LM3915芯片引脚定义引脚图及功能IC贸易商引脚图技术参数-中国IC网-芯三七

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产品型号LM3915的概述

LM3915的概述 LM3915是一款由德州仪器（Texas Instruments）公司制造的集成电路，主要用于电压等级指示和灯光控制。这款芯片内置了一个10段LED显示控制器，可以将输入的模拟电压转换为相应的LED亮度，广泛应用于音量表、电流表和其他需要视觉指示的设备。它的设计既方便又可靠，适用于各类电子项目。该芯片的工作原理是通过将输入电压分为十个级别，并控制相应数量的LED灯点亮。例如，如果输入电压为5V，则会点亮5个LED。LM3915可以在两种模式下工作：点亮模式（LED亮起）和条形图模式（LED条形显示）。这种灵活性使其在各种应用中都能表现良好。 LM3915的详细参数 LM3915的主要参数包括： - 工作电压范围：3V至25V - 输出电流：每个LED输出电流最大可达到30mA - 环境温度范围：-40℃至85℃ - 输入电压类型：可接受从0V至Vref的浓度 - ...

产品型号LM3915的Datasheet PDF文件预览

January 2000

LM3915

Dot/Bar Display Driver

The LM3915 is very versatile. The outputs can drive LCDs,

vacuum fluorescents and incandescent bulbs as well as

LEDs of any color. Multiple devices can be cascaded for a

dot or bar mode display with a range of 60 or 90 dB.

LM3915s can also be cascaded with LM3914s for a linear/

log display or with LM3916s for an extended-range VU

meter.

General Description

The LM3915 is a monolithic integrated circuit that senses

analog voltage levels and drives ten LEDs, LCDs or vacuum

fluorescent displays, providing a logarithmic 3 dB/step ana-

log display. One pin changes the display from a bar graph to

a moving dot display. LED current drive is regulated and pro-

grammable, eliminating the need for current limiting resis-

tors. The whole display system can operate from a single

supply as low as 3V or as high as 25V.

Features

n 3 dB/step, 30 dB range

n Drives LEDs, LCDs, or vacuum fluorescents

n Bar or dot display mode externally selectable by user

n Expandable to displays of 90 dB

The IC contains an adjustable voltage reference and an ac-

curate ten-step voltage divider. The high-impedance input

buffer accepts signals down to ground and up to within 1.5V

of the positive supply. Further, it needs no protection against

inputs of 35V. The input buffer drives 10 individual com-

n Internal voltage reference from 1.2V to 12V

n Operates with single supply of 3V to 25V

n Inputs operate down to ground

parators referenced to the precision divider. Accuracy is typi-

cally better than 1 dB.

The LM3915’s 3 dB/step display is suited for signals with

wide dynamic range, such as audio level, power, light inten-

sity or vibration. Audio applications include average or peak

level indicators, power meters and RF signal strength

meters. Replacing conventional meters with an LED bar

graph results in a faster responding, more rugged display

with high visibility that retains the ease of interpretation of an

analog display.

n Output current programmable from 1 mA to 30 mA

n Input withstands 35V without damage or false outputs

n Outputs are current regulated, open collectors

n Directly drives TTL or CMOS

n The internal 10-step divider is floating and can be

referenced to a wide range of voltages

The LM3915 is rated for operation from 0˚C to +70˚C. The

LM3915N-1 is available in an 18-lead molded DIP package.

The LM3915 is extremely easy to apply. A 1.2V full-scale

meter requires only one resistor in addition to the ten LEDs.

One more resistor programs the full-scale anywhere from

1.2V to 12V independent of supply voltage. LED brightness

is easily controlled with a single pot.

DS005104

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Typical Applications

0V to 10V Log Display

DS005104-1

Notes: Capacitor C1 is required if leads to the LED supply are 6" or longer.

Circuit as shown is wired for dot mode. For bar mode, connect pin 9 to pin 3. V

dissipation.

must be kept below 7V or dropping resistor should be used to limit IC power

LED

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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.

Voltage on Output Drivers

Input Signal Overvoltage (Note 4)

Divider Voltage

25V

35V

−100 mV to V⁺

Reference Load Current

Storage Temperature Range

10 mA

−55˚C to +150˚C

Power Dissipation (Note 6)

Molded DIP(N)

1365 mW

25V

Lead Temperature

(Soldering, 10 sec.)

