LP2954/LP2954A
5V and Adjustable Micropower Low-Dropout Voltage
Regulators

General Description

The LP2954 is a 5V micropower voltage regulator with very
low quiescent current (90 µA typical at 1 mA load) and very
low dropout voltage (typically 60 mV at light loads and
470 mV at 250 mA load current).

The quiescent current increases only slightly at dropout
(120 µA typical), which prolongs battery life.

The LP2954 with a fixed 5V output is available in the
three-lead TO-220 and TO-263 packages. The adjustable
LP2954 is provided in an 8-lead surface mount, small outline
package. The adjustable version also provides a resistor net-
work which can be pin strapped to set the output to 5V.

Reverse battery protection is provided.

The tight line and load regulation (0.04% typical), as well as
very low output temperature coefficient make the LP2954
well suited for use as a low-power voltage reference.

Output accuracy is guaranteed at both room temperature
and over the entire operating temperature range.

Features

5V output within 1.2% over temperature (A grade)

Adjustable 1.23 to 29V output voltage available
(LP2954IM and LP2954AIM)

Guaranteed 250 mA output current

Extremely low quiescent current

Low dropout voltage

Reverse battery protection

Extremely tight line and load regulation

Very low temperature coefficient

Current and thermal limiting

Pin compatible with LM2940 and LM340 (5V version
only)

Adjustable version adds error flag to warn of output drop
and a logic-controlled shutdown

Applications

High-efficiency linear regulator

Low dropout battery-powered regulator

Package Outline and Ordering Information

TO-220 3Lead Plastic Package

DS011128-2

Front View

Order Number LP2954AIT or LP2954IT

See NS Package T03B

SO-8 Small Outline Surface Mount

DS011128-33

Top View

Order Number LP2954AIM or LP2954IM

See NS Package M08A

June 1999

LP2954/LP2954A

and

Adjustable

Micropower

Low-Dropout

oltage

Regulators

DS011128

www.national.com

Absolute Maximum Ratings

(Note 1)

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

Operating Junction Temperature

Range

LP2954AI/LP2954I

-40°C to +125°C

Storage Temperature Range

-65°C to +150°C

Lead Temperature

(Soldering, 5 seconds)

260°C

Power Dissipation (Note 2)

Internally Limited

Input Supply Voltage

-20V to +30V

ESD Rating

2 kV

Electrical Characteristics

Limits in standard typeface are for T

= 25°C, bold typeface applies over the -40°C to +125°C temperature range. Limits

are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Un-
less otherwise noted: V

= 6V, I

= 1 mA, C

= 2.2 µF.

Symbol

Parameter

Conditions

Typical

2954AI

2954I

Units

Min

Max

Min

Max

Output Voltage

5.0

4.975

5.025

4.950

5.050

4.940

5.060

4.900

5.100

1 mA

250 mA

5.0

4.930

5.070

4.880

5.120

Output Voltage

(Note 3)

100

150

ppm/°C

Temp. Coefficient

Line Regulation

= 6V to 30V

0.03

0.10

0.20

0.20

0.40

Load Regulation

= 1 to 250 mA

0.16

0.20

= 0.1 to 1 mA

0.04

0.20

0.30

(Note 4)

Dropout Voltage

= 1 mA

100

(Note 5)

150

= 50 mA

240

300

420

= 100 mA

310

400

520

= 250 mA

470

600

800

GND

Ground Pin Current

= 1 mA

150

µA

(Note 6)

180

= 50 mA

1.1

2.5

= 100 mA

4.5

= 250 mA

GND

Ground Pin

= 4.5V

170

Current at Dropout

120

210

µA

(Note 6)

LIMIT

Current Limit

OUT

= 0V

380

500

530

Thermal Regulation

(Note 7)

0.05

0.2

%/W

Output Noise

= 2.2 µF

400

µV RMS

Voltage

(10 Hz to 100 kHz)

= 33 µF

260

= 100 mA

=33µF(Note 9)

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Electrical Characteristics

(Continued)

Limits in standard typeface are for T

= 25°C, bold typeface applies over the -40°C to +125°C temperature range. Limits

are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Un-
less otherwise noted: V

= 6V, I

= 1 mA, C

= 2.2 µF.

Symbol

Parameter

Conditions

Typical

2954AI

2954I

Units

Min

Max

Min

Max

Additional Specifications for the Adjustable Device (LP2954AIM and LP2954IM)

REF

Reference Voltage

(Note 10)

1.230

1.215
1.205

1.245
1.255

1.205
1.190

1.255
1.270

REF

Reference Voltage
Line Regulation

=2.5V to

VO(NOM)+1V

0.03

0.1

0.2

=2.5V to

VO(NOM)+1V to 30V
(Note 11)

0.2

0.4

REF

Reference Voltage
Temperature
Coefficient

(Note 3)

ppm/°C

(FB)

Feedback Pin Bias
Current

40
60

GND

Ground Pin Current
at Shutdown (Note
6)

SHUTDOWN

1.1V

105

140

µA

(SINK)

Output

OFF

Pulldown Current

(Note 12)

30
20

Dropout Detection Comparator

Output

HIGH

Leakage Current

=30V

0.01

1
2

µA

Output

LOW

Voltage

(NOM)-0.5V

(COMP)=400µA

150

250
400

THR

(MAX)

Upper Threshold
Voltage

(Note 13)

-60

-80
-95

-35
-25

-80
-95

-35
-25

THR

(MIN)

Lower Threshold
Voltage

(Note 13)

-85

-110
-160

-55
-40

-110
-160

-55
-40

HYST

Hysteresis

(Note 13)

Shutdown Input

Input Offset Voltage

(Referred to V

REF

)

-7.5

-10

7.5

-7.5

-10

7.5

HYST

Hysteresis

Input Bias Current

(S/D)=0V to 5V

-30
-50

30
50

-30
-50

30
50

Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the de-
vice outside of its rated operating conditions.

Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, T

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

J-A

and the ambient temperature, T

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

Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. The junction-to-ambient
thermal resistance of the TO-220 (without heatsink) is 60°C/W, 73°C/W for the TO-263, and 160°C/W for the SO-8. If the TO-263 package is used, the thermal re-
sistance can be reduced by increasing the P.C. board copper area thermally connected to the package: Using 0.5 square inches of copper area,

is 50°C/W; with

1 square inch of copper area,

is 37°C/W; and with 1.6 or more square inches of copper area,

is 32°C/W. The junction-to-case thermal resistance is 3°C/W.

If an external heatsink is used, the effective junction-to-ambient thermal resistance is the sum of the junction-to-case resistance (3°C/W), the specified thermal re-
sistance of the heatsink selected, and the thermal resistance of the interface between the heatsink and the LP2954. Some typical values are listed for interface ma-
terials used with TO-220:

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Electrical Characteristics

(Continued)

TABLE 1. Typical Values of Case-to-Heatsink

Thermal Resistance (°C/W) (Data from AAVID Eng.)

Silicone grease

1.0

Dry interface

1.3

Mica with grease

1.4

TABLE 2. Typical Values of Case-to-Heatsink

Thermal Resistance (°C/W) (Data from Thermalloy)

Thermasil III

1.3

Thermasil II

1.5

Thermalfilm (0.002) with grease

2.2

Note 3: Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.

Note 4: Regulation is measured at constant junction temperature using low duty cycle pulse testing. Parts are tested separately for load regulation in the load
ranges 0.1 mA1 mA and 1 mA250 mA. Changes in output voltage due to heating effects are covered by the thermal regulation specification.

Note 5: 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 6: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the load current plus the ground pin current.

Note 7: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation
effects. Specifications are for 200 mA load pulse at V

= 20V (3W pulse) for T = 10 ms.

Note 8: When used in dual-supply systems where the regulator load is returned to a negative supply, the output voltage must be diode-clamped to ground.

Note 9: Connect a 0.1µF capacitor from the output to the feedback pin.

Note 10: V

REF

OUT

-1V), 2.3V

30V, 100µA

250mA.

Note 11: Two seperate tests are performed, one covering V

=2.5V to V

(NOM)+1V and the other test for V

=2.5V to V

(NOM)+1V to 30V.

Note 12: V

SHUTDOWN

1.1V, VOUT=V

(NOM).

Note 13: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at
V

(NOM)+1V. To express these thresholds in terms of output voltage change, multiply by the Error amplifier gain, which is V

OUT

REF

=(R1+R2)/R2.

Note 14: Human body model, 200pF discharged through 1.5k

Typical Performance Characteristics

Quiescent Current

DS011128-12

Quiescent Current

DS011128-13

Ground Pin Current vs Load

DS011128-14

Ground Pin Current

DS011128-15

Ground Pin Current

DS011128-16

Output Noise Voltage

DS011128-17

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Typical Performance Characteristics

(Continued)

Application Hints

EXTERNAL CAPACITORS

A 2.2 µF (or greater) capacitor is required between the out-
put pin and the ground to assure stability (refer to

Figure 1).

Without this capacitor, the part may oscillate. Most types of
tantalum or aluminum electrolytics will work here. Film types
will work, but are more expensive. Many aluminum electro-
lytics contain electrolytes which freeze at -30°C, which re-
quires the use of solid tantalums below -25°C. The important
parameters of the capacitor are an ESR of about 5

or less

and a resonant frequency above 500 kHz (the ESR may in-
crease by a factor of 20 or 30 as the temperature is reduced
from 25°C to -30°C). The value of this capacitor may be in-
creased without limit. At lower values of output current, less
output capacitance is required for stability. The capacitor can
be reduced to 0.68 µF for currents below 10 mA or 0.22 µF
for currents below 1 mA.

A 1 µF capacitor should be placed from the input pin to
ground if there is more than 10 inches of wire between the in-
put and the AC filter capacitor or if a battery input is used.

Programming the output for voltages below 5V runs the error
amplifier at lower gains requiring more output capacitance
for stability. At 3.3V output, a minimum of 4.7 µF is required.
For the worst case condition of 1.23V output and 250 mA of
load current, a 6.8 µF (or larger) capacitor should be used.

Stray capacitance to the Feedback terminal can cause insta-
bility. This problem is most likely to appear when using high
value external resistors to set the output voltage. Adding a
100 pF capacitor between the Output and Feedback pins
and increasing the output capacitance to 6.8 µF (or greater)
will cure the problem.

MINIMUM LOAD

When setting the output voltage using an external resistive
divider, a minimum current of 1 µA is recommended through
the resistors to provide a minimum load.

It should be noted that a minimum load current is specified in
several of the electrical characteristic test conditions, so this
value must be used to obtain correlation on these tested lim-
its. The part is parametrically tested down to 100 µA, but is
functional with no load.

DROPOUT VOLTAGE

The dropout voltage of the regulator is defined as the mini-
mum input-to-output voltage differential required for the out-
put voltage to stay within 100 mV of the output voltage mea-
sured with a 1V differential. The dropout voltages for various
values of load current are listed under Electrical Characteris-
tics.

If the regulator is powered from a rectified AC source with a
capacitive filter, the minimum AC line voltage and maximum
load current must be used to calculate the minimum voltage
at the input of the regulator. The minimum input voltage, in-
cluding AC ripple on the filter capacitor , must not drop
below the voltage required to keep the LP2954 in regulation.
It is also advisable to verify operating at minimum operating
ambient temperature, since the increasing ESR of the filter
capacitor makes this a worst-case test for dropout voltage
due to increased ripple amplitude.

HEATSINK REQUIREMENTS

A heatsink may be required with the LP2954 depending on
the maximum power dissipation and maximum ambient tem-
perature of the application. Under all possible operating con-
ditions, the junction temperature must be within the range
specified under Absolute Maximum Ratings.

