TPS73233DBVT datasheet(12/26 Pages) TI

12 / 26 page

www.ti.com

SHUTDOWN

N(mVRMS) + 8.5

mVRMS

OUT(V)

(3)

DROPOUT VOLTAGE

BOARD LAYOUT RECOMMENDATION TO

INTERNAL CURRENT LIMIT

TRANSIENT RESPONSE

TPS732xx

SBVS037L – AUGUST 2003 – REVISED AUGUST 2007

An internal 27k

Ω resistor in series with the noise

reduction pin (NR) forms a low-pass filter for the

The Enable pin is active high and is compatible with

voltage reference when an external noise reduction

standard TTL-CMOS levels. VEN below 0.5V (max)

capacitor, CNR, is connected from NR to ground. For

turns the regulator off and drops the ground pin

CNR = 10nF, the total noise in the 10Hz to 100kHz

current to approximately 10nA. When shutdown

bandwidth is reduced by a factor of ~3.2, giving the

capability is not required, the Enable pin can be

approximate relationship:

connected to VIN. When a pull-up resistor is used,

and operation down to 1.8V is required, use pull-up

resistor values below 50k

Ω. To ensure all charge is

removed from the gate of the pass element, the

Enable pin must be driven low before the input

for CNR = 10nF.

voltage is removed. If the Enable pin is not driven

This noise reduction effect is shown as RMS Noise

low, the pass element may be left on because of

Voltage vs CNR in the Typical Characteristics section.

stored charge on the gate.

The TPS73201 adjustable version does not have the

noise-reduction pin available. However, connecting a

feedback capacitor, CFB, from the output to the FB pin

The TPS732xx uses an NMOS pass transistor to

will reduce output noise and improve load transient

achieve extremely low dropout. When (VIN – VOUT) is

performance.

less than the dropout voltage (VDO), the NMOS pass

device is in its linear region of operation and the

The TPS732xx uses an internal charge pump to

input-to-output resistance is the RDS-ON of the NMOS

develop an internal supply voltage sufficient to drive

pass element.

the gate of the NMOS pass element above VOUT. The

charge pump generates ~250

µV of switching noise at

For large step changes in load current, the TPS732xx

~4MHz; however, charge-pump noise contribution is

requires a larger voltage drop from VIN to VOUT to

negligible at the output of the regulator for most

avoid degraded transient response. The boundary of

values of IOUT and COUT.

this transient dropout region is approximately twice

the dc dropout. Values of VIN – VOUT above this line

insure normal transient response.

IMPROVE PSRR AND NOISE PERFORMANCE

Operating in the transient dropout region can cause

To improve ac performance such as PSRR, output

an increase in recovery time. The time required to

noise, and transient response, it is recommended that

recover from a load transient is a function of the

the PCB be designed with separate ground planes for

magnitude of the change in load current rate, the rate

VIN and VOUT, with each ground plane connected only

change

load

current,

and

the

available

at the GND pin of the device. In addition, the ground

headroom

(VIN to VOUT voltage drop). Under

connection for the bypass capacitor should connect

worst-case conditions [full-scale instantaneous load

directly to the GND pin of the device.

change with (VIN – VOUT) close to dc dropout levels],

the TPS732xx can

take

couple

hundred

microseconds to return to the specified regulation

accuracy.

The TPS732xx internal current limit helps protect the

regulator during fault conditions. Foldback current

limit helps to protect the regulator from damage

during output short-circuit conditions by reducing

The low open-loop output impedance provided by the

current limit when VOUT drops below 0.5V. See

NMOS

pass

element

voltage

follower

Figure 12 in the Typical Characteristics section for a

configuration allows operation without an output

graph of IOUT vs VOUT.

capacitor

for

many

applications.

with

any

regulator, the addition of a capacitor (nominal value

µF) from the output pin to ground will reduce

undershoot magnitude but increase its duration. In

the adjustable version, the addition of a capacitor,

CFB, from the output to the adjust pin will also

improve the transient response.

Submit Documentation Feedback

Product Folder Link(s): TPS732xx

TPS73233DBVT Datasheet(PDF) 12 Page - Texas Instruments

TPS73233DBVT Datasheet(HTML) 12 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL