Datasheet LP4951CMX, LP4951CM Datasheet (NSC)

LP4950C-5V and LP4951C
Adjustable Micropower Voltage Regulators

General Description

The LP4950C and LP4951C are micropower voltage regu­lators with very low quiescent current (75µA typ.) and very
low dropout voltage (typ. 40mV at light loads and 380mV at
100mA). They are ideally suited for use in battery-powered
systems. Furthermore, the quiescent current of the
LP4950C/LP4951C increases only slightly in dropout, pro­longing battery life.

The LP4950C in the popular 3-pin TO-92 package is pin
compatible with older 5V regulators. The 8-lead LP4951C is
available in a plastic surface mount package and offers
additional system functions.

One such feature is an error flag output which warns of a low
output voltage, often due to falling batteries on the input. It
may be used for a power-on reset. A second feature is the
logic-compatible shutdown input which enables the regulator
to be switched on and off. Also, the part may be pin-strapped
for a 5V output or programmed from 1.24V to 29V with an
external pair of resistors.

Careful design of the LP4950C/LP4951C has minimized all
contributions to the error budget. This includes a tight initial

tolerance (.5% typ.), extremely good load and line regulation
(.05% typ.) and a very low output voltage temperature coef­ficient, making the part useful as a low-power voltage refer­ence.

Features

n High accuracy 5V guaranteed 100mA output
n Extremely low quiescent current
n Low dropout voltage
n Extremely tight load and line regulation
n Very low temperature coefficient
n Use as Regulator or Reference
n Needs only 1µF for stability
n Current and Thermal Limiting

LP4951C versions only

n Error flag warns of output dropout
n Logic-controlled electronic shutdown
n Output programmable from 1.24 to 29V

Block Diagram and Typical
Applications

LP4950C LP4951C

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September 2002

LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators

© 2002 National Semiconductor Corporation DS200528 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.

Input Supply Voltage −0.3 to +30V

SHUTDOWN Input Voltage,

Error Comparator Output
Voltage, (Note 9)

−0.3 to +30V

FEEDBACK Input Voltage −1.5 to +30V

(Note 9) (Note 10)

Power Dissipation Internally Limited

Junction Temperature (T

J

) +150˚C

Ambient Storage Temperature −65˚ to +150˚C

Soldering Dwell Time, Temperature

Wave
Infrared
Vapor Phase

4 seconds, 260˚C
10 seconds, 240˚C
75 seconds, 219˚C

ESD TBD

Operating Ratings (Note 1)

Maximum Input Supply Voltage 30V

Junction Temperature Range
(Note 8)

LP4950C, LP4951C −40˚C to 125˚C

Electrical Characteristics (Note 2)

Parameter

Conditions

(Note 2)

LP4950CZ

Units

LP4951CM

Tested Design

Typ Limit Limit

(Note 3) (Note 4)

Output Voltage T

J

= 25˚C 5.0 5.1 V max

4.9 V min

−25˚C ≤ T

J

≤ 85˚C 5.15 V max

4.85 V min

Full Operating 5.2 V max

Temperature Range 4.8 V min

Output Voltage 100 µA ≤ I

L

≤ 100 mA 5.24 V max

T

J

≤ T

JMAX

4.76 V min

Output Voltage
Temperature Coefficient

(Note 12) 150 ppm/˚C

Line Regulation
(Note 14)

6V ≤ V

IN

≤ 30V (Note 15) 0.04 0.2 % max

0.4 % max

Load Regulation
(Note 14)

100µA ≤ I

L

≤ 100mA 0.1 0.2 % max

0.3 % max

Dropout Voltage
(Note 5)