260˚C

Supply Voltage

Electrical Characteristics (Notes 2, 4)

Parameter

Conditions (Note 2)

Min

Typ

Max

Units

COMPARATOR

0V ≤ V_RLOV_RHI≤ 12V,

Offset Voltage, Buffer and First

Comparator

I_LED1 mA

0V ≤ V_RLOV_RHI≤ 12V,

Offset Voltage, Buffer and Any Other

Comparator

I_LED1 mA

Gain (∆I_LED/∆V_IN

)

I_L(REF)2 mA, I_LED10 mA

0V ≤ V_IN≤ (V⁺− 1.5V)

No Change in Display

mA/mV

Input Bias Current (at Pin 5)

Input Signal Overvoltage

VOLTAGE-DIVIDER

100

−35

Divider Resistance

Total, Pin 6 to 4

(Note 3)

kΩ

Relative Accuracy (Input Change

Between Any Two Threshold Points)

2.0

3.0

4.0

Absolute Accuracy at Each Threshold

Point

(Note 3)

V_IN= −3, −6 dB

−0.5

+0.5

+0.65

+1.0

V_IN= −9 dB

V_IN= −12, −15, −18 dB

V_IH= −21, −24, −27 dB

+1.5

VOLTAGE REFERENCE

Output Voltage

0.1 mA ≤ I_L(REF)≤ 4 mA,

1.2

1.28

0.01

0.4

1.34

0.03

V⁺V_LED5V

3V ≤ V⁺≤ 18V

Line Regulation

Load Regulation

0.1 mA ≤ I_L(REF)≤ 4 mA,

V⁺V_LED5V

0˚C ≤ T_A≤ +70˚C, I_L(REF)1 mA,

Output Voltage Change with

Temperature

V_LED5V

Adjust Pin Current

OUTPUT DRIVERS

LED Current

120

µA

V_LED5V, I_L(REF)1 mA

0.12

1.2

0.1

0.4

V_LED= 5V, I_LED2 mA

V_LED= 5V, I_LED20 mA

LED Current Difference (Between

Largest and Smallest LED Currents)

LED Current Regulation

2V ≤ V_LED≤ 17V, I_LED= 2 mA

I_LED= 20 mA

0.25

Dropout Voltage

I_LED(ON)20 mA, V_LED5V,

∆I_LED2 mA

1.5

Saturation Voltage

I_LED2.0 mA, I_L(REF)0.4 mA

0.15

0.1

0.4

Output Leakage, Each Collector

(Bar Mode) (Note 5)

µA

Output Leakage

Pins 10–18

(Dot Mode) (Note 5)

0.1

µA

Pin 1

150

450

SUPPLY CURRENT

V⁺+5V, I_L(REF)0.2 mA

V⁺+20V, I_L(REF)1.0 mA

2.4

6.1

4.2

9.2

Standby Supply Current

(All Outputs Off)

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Electrical Characteristics (Notes 2, 4) (Continued)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-

tional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guar-

antee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is

given, however, the typical value is a good indication of device performance.

Note 2: Unless otherwise stated, all specifications apply with the following conditions:

25˚C, I

L(REF)

3 V

≤ V ≤ 20 V

−0.015V ≤ V

≤ 12 V

0.2 mA, pin 9 connected to pin 3 (bar mode).

RLO

≤ V

, V , V

≤ (V − 1.5V)

For higher power dissipations, pulse testing is used.

LED

REF

RHI

−0.015V ≤ V

≤ 12 V

0V ≤ V ≤ V − 1.5V

RHI

Note 3: Accuracy is measured referred to 0 dB + 10.000 V at pin 5, with + 10.000 V at pin 6, and 0.000 V at pin 4. At lower full scale voltages, buffer and

comparator offset voltage may add significant error. See table for threshold voltages.

Note 4: Pin 5 input current must be limited to 3 mA. The addition of a 39k resistor in series with pin 5 allows 100V signals without damage.

Note 5: Bar mode results when pin 9 is within 20 mV of V . Dot mode results when pin 9 is pulled at least 200 mV below V . LED #10 (pin 10 output current) is dis-

abled if pin 9 is pulled 0.9V or more below V

LED

Note 6: The maximum junction temperature of the LM3915 is 100˚C. Devices must be derated for operation at elevated temperatures. Junction to ambient thermal

resistance is 55˚C/W for the molded DIP (N package).

Threshold Voltage (Note 3)

Output

−27

−24

−21

−18

−15

Min

Typ

Max

Output

−12

−9

−6

−3

Min

Typ

2.512

3.548

5.012

7.079

Max

2.819

3.825

5.309

7.498

10.015

0.422

0.596

0.841

1.189

1.679

0.447

0.631

0.891

1.259

1.778

0.531

0.750

1.059

1.413

1.995

2.372

3.350

4.732

6.683

9.985

Typical Performance Characteristics

Supply Current vs Temperature

Operating Input Bias Current vs

Temperature

Reference Voltage vs

Temperature

DS005104-34

DS005104-35

DS005104-36

Reference Adjust Pin

Current vs Temperature

LED Current-Regulation

Dropout

LED Driver Saturation

Voltage

DS005104-37

DS005104-38

DS005104-39

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Typical Performance Characteristics (Continued)

Input Current Beyond

Signal Range (Pin 5)

LED Current vs

Reference Loading

LED Driver Current

Regulation

DS005104-40

DS005104-41

DS005104-42

Total Divider Resistance

vs Temperature

Common-Mode Limits

Output Characteristics

DS005104-45

DS005104-44

DS005104-43

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Block Diagram (Showing Simplest Application)

DS005104-4

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Functional Description

LM3915 Output Circuit

The simplified LM3915 block diagram is included to give the

general idea of the circuit’s operation. A high input imped-

ance buffer operates with signals from ground to 12V, and is

protected against reverse and overvoltage signals. The sig-

nal is then applied to a series of 10 comparators; each of

which is biased to a different comparison level by the resistor

string.

In the example illustrated, the resistor string is connected to

the internal 1.25V reference voltage. In this case, for each

3 dB that the input signal increases, a comparator will switch

on another indicating LED. This resistor divider can be con-

nected between any 2 voltages, providing that they are at

least 1.5V below V⁺and no lower than V⁻.

DS005104-6

Outputs may be run in saturation with no adverse effects,

making it possible to directly drive logic. The effective satura-

tion resistance of the output transistors, equal to R_Eplus the

transistors’ collector resistance, is about 50Ω. It’s also pos-

sible to drive LEDs from rectified AC with no filtering. To

avoid oscillations, the LED supply should be bypassed with a

2.2 µF tantalum or 10 µF aluminum electrolytic capacitor.

INTERNAL VOLTAGE REFERENCE

The reference is designed to be adjustable and develops a

nominal 1.25V between the REF OUT (pin 7) and REF ADJ

(pin 8) terminals. The reference voltage is impressed across

program resistor R1 and, since the voltage is constant, a

constant current I₁then flows through the output set resistor

R2 giving an output voltage of:

MODE PIN USE

Pin 9, the Mode Select input, permits chaining of multiple

LM3915s, and controls bar or dot mode operation. The fol-

lowing tabulation shows the basic ways of using this input.

Other more complex uses will be illustrated in the applica-

tions.

Bar Graph Display: Wire Mode Select (pin 9) directly to pin

3 (V⁺pin).

Dot Display, Single LM3915 Driver: Leave the Mode Select

pin open circuit.

Dot Display, 20 or More LEDs: Connect pin 9 of the first

driver in the series (i.e., the one with the lowest input voltage

comparison points) to pin 1 of the next higher LM3915 driver.

Continue connecting pin 9 of lower input drivers to pin 1 of

higher input drivers for 30 or more LED displays. The last

LM3915 driver in the chain will have pin 9 left open. All pre-

vious drivers should have a 20k resistor in parallel with LED

DS005104-5

9 (pin 11 to V_LED).

Since the 120 µA current (max) from the adjust terminal rep-

resents an error term, the reference was designed to mini-

mize changes of this current with V⁺and load changes. For

correct operation, reference load current should be between

80 µA and 5 mA. Load capacitance should be less than

0.05 µF.

Mode Pin Functional Description

This pin actually performs two functions. Refer to the simpli-

fied block diagram below.