To determine if a heatsink is required, the maximum power
dissipated by the regulator, P(max), must be calculated. It is
important to remember that if the regulator is powered from
a transformer connected to the AC line, the maximum
specified AC input voltage must be used (since this pro-
duces the maximum DC input voltage to the regulator).

Fig-

ure 1 shows the voltages and currents which are present in
the circuit. The formula for calculating the power dissipated
in the regulator is also shown in

Figure 1.

Maximum Power Dissipation
(TO-263) (See (Note 2) )

DS011128-11

www.national.com

Application Hints

(Continued)

The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T

(max). This is calculated

by using the formula:

(max) = T

(max) - T

(max)

where: T

(max) is the maximum allowable junction

temperature

(max) is the maximum ambient temperature

Using the calculated values for T

(max) and P(max), the re-

quired value for junction-to-ambient thermal resistance,

(J-A)

, can now be found:

(J-A)

= T

(max)/P(max)

If the calculated value is 60° C/W or higher , the regulator
may be operated without an external heatsink. If the calcu-
lated value is below 60° C/W, an external heatsink is re-
quired. The required thermal resistance for this heatsink can
be calculated using the formula:

(H-A)

(J-A)

(J-C)

(C-H)

where:

(J-C)

is the junction-to-case thermal resistance, which is

specified as 3° C/W maximum for the LP2954.

(C-H)

is the case-to-heatsink thermal resistance, which is

dependent on the interfacing material (if used). For details
and typical values, refer to (Note 2) listed at the end of the
ELECTRICAL CHARACTERISTICS section.

(H-A)

is the heatsink-to-ambient thermal resistance. It is this

specification (listed on the heatsink manufacturers data
sheet) which defines the effectiveness of the heatsink. The
heatsink selected must have a thermal resistance which is
equal to or lower than the value of

(H-A)

calculated from the

above listed formula.

PROGRAMMING THE OUTPUT VOLTAGE

The regulator may be pin-strapped for 5V operation using its
internal resistive divider by tying the Output and Sense pins
together and also tying the Feedback and 5V Tap pins to-
gether.

Alternatively, it may be programmed for any voltage between
the 1.23V reference and the 30V maximum rating using an
external pair of resistors (see

Figure 2). The complete equa-

tion for the output voltage is:

where V

REF

is the 1.23V reference and I

is the Feedback

pin bias current (-20 nA typical). The minimum recom-
mended load current of 1 µA sets an upper limit of 1.2 M

the value of R2 in cases where the regulator must work with
no load (see MINIMUM LOAD ). I

will produce a typical 2%

error in V

OUT

which can be eliminated at room temperature

by trimming R1. For better accuracy, choosing R2 = 100 k

will reduce this error to 0.17% while increasing the resistor
program current to 12 µA. Since the typical quiescent current
is 120 µA, this added current is negligible.

DROPOUT DETECTION COMPARATOR

This comparator produces a logic "LOW" whenever the out-
put falls out of regulation by more than about 5%. This figure
results from the comparator's built-in offset of 60 mV divided
by the 1.23V reference (refer to block diagrams on page 1).
The 5% low trip level remains constant regardless of the pro-
grammed output voltage. An out-of-regulation condition can
result from low input voltage, current limiting, or thermal lim-
iting.

Figure 3 gives a timing diagram showing the relationship be-
tween the output voltage, the ERROR output, and input volt-
age as the input voltage is ramped up and down to a regula-
tor programmed for 5V output. The ERROR signal becomes
low at about 1.3V input. It goes high at about 5V input, where
the output equals 4.75V. Since the dropout voltage is load
dependent, the input voltage trip points will vary with load
current. The output voltage trip point does not vary.