I

L

= 100µA 50 80 mV max

150 mV max

I

L

= 100mA 380 450 mV max

600 mV max

Ground Current I

L

= 100µA 75 150 µA max

170 µA max

I

L

= 100mA 8 15 mA max

19 mA max

Dropout Ground Current V

IN

= 4.5V 110 200 µA max

I

L

= 100µA 230 µA max

Current Limit V

OUT

= 0 160 200 mA max

220 mA max

Thermal Regulation (Note 13) 0.05 0.2 %/W max

Output Noise, C

L

= 1µF 430 µV rms

10 Hz to 100 kHz C

L

= 200µF 160 µV rms

C

L

= 3.3µF (Bypass = 0.01µF

Pins 7 to 1 (LP4951C)

100 µV rms

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Electrical Characteristics

LP4951C

Parameter Conditions (Note 2) Typ Tested

Limit (Note

3)

Desgin

Limit (Note

4)

Units

8-PIN VERSIONS ONLY

Reference Voltage 1.235 1.285 V max

1.295 V max

1.185 V min

1.165 Vmin

Reference Voltage (Note 7) 1.335 V max

1.135 V min

Feedback Pin Bias
Current

20 40 nA max

60 nA max

Reference Voltage
Temperature Coefficient

(Note 12) 50 ppm/˚C

Feedback Pin Bias
Current Temperature
Coefficient

0.1 nA/˚C

Error Comparator

Output Leakage Current VOH = 30V 0.01 1 µA max

2 µA max

Output Low Voltage V

IN

= 4.5V

I

OL

= 400µA

150 250 mV max

400 mV max

Upper Threshold Voltage (Note 4) 60 40 mV min

25 mV min

Lower Threshold Voltage (Note 6) 75 95 mV max

140 mV max

Hysteresis (Note 6) 15 mV

Shutdown Input

Input Logic Voltage 1.3 V

Low (Regulator ON) 0.7 V max

High (Regulator OFF) 2.0 V min

Shutdown Pin Input
Current

V

SHUTDOWN

= 2.4V 30 50 µA max

100 µA max

V

SHUTDOWN

= 30V 450 600 µA max

750 µA max

Regulator Output Current
in Shutdown

(Note 11) 3 10 µA max

20 µA max

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device

is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical
Characteristics tables.

Note 2: Unless otherwise specified all limits guaranteed for V

IN

=6V,IL= 100µA and CL= 1µF. Limits appearing in boldface type apply over the entire junction

temperature range for operation. Limits appearing in normal type apply for T

A=TJ

= 25˚C. Additional conditions for the 8-pin versions are FEEDBACK tied to V

TAP

,

OUTPUT tied to SENSE (V

OUT

= 5V), and V

SHUTDOWN

≤ 0.8V.

Note 3: Guaranteed and 100% production tested.

Note 4: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels.

Note 5: Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential.

At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account.

Note 6: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at V

IN

=

6V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = V

OUT/VREF

= (R1 + R2)/R2.For example, at a programmed
output voltage of 5V, the Error output is guaranteed to go low when the output drops by 95 mV x 5V/1.235V = 384 mV.Thresholds remain constant as a percent of
V

OUT

as V

OUT

is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed.

Note 7: V

REF

≤ V

OUT

≤ (VIN− 1V), 2.3V ≤ VIN≤ 30V, 100µA ≤ IL≤ 100mA, TJ≤ T

JMAX

.

Note 8: The junction-to-ambient thermal resistances are as follows: 180˚C/W and 160˚C/W for the TO-92 package with 0.40 inch and 0.25 inch leads to the printed
circuit board (PCB) respectively, 160˚C/W for the molded plastic SOP (M). The above thermal resistances for the M package apply when the package is soldered
directly to the PCB.

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Electrical Characteristics (Continued)

Note 9: May exceed input supply voltage.

Note 10: When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to

ground.

Note 11: V

SHUTDOWN

≥ 2V, VIN≤ 30V, V

OUT

= 0, Feedback pin tied to V

TAP

.

Note 12: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.

Note 13: 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 a 50 mA load pulse at V

IN

= 30V (1.25W pulse) for T = 10ms.

Note 14: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are
covered under the specification for thermal regulation.

Note 15: Line regulation for the LP4951C is tested at 150˚C for I

L

= 1 mA. For IL= 100µA and TJ= 125˚C, line regulation is guaranteed by design to 0.2%. See

Typical Performance Characteristics for line regulation versus temperature and load current.

Connection Diagrams

TO-92 Plastic Package (Z) Surface-Mount Package (M)

20052802

Bottom View

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Top View

Ordering Information

Package Output Voltage Temperature

5.0V

TO-92 (Z) LP4950CZ-5.0 −40˚C

<

T

J

<

125˚C

M (M08A) LP4951CM −40˚C

<

T

J

<

125˚C

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Typical Performance Characteristics

Quiescent Current Dropout Characteristics

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Input Current Input Current

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Output Voltage vs. Temperature of 3

Representative Units Quiescent Current

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Typical Performance Characteristics (Continued)

Quiescent Current Quiescent Current

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Quiescent Current Short Circuit Current

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Dropout Voltage Dropout Voltage

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Typical Performance Characteristics (Continued)

LP4951C Minimum Operating Voltage LP4951C Feedback Bias Current

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LP4951C Feedback Pin Current LP4951C Error Comparator Output

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LP4951C Comparator Sink Current Line Transient Response

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Typical Performance Characteristics (Continued)

Load Transient Response Load Transient Response

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LP4951C Enable Transient Output Impedance

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Ripple Rejection Ripple Rejection

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Typical Performance Characteristics (Continued)

Ripple Rejection Output Noise

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LP4951C Divider Resistance Shutdown Threshold Voltage

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Line Regulation LP4951C Maximum Rated Output Current

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Typical Performance Characteristics (Continued)

Thermal Response

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Application Hints

EXTERNAL CAPACITORS

A 1.0µF (or greater) capacitor is required between the output
and ground for stability at output voltages of 5V or more. At
lower output voltages, more capacitance is required. Without
this capacitor the part will oscillate. Most types of tantalum or
aluminum electrolytics work fine here; even film types work
but are not recommended for reasons of cost. Many alumi­num electrolytics have electrolytes that freeze at about

−30˚C, so solid tantalums are recommended for operation
below −25˚C. The important parameters of the capacitor are
an ESR of about 5 Ω or less and a resonant frequency above
500 kHz. The value of this capacitor may be increased
without limit.

At lower values of output current, less output capacitance is
required for stability. The capacitor can be reduced to

0.33 µF for currents below 10 mA or 0.1 µF for currents
below 1 mA. Using the 8-pin version at voltages below 5V
runs the error amplifier at lower gains so that more output
capacitance is needed. For the worst-case situation of a
100 mA load at 1.23V output (Output shorted to Feedback) a

3.3 µF (or greater) capacitor should be used.
Unlike many other regulators, the LP4950C will remain

stable and in regulation with no load in addition to the
internal voltage divider. This is especially important in CMOS
RAM keep-alive applications. When setting the output volt­age of the LP4951C version with external resistors, a mini­mum load of 1µA is recommended.

A 0.1µF capacitor should be placed from the LP4950C/
LP4951C input to ground if there is more than 10 inches of
wire between the input and the AC filter capacitor or if a
battery is used as the input.

Stray capacitance to the LP4951C Feedback terminal (pin 7)
can cause instability. This may especially be a problem when
using high value external resistors to set the output voltage.
Adding a 100pF capacitor between Output and Feedback
and increasing the output capacitor to at least 3.3µF will fix
this problem.

ERROR DETECTION COMPARATOR OUTPUT

The comparator produces a logic low output whenever the
LP4951C output falls out of regulation by more than approxi­mately 5%. This figure is the comparator’s built-in offset of
about 60 mV divided by the 1.235 reference voltage. (Refer
to the block diagram in the front of the datasheet.) This trip
level remains “5% below normal” regardless of the pro­grammed output voltage of the 4951C. For example, the
error flag trip level is typically 4.75V for a 5V output or 11.4V
for a 12V output. The out of regulation condition may be due
either to low input voltage, current limiting, or thermal limit­ing.