Block Diagram of Mode Pin Function

CURRENT PROGRAMMING

A feature not completely illustrated by the block diagram is

the LED brightness control. The current drawn out of the ref-

erence voltage pin (pin 7) determines LED current. Approxi-

mately 10 times this current will be drawn through each

lighted LED, and this current will be relatively constant de-

spite supply voltage and temperature changes. Current

drawn by the internal 10-resistor divider, as well as by the ex-

ternal current and voltage-setting divider should be included

in calculating LED drive current. The ability to modulate LED

brightness with time, or in proportion to input voltage and

other signals can lead to a number of novel displays or ways

of indicating input overvoltages, alarms, etc.

The LM3915 outputs are current-limited NPN transistors as

shown below. An internal feedback loop regulates the tran-

sistor drive. Output current is held at about 10 times the ref-

erence load current, independent of output voltage and pro-

cessing variables, as long as the transistor is not saturated.

DS005104-7

High for bar

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OTHER DEVICE CHARACTERISTICS

Mode Pin Functional Description

The LM3916 is relatively low-powered itself, and since any

number of LEDs can be powered from about 3V, it is a very

efficient display driver. Typical standby supply current (all

LEDs OFF) is 1.6 mA. However, any reference loading adds

4 times that current drain to the V⁺(pin 3) supply input. For

example, an LM3916 with a 1 mA reference pin load (1.3k)

would supply almost 10 mA to every LED while drawing only

10 mA from its V⁺pin supply. At full-scale, the IC is typically

(Continued)

DOT OR BAR MODE SELECTION

The voltage at pin 9 is sensed by comparator C1, nominally

referenced to (V⁺− 100 mV). The chip is in bar mode when

pin 9 is above this level; otherwise it’s in dot mode. The com-

parator is designed so that pin 9 can be left open circuit for

dot mode.

drawing less than 10 of the current supplied to the display.

Taking into account comparator gain and variation in the

100 mV reference level, pin 9 should be no more than 20 mV

below V⁺for bar mode and more than 200 mV below V⁺(or

open circuit) for dot mode. In most applications, pin 9 is ei-

ther open (dot mode) or tied to V⁺(bar mode). In bar mode,

pin 9 should be connected directly to pin 3. Large currents

drawn from the power supply (LED current, for example)

should not share this path so that large IR drops are avoided.

The display driver does not have built-in hysteresis so that

the display does not jump instantly from one LED to the next.

Under rapidly changing signal conditions, this cuts down

high frequency noise and often an annoying flicker. An “over-

lap” is built in so that at no time are all segments completely

off in the dot mode. Generally 1 LED fades in while the other

fades out over a mV or more of range. The change may be

much more rapid between LED #10 of one device and LED

1 of a second device “chained” to the first.

DOT MODE CARRY

In order for the display to make sense when multiple

LM3915s are cascaded in dot mode, special circuitry has

been included to shut off LED #10 of the first device when

Application Hints

The most difficult problem occurs when large LED currents

are being drawn, especially in bar graph mode. These cur-

rents flowing out of the ground pin cause voltage drops in ex-

ternal wiring, and thus errors and oscillations. Bringing the

return wires from signal sources, reference ground and bot-

tom of the resistor string to a single point very near pin 2 is

the best solution.

LED 1 of the second device comes on. The connection for

cascading in dot mode has already been described and is

depicted below.

As long as the input signal voltage is below the threshold of

the second LM3915, LED 11 is off. Pin 9 of LM3915 1 thus

sees effectively an open circuit so the chip is in dot mode. As

soon as the input voltage reaches the threshold of LED 11,

Long wires from V_LEDto LED anode common can cause os-

cillations. Depending on the severity of the problem 0.05 µF

to 2.2 µF decoupling capacitors from LED anode common to

pin 2 will damp the circuit. If LED anode line wiring is inac-

cessible, often similar decoupling from pin 1 to pin 2 will be

sufficient.

pin 9 of LM3915 1 is pulled an LED drop (1.5V or more) be-

low V_LED. This condition is sensed by comparator C2, refer-

enced 600 mV below V_LED. This forces the output of C2 low,

which shuts off output transistor Q2, extinguishing LED 10.

_LEDis sensed via the 20k resistor connected to pin 11. The

very small current (less than 100 µA) that is diverted from

If LED turn ON seems slow (bar mode) or several LEDs light

(dot mode), oscillation or excessive noise is usually the prob-

lem. In cases where proper wiring and bypassing fail to stop

oscillations, V⁺voltage at pin 3 is usually below suggested

limits. Expanded scale meter applications may have one or

both ends of the internal voltage divider terminated at rela-

tively high value resistors. These high-impedance ends

should be bypassed to pin 2 with at least a 0.001 µF capaci-

tor, or up to 0.1 µF in noisy environments.

LED 9 does not noticeably affect its intensity.

An auxiliary current source at pin 1 keeps at least 100 µA

flowing through LED 11 even if the input voltage rises high

enough to extinguish the LED. This ensures that pin 9 of

LM3915 1 is held low enough to force LED 10 off when

any higher LED is illuminated. While 100 µA does not nor-

mally produce significant LED illumination, it may be notice-

able when using high-efficiency LEDs in a dark environment.

If this is bothersome, the simple cure is to shunt LED 11

with a 10k resistor. The 1V IR drop is more than the 900 mV

worst case required to hold off LED 10 yet small enough

that LED 11 does not conduct significantly.

Cascading LM3915s in Dot Mode

DS005104-8

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negative signal differs by only 0.5 dB worst case. Substitut-

Application Hints (Continued)

ing 5 resistors increases this to 2 dB worst case. (A 2 dB

Power dissipation, especially in bar mode should be given

consideration. For example, with a 5V supply and all LEDs

programmed to 20 mA the driver will dissipate over 600 mW.

In this case a 7.5Ω resistor in series with the LED supply will

cut device heating in half. The negative end of the resistor

should be bypassed with a 2.2 µF solid tantalum capacitor to

pin 2.

gain difference means that the display may have a 1 dB er-

ror when the input is a nonsymmetrical transient). The aver-

aging time constant is R5–C2. A simple modification results

in the precision full-wave detector of Figure 4. Since the filter

capacitor is not buffered, this circuit can drive only high im-

pedance loads such as the input of an LM3915.

TIPS ON RECTIFIER CIRCUITS

The simplest way to display an AC signal using the LM3915

is to apply it right to pin 5 unrectified. Since the LED illumi-

nated represents the instantaneous value of the AC wave-

form, one can readily discern both peak and average values

of audio signals in this manner. The LM3915 will respond to

positive half-cycles only but will not be damaged by signals

up to 35V (or up to 100V if a 39k resistor is in series with

the input). It’s recommended to use dot mode and to run the

LEDs at 30 mA for high enough average intensity.

True average or peak detection requires rectification. If an

LM3915 is set up with 10V full scale across its voltage di-

vider, the turn-on point for the first LED is only 450 mV. A

simple silicon diode rectifier won’t work well at the low end

due to the 600 mV diode threshold. The half-wave peak de-

tector in Figure 1 uses a PNP emitter-follower in front of the

diode. Now, the transistor’s base-emitter voltage cancels out

the diode offset, within about 100 mV. This approach is usu-

ally satisfactory when a single LM3915 is used for a 30 dB

display.

DS005104-9

DC Couple

FIGURE 1. Half-Wave Peak Detector

Display circuits using two or more LM3915s for a dynamic

range of 60 dB or greater require more accurate detection. In

the precision half-wave rectifier of Figure 2 the effective di-

ode offset is reduced by a factor equal to the open-loop gain

of the op amp. Filter capacitor C2 charges through R3 and

discharges through R2 and R3, so that appropriate selection

of these values results in either a peak or an average detec-

tor. The circuit has a gain equal to R2/R1.

DS005104-10

It’s best to capacitively couple the input. Audio sources fre-

quently have a small DC offset that can cause significant er-

ror at the low end of the log display. Op amps that slew

quickly, such as the LF351, LF353, or LF356, are needed to

faithfully respond to sudden transients. It may be necessary

to trim out the op amp DC offset voltage to accurately cover

a 60 dB range. Best results are obtained if the circuit is ad-

justed for the correct output when a low-level AC signal

(10 mV to 20 mV) is applied, rather than adjusting for zero

output with zero input.

D1, D2: 1N914 or 1N4148

Average Peak

100k

R1 R2 for A

R1 R2/R10 for A

C1 10/R1

FIGURE 2. Precision Half-Wave Rectifier

For precision full-wave averaging use the circuit in Figure 3.

Using 1 resistors for R1 through R4, gain for positive and

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Application Hints (Continued)

DS005104-11

D1, D2: 1N914 or 1N4148

FIGURE 3. Precision Full-Wave Average Detector

DS005104-12

D1, D2, D3, D4: 1N914 or 1N4148

FIGURE 4. Precision Full-Wave Peak Detector

CASCADING THE LM3915

A better approach shown in Figure 6 is to keep the reference

at 10V for both LM3915s and amplify the input signal to the

To display signals of 60 dB or 90 dB dynamic range, multiple

LM3915s can be easily cascaded. Alternatively, it is possible

to cascade an LM3915 with LM3914s for a log/linear display

or with an LM3916 to get an extended range VU meter.

lower LM3915 by 30 dB. Since two 1 resistors can set the

amplifier gain within 0.2 dB, a gain trim is unnecessary.

However, an op amp offset voltage of 5 mV will shift the first

LED threshold as much as 4 dB, so that an offset trim may

be required. Note that a single adjustment can null out offset

in both the precision rectifier and the 30 dB gain stage. Alter-

natively, instead of amplifying, input signals of sufficient am-

plitude can be fed directly to the lower LM3915 and attenu-

ated by 30 dB to drive the second LM3915.

A simple, low cost approach to cascading two LM3915s is to

set the reference voltages of the two chips 30 dB apart as in

Figure 5. Potentiometer R1 is used to adjust the full scale

voltage of LM3915 1 to 316 mV nominally while the second

IC’s reference is set at 10V by R4. The drawback of this

method is that the threshold of LED 1 is only 14 mV and,

since the LM3915 can have an offset voltage as high as

10 mV, large errors can occur. This technique is not recom-

mended for 60 dB displays requiring good accuracy at the

first few display thresholds.

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Application Hints (Continued)

DS005104-13

FIGURE 5. Low Cost Circuit for 60 dB Display

DS005104-14

FIGURE 6. Improved Circuit for 60 dB Display

To extend this approach to get a 90 dB display, another

30 dB of amplification must be placed in the signal path

ahead of the lowest LM3915. Extreme care is required as the

lowest LM3915 displays input signals down to 0.5 mV! Sev-

eral offset nulls may be required. High currents should not

share the same path as the low level signal. Also power line

wiring should be kept away from signal lines.

450 µA to flow from pin 7 into the divider which means that

the LED current will be at least 5 mA. R1 will typically be be-

tween 1 kΩ and 2 kΩ. To trim the reference voltage, vary R2.

The circuit in Figure 8 shows how to add a LED intensity con-

trol which can vary LED current from 9 mA to 28 mA. The ref-

erence adjustment has some effect on LED intensity but the

reverse is not true.

TIPS ON REFERENCE VOLTAGE

AND LED CURRENT PROGRAMMING

MULTIPLE LM3915s

Figure 9 shows how to obtain a common reference trim and

intensity control for two LM3915s. The two ICs may be con-

nected in cascade for a 60 dB display or may be handling

separate channels for stereo. This technique can be ex-

tended for larger numbers of LM3915s by varying the values

of R1, R2 and R3 in inverse proportion to the number of de-

vices tied in. The ICs’ internal references track within

100 mV so that worst case error from chip to chip is only

SINGLE LM3915

The equations in Figure 7 illustrate how to choose resistor

values to set reference voltage for the simple case where no

LED intensity adjustment is required. A LED current of 10 mA

to 20 mA generally produces adequate illumination. Having

10V full-scale across the internal voltage divider gives best

accuracy by keeping signal level high relative to the offset

voltage of the internal comparators. However, this causes

0.1 dB for V_REF10V.

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Application Hints (Continued)

DS005104-15

FIGURE 7. Design Equations for Fixed LED Intensity

DS005104-16

10V

28 mA

REF

9 mA

LED

FIGURE 8. Varying LED Intensity

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Application Hints (Continued)

DS005104-17

FIGURE 9. Independent Adjustment of Reference Voltage and LED Intensity for Multiple LM3915s

The scheme in Figure 10 is useful when the reference and

LED intensity must be adjusted independently over a wide

Other Applications

For increased resolution, it’s possible to obtain a display with

range. The R_HIvoltage can be adjusted from 1.2V to 10V

a smooth transition between LEDs. This is accomplished by

with no effect on LED current. Since the internal divider here

varying the reference level at pin 6 by 3 dBp-p as shown in

does not load down the reference, minimum LED current is

Figure 11. The signal can be a triangle, sawtooth or sine

much lower. At the minimum recommended reference load

wave from 60 Hz to 1 kHz. The display can be run in either

of 80 µA, LED current is about 0.8 mA. The resistor values

dot or bar mode.

shown give a LED current range from 1.5 mA to 20 mA.

When an exponentially decaying RC discharge waveform is

applied to pin 5, the LM3915’s outputs will switch at equal in-

At the low end of the intensity adjustment, the voltage drop

across the 510Ω current-sharing resistors is so small that

tervals. This makes a simple timer or sequencer. Each time

chip to chip variation in reference voltage may yield a visible

interval is equal to RC/3. The output may be used to drive

variation in LED intensity. The optional approach shown of

logic, opto-couplers, relays or PNP transistors, for example.

connecting the bottom end of the intensity control pot to a

negative supply overcomes this problem by allowing a larger

voltage drop across the (larger) current-sharing resistors.

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Typical Applications

DS005104-18

Optional circuit for improved intensity matching at low currents.

See text.

FIGURE 10. Wide-Range Adjustment of Reference Voltage and LED Intensity for Multiple LM3915s

DS005104-19

FIGURE 11. 0V to 10V Log Display with Smooth Transitions

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Typical Applications (Continued)

Extended Range VU Meter

DS005104-20

This application shows that the LED supply requires minimal filtering.

†

See Application Hints for optional Peak or Average Detector.

Adjust R3 for 3 dB difference between LED #11 and LED #12.

Vibration Meter

DS005104-21

LED

Threshold

60 mV

80 mV

110 mV

160 mV

220 mV

320 mV

440 mV

630 mV

890 mV

1.25V

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Typical Applications (Continued)

Indicator and Alarm, Full-Scale Changes Display from Dot to Bar

DS005104-22

The input to the dot bar switch may be taken from cathodes of other LEDs.

Display will change to bar as soon as the LED so selected begins to light.

Optional. Shunts 100 µA auxiliary sink current away from LED 1.

60 dB Dot Mode Display

DS005104-23

Optional. Shunts 100 µA auxiliary sink current away from LED 11.

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Typical Applications (Continued)

Driving Vacuum Fluorescent Display

DS005104-24

R7 thru R15: 10k 10%

D1, D2: 1N914 or 1N4148

Half-wave peak detector.

See Application Hints.

Low Current Bar Mode Display

DS005104-25

Supply current drain is only 15 mA with ten LEDs illuminated.

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Typical Applications (Continued)

Driving Liquid Crystal Display

DS005104-26

Bar Display with Alarm Flasher

DS005104-27

Full-scale causes the full bar display to flash. If the junction of R1 and C1 is connected to a different LED cathode, the display will flash when that LED lights,

and at any higher input signal.

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Typical Applications (Continued)

Precision Null Meter

DS005104-28

Logarithmic response allows coarse and fine adjustments without changing scale.

Resolution ranges from 10 mV at V

0 mV to 500 mV at V

1.25V.

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Typical Applications (Continued)

Operating with a High Voltage Supply (Dot Mode Only)

DS005104-29

The LED currents are approximately 10 mA, and the LM3915 outputs operate in saturation for minimum dissipation.

This point is partially regulated and decreases in voltage with temperature. Voltage requirements of the LM3915 also decrease with temperature.

Light Meter

DS005104-30

Resistor value selects exposure

1/2 f/stop resolution

Ten f/stop range (1000:1)

Typical supply current is 8 mA.