The comparator has an open-collector output which requires
an external pull-up resistor. This resistor may be connected
to the regulator output or some other supply voltage. Using
the regulator output prevents an invalid "HIGH" on the com-
parator output which occurs if it is pulled up to an external
voltage while the regulator input voltage is reduced below
1.3V. In selecting a value for the pull-up resistor, note that
while the output can sink 400 µA, this current adds to battery
drain. Suggested values range from 100 k

to 1 M

. This

resistor is not required if the output is unused.

When V

1.3V, the error flag pin becomes a high imped-

ance, allowing the error flag voltage to rise to its pull-up volt-
age. Using V

OUT

as the pull-up voltage (rather than an exter-

nal 5V source) will keep the error flag voltage below 1.2V
(typical) in this condition. The user may wish to divide down
the error flag voltage using equal-value resistors (10 k

sug-

gested) to ensure a low-level logic signal during any fault
condition, while still allowing a valid high logic level during
normal operation.

DS011128-5

*See External Capacitors
P

Total

= (V

-5) I

+ (V

) I

FIGURE 1. Basic 5V Regulator Circuit

DS011128-36

See Application Hints

Drive with TTL-low to shut down

FIGURE 2. Adjustable Regulator

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Application Hints

(Continued)

OUTPUT ISOLATION

The regulator output can be left connected to an active volt-
age source (such as a battery) with the regulator input power
turned off, as long as the regulator ground pin is con-
nected to ground . If the ground pin is left floating, damage
to the regulator can occur if the output is pulled up by an
external voltage source.

REDUCING OUTPUT NOISE

In reference applications it may be advantageous to reduce
the AC noise present on the output. One method is to reduce
regulator bandwidth by increasing output capacitance. This
is relatively inefficient, since large increases in capacitance
are required to get significant improvement.

Noise can be reduced more effectively by a bypass capacitor
placed across R1 (refer to

Figure 2). The formula for select-

ing the capacitor to be used is:

This gives a value of about 0.1 µF. When this is used, the
output capacitor must be 6.8 µF (or greater) to maintain sta-
bility. The 0.1 µF capacitor reduces the high frequency gain
of the circuit to unity, lowering the output noise from 260 µV
to 80 µV using a 10 Hz to 100 kHz bandwidth. Also, noise is
no longer proportional to the output voltage, so improve-
ments are more pronounced at high output voltages.

SHUTDOWN INPUT

A logic-level signal will shut off the regulator output when a
"LOW" (

1.2V) is applied to the Shutdown input.

To prevent possible mis-operation, the Shutdown input must
be

actively

terminated.

the

input

driven

from

open-collector logic, a pull-up resistor (20 k

to 100 k

rec-

ommended) should be connected from the Shutdown input
to the regulator input.

If the Shutdown input is driven from a source that actively
pulls high and low (like an op-amp), the pull-up resistor is not
required, but may be used.

If the shutdown function is not to be used, the cost of the
pull-up resistor can be saved by simply tying the Shutdown
input directly to the regulator input.

IMPORTANT: Since the Absolute Maximum Ratings state
that the Shutdown input can not go more than 0.3V below
ground, the reverse-battery protection feature which protects
the regulator input is sacrificed if the Shutdown input is tied
directly to the regulator input.

If reverse-battery protection is required in an application,

the

pull-up resistor between the Shutdown input and the regula-
tor input must be used.

Typical Applications

DS011128-37

* In shutdown mode, ERROR will go high if it has been pulled up to an
external supply. To avoid this invalid response, pull up to regulator output.

* Exact value depends on dropout voltage. (See Application Hints)

FIGURE 3. ERROR Output Timing

Typical Application Circuit

DS011128-1

5V Regulator

DS011128-6

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Physical Dimensions

inches (millimeters) unless otherwise noted (Continued)

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whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.

2. A critical component is any component of a life

support device or system whose failure to perform
can be reasonably expected to cause the failure of
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SO-8 Surface Mount Package

Order Number LP2954AIM or LP2954IM

NS Package Number M08A

LP2954/LP2954A

and

Adjustable

Micropower

Low-Dropout

oltage

Regulators

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.

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ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LP2954A