Figure 1 below gives a timing diagram depicting the ERROR
signal and the regulated output voltage as the LP4951C
input is ramped up and down. The ERROR signal becomes
valid (low) at about 1.3V input. It goes high at about 5V input
(the input voltage at which V

OUT

= 4.75V). Since the
LP4951C’s dropout voltage is load-dependent (see curve in
typical performance characteristics), the input voltage trip
point (about 5V) will vary with the load current. The output
voltage trip point (approx. 4.75V) does not vary with load.

The error comparator has an open-collector output which
requires an external pullup resistor. This resistor may be
returned to the output or some other supply voltage depend­ing on system requirements. In determining a value for this
resistor, note that while the output is rated to sink 400µA, this
sink current adds to battery drain in a low battery condition.
Suggested values range from 100k to 1 MΩ. The resistor is
not required if this output is unused.

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Application Hints (Continued)

PROGRAMMING THE OUTPUT VOLTAGE (LP4951C)

The LP4951C may be pin-strapped for 5V using its internal
voltage divider by tying the pin 1 (output) to pin 2 (sense)
pins together, and also tying the pin 7 (feedback) and pin 6
(V

TAP

) pins together. Alternatively, it may be programmed for
any output voltage between its 1.235V reference and its 30V
maximum rating. As seen in Figure 2, an external pair of
resistors is required.

The complete equation for the output voltage is

where V

REF

is the nominal 1.235 reference voltage and IFBis
the feedback pin bias current, nominally −20 nA. The mini­mum recommended load current of 1µA forces an upper limit
of 1.2 MΩ on the value of R

2

, if the regulator must work with

no load (a condition often found in CMOS in standby). I

FB

will

produce a 2% typical error in V

OUT

which may be eliminated

at room temperature by trimming R

1

. For better accuracy,

choosing R

2

= 100k reduces this error to 0.17% while in­creasing the resistor program current to 12µA. Since the
LP4951C typically draws 60µA at no load with Pin 2 open­circuited, this is a small price to pay.

REDUCING OUTPUT NOISE

In reference applications it may be advantageous to reduce
the AC noise present at the output. One method is to reduce
the regulator bandwidth by increasing the size of the output
capacitor. This is the only way noise can be reduced on the
3 lead LP4950C but is relatively inefficient, as increasing the
capacitor from 1µF to 220µF only decreases the noise from
430µV to 160µV rms for a 100kHz bandwidth at 5V output.

Noise can be reduced fourfold by a bypass capacitor across
R

1

, since it reduces the high frequency gain from 4 to unity.

Pick

or about 0.01µF. When doing this, the output capacitor must
be increased to 3.3µF to maintain stability. These changes
reduce the output noise from 430µV to 100µV rms for a
100kHz bandwidth at 5V output. With the bypass capacitor
added, noise no longer scales with output voltage so that
improvements are more dramatic at higher output voltages.

20052820

*

When VIN≤ 1.3V, the error flag pin becomes a high impedance, and the

error flag voltage rises to its pull-up voltage. Using V

OUT

as the pull-up
voltage (see Figure 2), rather than an external 5V source, will keep the
error flag voltage under 1.2V (typ.) in this condition. The user may wish to
divide down the error flag voltage using equal-value resistors (10 kΩ
suggested), to ensure a low-level logic signal during any fault condition,
while still allowing a valid high logic level during normal operation.

FIGURE 1. ERROR Output Timing

20052807

*

See Application Hints

**

Drive with TTL-high to shut down. Ground or leave open if shutdown

feature is not to be used.

Note: Pins 2 and 6 are left open.

FIGURE 2. Adjustable Regulator (LP4951C)

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Schematic Diagram

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Physical Dimensions inches (millimeters)

unless otherwise noted

Surface Mount Package (M)

NS Package Number M08A

Molded TO-92 Package (Z)
NS Package Number Z03A

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Notes

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COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

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significant injury to the user.

2. A critical component is any component of a life
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can be reasonably expected to cause the failure of
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LP4950C-5V and LP4951C Adjustable Micropower Voltage 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.