Datasheet LMX2978 Datasheet (National Semiconductor)

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LP2978
Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout
Regulator

Designed for Use with Very Low ESR Output Capacitors

LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator

March 2005

General Description

The LP2978 is a 50 mA, fixed-output voltage regulator de­signed to provide ultra low-dropout and low noise in battery
powered applications.

™

Using an optimized VIP
cess, the LP2978 delivers unequalled performance in all
specifications critical to battery-powered designs:

Dropout Voltage: Typically 120 mV

@

1 mA load.

Ground Pin Current: Typically 350 µA

@

75 µA
Enhanced Stability: The LP2978 is stable with output ca-

pacitor ESR as low as 5 mΩ, which allows the use of ceramic
capacitors on the output.

Sleep Mode: Less than 1 µA quiescent current when ON/
OFF pin is pulled low.

Smallest Possible Size: SOT-23 package uses absolute
minimum board space.

Precision Output: 1% tolerance output voltages available
(A grade).

Low Noise: By adding a 10 nF bypass capacitor, output
noise can be reduced to 30 µV (typical).

1 mA load.

(Vertically Integrated PNP) pro-

@

50 mA load, and 7 mV

@

50 mA load, and

Block Diagram

Features

n Ultra low dropout voltage
n Smallest possible size (SOT-23 Package)
n Requires minimum external components
n Stable with low-ESR output capacitor

<

n

1 µA quiescent current when shut down

n Low ground pin current at all loads
n Output voltage accuracy 1% (A Grade)
n High peak current capability
n Wide supply voltage range (16V max)
n Low Z
n Overtemperature/overcurrent protection
n −40˚C to +125˚C junction temperature range
n Custom voltages available

: 0.3Ω typical (10 Hz to 1 MHz)

OUT

Applications

n Cellular Phone
n Palmtop/Laptop Computer
n Personal Digital Assistant (PDA)
n Camcorder, Personal Stereo, Camera

10093501

VIP™is a trademark of National Semiconductor Corporation.

© 2005 National Semiconductor Corporation DS100935 www.national.com

Basic Application Circuit

LP2978

*ON/OFF input must be actively terminated. Tie to VINif this function is not to be used.

**Minimum capacitance is shown to ensure stability (may be increased without limit). Ceramic capacitor required for output (see Application Hints).

***Reduces output noise (may be omitted if application is not noise critical). Use ceramic or film type with very low leakage current (see Application Hints).

10093502

Connection Diagram

See NS Package Number MF05A

10093503

Ordering Information

TABLE 1. Package Marking and Ordering Information

Output Voltage (V) Grade Order Information Package Marking Supplied As:

3.8 A LP2978AIM5X-3.8 LØLA 3000 Units on Tape and Reel

3.8 A LP2978AIM5-3.8 LØLA 1000 Units on Tape and Reel

3.8 STD LP2978IM5X-3.8 LØLB 3000 Units on Tape and Reel

3.8 STD LP2978IM5-3.8 LØLB 1000 Units on Tape and Reel

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LP2978

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Storage Temperature Range −65˚C to +150˚C

Operating Junction Temperature
Range −40˚C to +125˚C

Lead Temp. (Soldering, 5 sec.) 260˚C

Input Supply Voltage (Survival) −0.3V to +16V

Input Supply Voltage (Operating) 2.5V to +16V

Shutdown Input Voltage (Survival) −0.3V to +16V

Output Voltage (Survival, (Note 4)) −0.3V to +9V

I

(Survival) Short Circuit

OUT

Protected

Input-Output Voltage (Survival, −0.3V to +16V

(Note 5))

ESD Rating (Note 2) 2 kV

Power Dissipation (Note 3) Internally Limited

Electrical Characteristics

Limits in standard typeface are for TJ= 25˚C. and limits in boldface type apply over the full operating temperature range. Un­less otherwise specified: V

(NOM) + 1V, IL= 1 mA, CIN= 1 µF, C

IN=VO

Symbol Parameter Conditions Typ

∆V

O

Output Voltage
Tolerance

IL= 1 mA −1.0 1.0 −1.5 1.5

1mA≤ IL≤ 50 mA −1.5 1.5 −2.5 2.5

Output Voltage VO(NOM)+1V ≤ VIN≤ 16V 0.007 0.014 0.014

Line Regulation 0.032 0.032

V

IN–VO

Dropout Voltage

IL=0 1 3 3

(Note 7)

