LM3914 Dot/Bar Display Driver: General Description
LM3914 Dot/Bar Display Driver: General Description
February 2003
  LM3914
  Dot/Bar Display Driver
  General Description                                             Much of the display flexibility derives from the fact that all
                                                                  outputs are individual, DC regulated currents. Various effects
  The LM3914 is a monolithic integrated circuit that senses       can be achieved by modulating these currents. The indi-
  analog voltage levels and drives 10 LEDs, providing a linear    vidual outputs can drive a transistor as well as a LED at the
  analog display. A single pin changes the display from a         same time, so controller functions including “staging” control
  moving dot to a bar graph. Current drive to the LEDs is         can be performed. The LM3914 can also act as a program-
  regulated and programmable, eliminating the need for resis-     mer, or sequencer.
  tors. This feature is one that allows operation of the whole
                                                                  The LM3914 is rated for operation from 0˚C to +70˚C. The
  system from less than 3V.
                                                                  LM3914N-1 is available in an 18-lead molded (N) package.
  The circuit contains its own adjustable reference and accu-
                                                                  The following typical application illustrates adjusting of the
  rate 10-step voltage divider. The low-bias-current input
                                                                  reference to a desired value, and proper grounding for ac-
  buffer accepts signals down to ground, or V−, yet needs no
                                                                  curate operation, and avoiding oscillations.
  protection against inputs of 35V above or below ground. The
  buffer drives 10 individual comparators referenced to the
  precision divider. Indication non-linearity can thus be held    Features
  typically to 1⁄2%, even over a wide temperature range.          n Drives LEDs, LCDs or vacuum fluorescents
  Versatility was designed into the LM3914 so that controller,    n Bar or dot display mode externally selectable by user
  visual alarm, and expanded scale functions are easily added     n Expandable to displays of 100 steps
  on to the display system. The circuit can drive LEDs of many    n Internal voltage reference from 1.2V to 12V
  colors, or low-current incandescent lamps. Many LM3914s         n Operates with single supply of less than 3V
  can be “chained” to form displays of 20 to over 100 seg-        n Inputs operate down to ground
  ments. Both ends of the voltage divider are externally avail-
                                                                  n Output current programmable from 2 mA to 30 mA
  able so that 2 drivers can be made into a zero-center meter.
                                                                  n No multiplex switching or interaction between outputs
  The LM3914 is very easy to apply as an analog meter circuit.
                                                                  n Input withstands ± 35V without damage or false outputs
  A 1.2V full-scale meter requires only 1 resistor and a single
  3V to 15V supply in addition to the 10 display LEDs. If the 1   n LED driver outputs are current regulated,
  resistor is a pot, it becomes the LED brightness control. The     open-collectors
  simplified block diagram illustrates this extremely simple      n Outputs can interface with TTL or CMOS logic
  external circuitry.                                             n The internal 10-step divider is floating and can be
  When in the dot mode, there is a small amount of overlap or       referenced to a wide range of voltages
  “fade” (about 1 mV) between segments. This assures that at
  no time will all LEDs be “OFF”, and thus any ambiguous
  display is avoided. Various novel displays are possible.
00797001
            Note: Grounding method is typical of all uses. The 2.2µF tantalum or 10 µF aluminum electrolytic capacitor is needed if leads to the LED supply are 6" or
            longer.
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                                                                                                                                    LM3914
 Absolute Maximum Ratings (Note 1)                                Storage Temperature Range               −55˚C to +150˚C
 If Military/Aerospace specified devices are required,            Soldering Information
 please contact the National Semiconductor Sales Office/            Dual-In-Line Package
 Distributors for availability and specifications.                    Soldering (10 seconds)                         260˚C
  Power Dissipation (Note 6)                                         Plastic Chip Carrier Package
    Molded DIP (N)                            1365 mW                  Vapor Phase (60 seconds)                      215˚C
  Supply Voltage                                      25V              Infrared (15 seconds)                         220˚C
  Voltage on Output Drivers                           25V         See AN-450 “Surface Mounting Methods and Their Effect
  Input Signal Overvoltage (Note 4)                  ± 35V        on Product Reliability” for other methods of soldering
  Divider Voltage                        −100 mV to V+            surface mount devices.