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Typical Applications (Continued)

Audio Power Meter

DS005104-31

Load

Impedance

4Ω

8Ω

10k

18k

30k

16Ω

See Application Hints for optional Peak

or Average Detector

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Connection Diagram

Dual-in-Line Package

DS005104-32

Top View

Order Number LM3915N-1

See NS Package Number NA18A

Order Number LM3915N

See NS Package Number N18A

Discontinued, Life Time Buy date 12/20/99

sured at the current source outputs. As the forward voltage

Definition of Terms

of an LED does not change significantly with a small change

in forward current, this is equivalent to changing the voltage

at the LED anodes by the same amount.

Absolute Accuracy: The difference between the observed

threshold voltage and the ideal threshold voltage for each

comparator. Specified and tested with 10V across the inter-

nal voltage divider so that resistor ratio matching error pre-

dominates over comparator offset voltage.

Line Regulation: The average change in reference output

voltage (V_REF) over the specified range of supply voltage

(V⁺).

Adjust Pin Current: Current flowing out of the reference ad-

just pin when the reference amplifier is in the linear region.

Load Regulation: The change in reference output voltage

over the specified range of load current (I_L(REF)).

Comparator Gain: The ratio of the change in output current

(I_LED) to the change in input voltage (V_IN) required to pro-

duce it for a comparator in the linear region.

Offset Voltage: The differential input voltage which must be

applied to each comparator to bias the output in the linear re-

gion. Most significant error when the voltage across the in-

ternal voltage divider is small. Specified and tested with pin

6 voltage (V_RHI) equal to pin 4 voltage (V_RLO).

Dropout Voltage: The voltage measured at the current

source outputs required to make the output current fall by

Relative Accuracy: The difference between any two adja-

cent threshold points. Specified and tested with 10V across

the internal voltage divider so that resistor ratio matching er-

ror predominates over comparator offset voltage.

Input Bias Current: Current flowing out of the signal input

when the input buffer is in the linear region.

LED Current Regulation: The change in output current over

the specified range of LED supply voltage (V_LED) as mea-

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Physical Dimensions inches (millimeters) unless otherwise noted

Note: Unless otherwise specified.

1. Standard Lead Finish:

200 microinches /5.08 micrometer minimum

lead/tin 37/63 or 15/85 on alloy 42 or equivalent or copper

2. Reference JEDEC registration MS-001, Variation AC, dated May 1993.

Molded Dual-In-Line Package (N)

Order Number LM3915N-1

NS Package Number NA18A

www.national.com

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

Molded Dual-In-Line Package (N)

Order Number LM3915N

NS Package Number N18A

Discontinued, Life Time Buy date 12/20/99

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

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

the life support device or system, or to affect its

safety or effectiveness.

National Semiconductor

Corporation

Americas

Tel: 1-800-272-9959

Fax: 1-800-737-7018

Email: support@nsc.com

National Semiconductor

Europe

National Semiconductor

Asia Pacific Customer

Response Group

Tel: 65-2544466

Fax: 65-2504466

National Semiconductor

Japan Ltd.

Tel: 81-3-5639-7560

Fax: 81-3-5639-7507

Fax: +49 (0) 1 80-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 1 80-530 85 85

English Tel: +49 (0) 1 80-532 78 32

Français Tel: +49 (0) 1 80-532 93 58

Italiano Tel: +49 (0) 1 80-534 16 80

Email: sea.support@nsc.com

www.national.com

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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LM3915J产品参数

型号:	LM3915J
是否Rohs认证：	不符合
生命周期：	Obsolete
包装说明：	DIP, DIP18,.3
Reach Compliance Code：	unknown
风险等级：	5.92
其他特性：	BARGRAPH
显示模式：	BAR GRAPH
JESD-30 代码：	R-XDIP-T18
JESD-609代码：	e0
位数/字符：	10-DIGIT
端子数量：	18
最高工作温度：	70 °C
最低工作温度：
封装主体材料：	CERAMIC
封装代码：	DIP
封装等效代码：	DIP18,.3
封装形状：	RECTANGULAR
封装形式：	IN-LINE
认证状态：	Not Qualified
子类别：	Display Drivers
表面贴装：	NO
技术：	BIPOLAR
温度等级：	COMMERCIAL
端子面层：	Tin/Lead (Sn/Pb)
端子形式：	THROUGH-HOLE
端子节距：	2.54 mm
端子位置：	DUAL
Base Number Matches：	1

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