Datasheet LP2954, LP2954A Datasheet (National Semiconductor)

Page 1

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

April 2005

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 threelead 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 network 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.

Package Outline and Ordering Information

TO-220 3– Lead Plastic Package

Features

n 5V output within 1.2% over temperature (A grade) n Adjustable 1.23 to 29V output voltage available

(LP2954IM and LP2954AIM)

n Guaranteed 250 mA output current n Extremely low quiescent current n Low dropout voltage n Reverse battery protection n Extremely tight line and load regulation n Very low temperature coefficient n Current and thermal limiting n Pin compatible with LM2940 and LM340 (5V version

only)

n Adjustable version adds error flag to warn of output drop

and a logic-controlled shutdown

Applications

n High-efficiency linear regulator n Low dropout battery-powered regulator

TO-263 3-Lead Plastic Surface-Mount Package

Top View

Front View

Order Number LP2954AIT or LP2954IT

See NS Package T03B

SO-8 Small Outline Surface Mount

Top View

Order Number LP2954AIM or LP2954IM

See NS Package M08A

01112802

Side View

Order Number LP2954AIS or LP2954IS

See NS Package TS3B

01112833

01112809

01112810

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Ordering Information

Order Number Temp. Range Package NS Package

) ˚C (JEDEC) Number

LP2954AIT −40 to +125 TO-220 TO3B

LP2954IT

LP2954AIS −40 to +125 TO-263 TS3B

LP2954/LP2954A 5V

LP2954IS

LP2954AIM −40 to +125 SO-8 M08A

LP2954IM

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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

Electrical Characteristics

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

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Electrical Characteristics (Continued)

Limits in standard typeface are for TJ= 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. Unless otherwise noted: V

Symbol Parameter Conditions Typical 2954AI 2954I Units

LP2954/LP2954A 5V

Output Noise CL= 2.2 µF 400 µV RMS

Voltage

(10 Hz to 100 kHz) C

= 100 mA

Additional Specifications for the Adjustable Device (LP2954AIM and LP2954IM)

∆V

REF

Reference Voltage (Note 10) 1.230 1.215

REF

Reference Voltage

REF

Line Regulation

REF

/∆T Reference Voltage

Temperature Coefficient

(FB) Feedback Pin Bias

Current

GND

Ground Pin Current at Shutdown (Note 6)

(SINK) Output "OFF"

Pulldown Current

Dropout Detection Comparator

Output "HIGH" Leakage Current

THR

Output "LOW" Voltage VIN=VO(NOM)−0.5V

(MAX) Upper Threshold

Voltage

(MIN) Lower Threshold

THR

Voltage

HYST Hysteresis (Note 13) 15 mV

Shutdown Input

Input Offset Voltage (Referred to V

HYST Hysteresis 6 mV

Input Bias Current VIN(S/D)=0V to 5V 10 −30

= 6V, IL= 1 mA, CL= 2.2 µF.

=33µF 260

=33µF(Note 9) 80

VIN=2.5V to VO(NOM)+1V

VIN=2.5V to VO(NOM)+1V to 30V (Note 11)

(Note 3) 20 ppm/˚C

SHUTDOWN

≤1.1V 105 140 140 µA

(Note 12) 30

VOH=30V 0.01 1

(COMP)=400µA

(Note 13) −60 −80

(Note 13) −85 −110

REF

Min Max Min Max

1.205

1.245

1.255

1.205

1.190

1.255

1.270

0.03 0.1 0.2 %

0.2 0.4 %

20 40

150 250

400

−35

−95

−25

−55

−160

)

3 −7.5

−10

−40

7.5

−50

−80

−95

−110

−160

−7.5

−10

−30

−50

250

400

−35

−25

−55

−40

7.5

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

device outside of its rated operating conditions.

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

Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. The junction-toambient 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 resistance can be reduced by increasing the P.C. board copper area thermally connected to the package: Using 0.5 square inches of copper area, θ 50˚C/W; with 1 square inch of copper area, θ 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 resistance of the heatsink selected, and the thermal resistance of the interface between the heatsink and the LP2954. Some typical values are listed for interface materials used with TO-220:

TABLE 1. Typical Values of Case-to-Heatsink

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

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

is 37˚C/W; and with 1.6 or more square inches of copper area, θJAis 32˚C/W. The junction-to-case thermal resistance

TABLE 2. Typical Values of Case-to-Heatsink

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

Silicone grease 1.0

Dry interface 1.3

Mica with grease 1.4

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 mA–1 mA and 1 mA–250 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

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

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

Note 12: V

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

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

REF≤VOUT

SHUTDOWN

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

IN=VO

≤(VIN−1V), 2.3V≤VIN≤30V, 100µA≤IL≤250mA.

≤1.1V, VOUT=VO(NOM).

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

=2.5V to VO(NOM)+1V and the other test for VIN=2.5V to VO(NOM)+1V to 30V.

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

Thermasil III 1.3

Thermasil II 1.5

Thermalfilm (0.002) with grease 2.2

=(R1+R2)/R2.

OUT/VREF

J-A

LP2954/LP2954A 5V

Typical Performance Characteristics

Quiescent Current Quiescent Current

01112812 01112813

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Typical Performance Characteristics (Continued)

Ground Pin Current vs Load Ground Pin Current

LP2954/LP2954A 5V

01112814

Ground Pin Current Output Noise Voltage

01112816

Ripple Rejection Ripple Rejection

01112815

01112817

01112818

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01112819

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Typical Performance Characteristics (Continued)

Ripple Rejection Line Transient Response

LP2954/LP2954A 5V

01112820

Line Transient Response Output Impedance

01112822

Load Transient Response Load Transient Response

01112821

01112823

01112824 01112825

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Typical Performance Characteristics (Continued)

Dropout Characteristics Thermal Response

01112826

Short-Circuit Output

Current and Maximum

Output Current

01112828

Application Hints

EXTERNAL CAPACITORS

A 2.2 µF (or greater) capacitor is required between the output 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 electrolytics contain electrolytes which freeze at −30˚C, which requires the use of solid tantalums below −25˚C. The important parameters of the capacitor are an ESR of about 5Ω or less and a resonant frequency above 500 kHz (the ESR may increase 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 increased 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 input 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

01112827

Maximum Power Dissipation

(TO-263) (See (Note 2) )

01112811

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 instability. This problem is most likely to appear when using high value external resistors to set the 2379-307.2(a9-307.2(a9-3-235(Addsing)-.2(a9aw)]TJT*[(100)-5(3.(pF0)-5(3.((capacitor)-5(3.((between)-5(3.((the)-5(3.(Ooutput)-5(3.((and)-5(3.((Feedback)-5(3.(pains)]TJT*[(and)-304.4(increasing)-304.4(the)-304.4(output)-304.4(capacitance)-034.4(to)-034.4(6.8)-034.4(µF)-034.4((or)-034.4gcretger))]TJT*[(will)-332.8(cube)-332.8(the)-332.8(proble.f)]TJ/F1 1 Tf0 21.3713 TD[MINIMUMe)-332.8LOADf)]TJ/21 1 Tf0 -1.5 TD[Wwhen)-636.2(setsing)-636.2(the)-636.2(output)-636.2-307.2(t)-636.2(using)-636.2aen)-636.2(external)-636.2(resissiv-)]TJ0 -1.2143 TD[dividwer542.8t,)-226.2a,)-226.2(minimum)-226.2(currenm)-226.2(of)-226.21f)-226.2µA)0mA)-347.4iA)0sf)-226.2recommendced)-226.2thgroigh)]TJT*[(the)-332.8(resistors)-332.8(oe)-332.8(prvidw,)-332.8(a)-332.8(minimum)-332.8(load.)]TJ0 -1.5 TD[Iut)-249.2(should)-249.2(bd)-249.2noteld thut minimum load currenm

of the eost tish valueusteoe thsueeossed limis(.)-279.1(Tce)-324.9parte is eosred to 100

witl load.

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Application Hints (Continued)

DROPOUT VOLTAGE

The dropout voltage of the regulator is defined as the minimum input-to-output voltage differential required for the output voltage to stay within 100 mV of the output voltage measured with a 1V differential. The dropout voltages for various values of load current are listed under Electrical Characteristics.

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, including 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 temperature of the application. Under all possible operating conditions, 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 produces the maximum DC input voltage to the regulator). Figure 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.

lated value is below 60˚ C/W, an external heatsink is required. The required thermal resistance for this heatsink can be calculated using the formula:

= θ

− θ

(H-A)

(J-A)

(J-C)

− θ

(C-H)

where:

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

(J-C)

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

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

(C-H)

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.

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

(H-A)

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 θ

calculated from the

(H-A)

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 together.

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 equation for the output voltage is:

where V

is the 1.23V reference and IFBis the Feedback

REF

pin bias current (−20 nA typical). The minimum recommended load current of 1 µA sets an upper limit of 1.2 MΩ on the value of R2 in cases where the regulator must work with no load (see MINIMUM LOAD ). I error in V

which can be eliminated at room temperature

OUT

will produce a typical 2%

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

LP2954/LP2954A 5V

*See External Capacitors

=(VIN−5) IL+(VIN)I

Total

01112805

FIGURE 1. Basic 5V Regulator Circuit

The next parameter which must be calculated is the maximum allowable temperature rise, T

(max). This is calculated

by using the formula:

(max) = TJ(max) − TA(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

required value for junction-to-ambient thermal resistance,

, can now be found:

(J-A)

(J-A)=TR

(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-

* See Application Hints

01112836

** Drive with TTL-low to shut down

FIGURE 2. Adjustable Regulator

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Application Hints (Continued)

DROPOUT DETECTION COMPARATOR

This comparator produces a logic “LOW” whenever the output 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

LP2954/LP2954A 5V

programmed output voltage. An out-of-regulation condition can result from low input voltage, current limiting, or thermal limiting.

Figure 3 gives a timing diagram showing the relationship between the output voltage, the ERROR output, and input voltage as the input voltage is ramped up and down to a regulator 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 comparator 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 kΩ to 1 MΩ. This resistor is not required if the output is unused.

When V ance, allowing the error flag voltage to rise to its pull-up voltage. Using V external 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 kΩ suggested) to ensure a low-level logic signal during any fault condition, while still allowing a valid high logic level during normal operation.

* 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)

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

as the pull-up voltage (rather than an

OUT

01112837

OUTPUT ISOLATION

The regulator output can be left connected to an active voltage source (such as a battery) with the regulator input power turned off, as long as the regulator ground pin is

connected 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 selecting 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 stability. 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 improvements 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. If the input is driven from opencollector logic, a pull-up resistor (20 kΩ to 100 kΩ recommended) 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 regulator input must be used.

FIGURE 3. ERROR Output Timing

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Typical Applications

LP2954/LP2954A 5V

Typical Application Circuit

01112801

5V Regulator

01112806

5V Current Limiter

*Output voltage equals +VINminus dropout voltage, which varies with output current. Current limits at 380 mA (typical).

01112807

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Schematic Diagram

LP2954/LP2954A 5V

01112808

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Physical Dimensions inches (millimeters)

unless otherwise noted

LP2954/LP2954A 5V

TO-220 3-Lead Plastic Package

Order Number LP2954AIT or LP2954IT

NS Package T03B

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Physical Dimensions inches (millimeters) unless otherwise noted (Continued)

LP2954/LP2954A 5V

TO-263 3-Lead Plastic Surface Mount Package

Order Number LP2954AIS or LP2954IS

NS Package TS3B

SO-8 Surface Mount Package

Order Number LP2954AIM or LP2954IM

NS Package Number M08A

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Notes

LP2954/LP2954A 5V and Adjustable Micropower Low-Dropout 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.

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