TPS73233DBVR datasheet(11/26 Pages) TI

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APPLICATION INFORMATION

INPUT AND OUTPUT CAPACITOR

TPS732xx

GND

OUT

Optional input capacitor.

May improve source

impedance, noise, or PSRR.

Optional output capacitor.

May improve load transient,

noise, or PSRR.

Optional bypass

capacitor to reduce

output noise.

OUTPUT NOISE

+ 32mVRMS

) R2)

+ 32mVRMS

OUT

REF

(1)

TPS73201

GND

OUT

x1.204

+ R

)

Optionalinputcapacitor.

Mayimprovesource

impedance,noise,orPSRR.

Optionaloutputcapacitor.

Mayimproveloadtransient

noise,orPSRR.

Optionalcapacitor

reducesoutputnoise

andimproves

transientresponse.

N(mVRMS) + 27

mVRMS

OUT(V)

(2)

TPS732xx

SBVS037L – AUGUST 2003 – REVISED AUGUST 2007

in addition to the internal 8k

Ω resistor, presents the

The TPS732xx belongs to a family of new generation

same impedance to the error amp as the 27k

Ω

LDO regulators that use an NMOS pass transistor to

bandgap reference output. This impedance helps

achieve

ultra-low-dropout

performance,

reverse

compensate

for

leakages

into

the

error

amp

current blockage, and freedom from output capacitor

terminals.

constraints. These features, combined with low noise

and an enable input, make the TPS732xx ideal for

portable applications. This regulator family offers a

REQUIREMENTS

wide selection of fixed output voltage versions and an

adjustable output version. All versions have thermal

Although an input capacitor is not required for

and

over-current

protection,

including

foldback

stability, it is good analog design practice to connect

current limit.

a 0.1

µF to 1µF low ESR capacitor across the input

supply near the regulator. This counteracts reactive

Figure 31 shows the basic circuit connections for the

input sources and improves transient response, noise

fixed voltage models. Figure 32 gives the connections

rejection,

and

ripple

rejection.

higher-value

for the adjustable output version (TPS73201).

capacitor may be necessary if large, fast rise-time

load transients are anticipated or the device is

located several inches from the power source.

The TPS732xx does not require an output capacitor

for stability and has maximum phase margin with no

capacitor. It is designed to be stable for all available

types and values of capacitors. In applications where

VIN – VOUT < 0.5V and multiple low ESR capacitors

are in parallel, ringing may occur when the product of

COUT and total ESR drops below 50nΩF. Total ESR

includes all parasitic resistances, including capacitor

ESR and board, socket, and solder joint resistance.

In most applications, the sum of capacitor ESR and

Figure 31. Typical Application Circuit for

trace resistance will meet this requirement.

Fixed-Voltage Versions

A precision band-gap reference is used to generate

the internal reference voltage, VREF. This reference is

the dominant noise source within the TPS732xx and

it generates approximately 32VRMS (10Hz to 100kHz)

at the reference output (NR). The regulator control

loop gains up the reference noise with the same gain

as the reference voltage, so that the noise voltage of

the regulator is approximately given by:

Since the value of VREF is 1.2V, this relationship

reduces to:

Figure 32. Typical Application Circuit for

Adjustable-Voltage Version

R1 and R2 can be calculated for any output voltage

for the case of no CNR.

using the formula shown in Figure 32. Sample

resistor values for common output voltages are

shown in Figure 2.

For best accuracy, make the parallel combination of

R1 and R2 approximately euqal to 19kΩ. This 19kΩ,

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