I

= 1 mA 7 10 10

L

I

=10mA 40 60 60

L

I

= 50 mA 120 150 150

L

I

GND

V

ON/OFF

I

ON/OFF

e

n

(SC) Short Circuit Current RL= 0 (Steady State) 400 mA

I

O

I

(PK) Peak Output Current V

O

Ground Pin Current IL= 0 65 95 95

I

= 1 mA 75 110 110

L

I

= 10 mA 120 220 220

L

I

= 50 mA 350 600 600

L

<

ON/OFF

ON/OFF

ON/OFF

ON/OFF

0.3V 0.01 0.8 0.8

<

0.15V 0.05 2 2

= 0 0.01 −2 −2

=5V 5 15 15

ON/OFF Input Voltage
(Note 8)

ON/OFF Input Current V

V

V

High = O/P ON 1.4 1.6 1.6

Low = O/P OFF 0.55 0.15 0.15

V

Output Noise BW = 300 Hz to 50 kHz,

Voltage (RMS) C

Ripple Rejection f = 1 kHz, C

=10µF 30 µV

OUT

C

C

=10nF

BYPASS

=10nF

BYPASS

=10µF

OUT

≥ Vo(NOM) −5% 350 mA

OUT

= 4.7 µF, V

OUT

ON/OFF

= 2V.

LP2978AI-X.X LP2978I-X.X

Min Max Min Max

−2.5 2.5 −3.5 3.5

55

15 15

90 90

225 225

125 125

170 170

400 400

1000 1000

45 dB

Units(Note 6) (Note 6)

%V

NOM

%/V

mV

µA

V

µA

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Electrical Characteristics (Continued)

Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the

LP2978

device outside of its rated operating conditions.

Note 2: The ESD rating of pins 3 and 4 is 1 kV.

Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, T

and the ambient temperature, T

. The maximum allowable power dissipation at any ambient temperture is calculated using:

A

(MAX), the junction-to-ambient thermal resistance, θ

J

J-A

,

Where the value of θ
temperature, and the regulator will go into thermal shutdown.

Note 4: If used in a dual-supply system where the regulator load is returned to a negative supply, the LP2978 output must be diode-clamped to ground.

Note 5: The output PNP structure contains a diode between the V

turn on this diode.

Note 6: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL).

Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential.

Note 8: The ON/OFF input must be properly driven to prevent possible misoperation. For details, refer to Application Hints.

for the SOT-23 package is 220˚C/W in a typical PC board mounting. Exceeding the maximum allowable dissipation will cause excessive die

J-A

to V

IN

terminals that is normally reverse-biased. Reversing the polarity from VINto V

OUT

OUT

will

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Application Hints

EXTERNAL CAPACITORS

Like any low-dropout regulator, the LP2978 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.

Input Capacitor

An input capacitor whose capacitance is ≥ 1 µF is required
between the LP2978 input and ground (the amount of ca­pacitance may be increased without limit).

This capacitor must be located a distance of not more than 1
cm from the input pin and returned to a clean analog ground.
Any good quality ceramic, tantalum, or film capacitor may be
used at the input.

Important: Tantalum capacitors can suffer catastrophic fail­ure due to surge current when connected to a low­impedance source of power (like a battery or very large
capacitor). If a Tantalum capacitor is used at the input, it
must be guaranteed by the manufacturer to have a surge
current rating sufficient for the application.

There are no requirements for ESR on the input capacitor,
but tolerance and temperature coefficient must be consid­ered when selecting the capacitor to ensure the capacitance
will be ≥ 1 µF over the entire operating temperature range.

Output Capacitor

The LP2978 is designed specifically to work with ceramic
output capacitors, utilizing circuitry which allows the regula­tor to be stable across the entire range of output current with
an output capacitor whose ESR is as low as 5 mΩ.Itmay
also be possible to use Tantalum or film capacitors at the
output, but these are not as attractive for reasons of size and
cost (see next section Capacitor Characteristics).

The output capacitor must meet the requirement for mini­mum amount of capacitance and also have an ESR (equiva­lent series resistance) value which is within the stable range.
Curves are provided which show the stable ESR range as a
function of load current (see ESR graph below).

ceramic capacitors can exhibit large changes in capacitance
with temperature (see next section, Capacitor Characteris-
tics).

The output capacitor must be located not more than 1 cm
from the output pin and returned to a clean analog ground.

Noise Bypass Capacitor

Connecting a 10 nF capacitor to the Bypass pin significantly
reduces noise on the regulator output. It should be noted that
the capacitor is connected directly to a high-impedance cir­cuit in the bandgap reference.

Because this circuit has only a few microamperes flowing in
it, any significant loading on this node will cause a change in
the regulated output voltage. For this reason, DC leakage
current through the noise bypass capacitor must never ex­ceed 100 nA, and should be kept as low as possible for best
output voltage accuracy.

