AND OUTPUT CAPACITOR REQUIREMENTS

It is good analog design practice to connect a 1.0

µF low equivalent series resistance (ESR) capacitor across the

input supply (VBAT) near the regulator. Also, a 0.1

µF is required for the logic core supply (VDDIO).

This capacitor will counteract reactive input sources and improve transient response, noise rejection, and ripple

rejection. A higher-value capacitor may be necessary if large, fast rise-time load transients are anticipated or if

the device is located several inches from the power source. The LDO

’s are designed to be stable with standard

ceramic capacitors of values 1.0

µF or larger. X5R- and X7R-type capacitors are best because they have

minimal variation in value and ESR over temperature. Maximum ESR should be

< 1.0 Ω.

OUTPUT NOISE

In most LDO

’s, the bandgap is the dominant noise source. To improve ac performance such as PSRR, output

connection for the bypass capacitor should connect directly to the GND pin of the device.

INTERNAL CURRENT LIMIT

The TXS4555 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 a current limit state for extended periods of time.

The PMOS pass element in the TXS4555 has a built-in body diode that conducts current when the voltage at

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

anticipated, external limiting may be appropriate.

DROPOUT VOLTAGE

behaves like a resistor in dropout.

STARTUP

The TXS4555 uses a quick-start circuit which allows the combination of very low output noise and fast start-up

times.

Copyright

© 2011, Texas Instruments Incorporated

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Product Folder Link(s): TXS4555