The types of capacitors best suited for the noise bypass
capacitor are ceramic and film. High-quality ceramic capaci­tors with either NPO or COG dielectric typically have very
low leakage. 10 nF polypropolene and polycarbonate film
capacitors are available in small surface-mount packages
and typically have extremely low leakage current.

CAPACITOR CHARACTERISTICS

The LP2978 was designed to work with ceramic capacitors
on the output to take advantage of the benefits they offer: for
capacitance values in the 2.2 µF to 4.7 µF range, ceramics
are the least expensive and also have the lowest ESR
values (which makes them best for eliminating high­frequency noise). The ESR of a typical 2.2 µF ceramic
capacitor is in the range of 10 mΩ to 20 mΩ, which easily
meets the ESR limits required for stability by the LP2978.

One disadvantage of ceramic capacitors is that their capaci­tance can vary with temperature. Most large value ceramic
capacitors (≥ 2.2 µF) are manufactured with the Z5U or Y5V
temperature characteristic, which results in the capacitance
dropping by more than 50% as the temperature goes from
25˚C to 85˚C.

This could cause problems if a 2.2 µF capacitor were used
on the output since it will drop down to approximately 1 µF at
high ambient temperatures (which could cause the LP2978
to oscillate). If Z5U or Y5V capacitors are used on the output,
a minimum capacitance value of 4.7 µF must be observed.

A better choice for temperature coefficient in ceramic capaci­tors is X7R, which holds the capacitance within
fortunately, the larger values of capacitance are not offered
by all manufacturers in the X7R dielectric.

±

15%. Un-

LP2978

10093507

Important: The output capacitor must maintain its ESR
within the stable region over the full operating temperature
range of the application to assure stability.

The LP2978 requires a minimum of 2.2 µF on the output
(output capacitor size can be increased without limit).

It is important to remember that capacitor tolerance and
variation with temperature must be taken into consideration
when selecting an output capacitor so that the minimum
required amount of output capacitance is provided over the
full operating temperature range. It should be noted that

TANTALUM

Tantalum capacitors are less desirable than ceramics for use
as output capacitors because they are more expensive when
comparing equivalent capacitance and voltage ratings in the
1 µF to 4.7 µF range.

Another important consideration is that Tantalum capacitors
have higher ESR values than equivalent size ceramics. This
means that while it may be possible to find a Tantalum
capacitor with an ESR value within the stable range, it would
have to be larger in capacitance (which means bigger and
more costly) than a ceramic capacitor with the same ESR
value.

It should also be noted that the ESR of a typical Tantalum will
increase about 2:1 as the temperature goes from 25˚C down
to −40˚C, so some guard band must be allowed.

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Application Hints (Continued)

LP2978

ON/OFF INPUT OPERATION

The LP2978 is shut off by driving the ON/OFF input low, and
turned on by pulling it high. If this feature is not to be used,
the ON/OFF input should be tied to V
output on at all times.

To assure proper operation, the signal source used to drive
the ON/OFF input must be able to swing above and below
the specified turn-on/turn-off voltage thresholds listed in the
Electrical Characteristics section under V
mis-operation, the turn-on (and turn-off) voltage signals ap­plied to the ON/OFF input must have a slew rate which is
≥ 40 mV/µs.

Caution: the regulator output voltage can not be guaranteed
if a slow-moving AC (or DC) signal is applied that is in the
range between the specified turn-on and turn-off voltages
listed under the electrical specification V
cal Characteristics).

to keep the regulator

IN

ON/OFF

ON/OFF

. To prevent

(see Electri-

REVERSE INPUT-OUTPUT VOLTAGE

The PNP power transistor used as the pass element in the
LP2978 has an inherent diode connected between the regu­lator output and input. During normal operation (where the
input voltage is higher than the output) this diode is reverse­biased.

However, if the output is pulled above the input, this diode
will turn ON and current will flow into the regulator output. In
such cases, a parasitic SCR can latch which will allow a high
current to flow into V

(and out the ground pin), which can

IN

damage the part.
In any application where the output may be pulled above the

input, an external Schottky diode must be connected from

to V

V

IN

(cathode on VIN, anode on V

OUT

), to limit the

OUT

reverse voltage across the LP2978 to 0.3V (see Absolute
Maximum Ratings).

www.national.com 6

Physical Dimensions inches (millimeters) unless otherwise noted

LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator

5-Lead Small Outline Package (M5)

NS Package Number MF05A

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.

For the most current product information visit us at www.national.com.

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