  Reference Load Current                         10 mA
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LM3914
            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
            functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
            guarantee 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:
                3 VDC ≤ V+ ≤ 20 VDC        VREF, VRHI, VRLO ≤ (V+ − 1.5V)
                3 VDC ≤ VLED ≤ V+   0V ≤ VIN ≤ V+ − 1.5V
                −0.015V ≤ VRLO ≤ 12VDC    TA = +25˚C, IL(REF) = 0.2 mA, VLED = 3.0V, pin 9 connected to pin 3 (Bar Mode).
                −0.015V ≤ VRHI ≤ 12 VDC
            For higher power dissipations, pulse testing is used.
            Note 3: Accuracy is measured referred to +10.000VDC at pin 6, with 0.000 VDC at pin 4. At lower full-scale voltages, buffer and comparator offset voltage may add
            significant error.
            Note 4: Pin 5 input current must be limited to ± 3mA. 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 20mV of V+. Dot mode results when pin 9 is pulled at least 200mV below V+ or left open circuit. LED No. 10 (pin 10
            output current) is disabled if pin 9 is pulled 0.9V or more below VLED.
            Note 6: The maximum junction temperature of the LM3914 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).
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                                                                                                      LM3914
Typical Performance Characteristics
            Supply Current vs                           Operating Input Bias
              Temperature                              Current vs Temperature
00797002 00797020
00797021 00797022
                                    00797023
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LM3914
            Typical Performance Characteristics                     (Continued)
                                                         00797025
                                                                                                             00797026
                                                        00797027
                                                                                                              00797028
                                                                                                             00797030
                                                    00797029
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                                                                                   LM3914
Block Diagram   (Showing Simplest Application)
00797003
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LM3914
            Functional Description                                                MODE PIN USE
                                                                                  Pin 9, the Mode Select input controls chaining of multiple
            The simplifed LM3914 block diagram is to give the general
                                                                                  LM3914s, and controls bar or dot mode operation. The
            idea of the circuit’s operation. A high input impedance buffer
                                                                                  following tabulation shows the basic ways of using this input.
            operates with signals from ground to 12V, and is protected
                                                                                  Other more complex uses will be illustrated in the applica-
            against reverse and overvoltage signals. The signal is then
                                                                                  tions.
            applied to a series of 10 comparators; each of which is
            biased to a different comparison level by the resistor string.        Bar Graph Display: Wire Mode Select (pin 9) directly to pin
                                                                                  3 (V+ pin).
            In the example illustrated, the resistor string is connected to
            the internal 1.25V reference voltage. In this case, for each          Dot Display, Single LM3914 Driver: Leave the Mode Select
            125mV that the input signal increases, a comparator will              pin open circuit.
            switch on another indicating LED. This resistor divider can           Dot Display, 20 or More LEDs: Connect pin 9 of the first
            be connected between any 2 voltages, providing that they              driver in the series (i.e., the one with the lowest input voltage
            are 1.5V below V+ and no less than V−. If an expanded scale           comparison points) to pin 1 of the next higher LM3914 driver.
            meter display is desired, the total divider voltage can be as         Continue connecting pin 9 of lower input drivers to pin 1 of
            little as 200mV. Expanded-scale meter displays are more               higher input drivers for 30, 40, or more LED displays. The
            accurate and the segments light uniformly only if bar mode is         last LM3914 driver in the chain will have pin 9 wired to pin 11.
            used. At 50mV or more per step, dot mode is usable.                   All previous drivers should have a 20k resistor in parallel with
                                                                                  LED No. 9 (pin 11 to VLED).
            INTERNAL VOLTAGE REFERENCE
            The reference is designed to be adjustable and develops a             Mode Pin Functional Description
            nominal 1.25V between the REF OUT (pin 7) and REF ADJ
                                                                                  This pin actually performs two functions. Refer to the simpli-
            (pin 8) terminals. The reference voltage is impressed across
                                                                                  fied block diagram below.
            program resistor R1 and, since the voltage is constant, a
            constant current I1 then flows through the output set resistor                  Block Diagram of Mode Pin Description
            R2 giving an output voltage of:
00797004
                                                                                                                                          00797005
            Since the 120µA current (max) from the adjust terminal                *High for bar
            represents an error term, the reference was designed to
            minimize changes of this current with V+ and load changes.
                                                                                  DOT OR BAR MODE SELECTION
            CURRENT PROGRAMMING                                                   The voltage at pin 9 is sensed by comparator C1, nominally
            A feature not completely illustrated by the block diagram is          referenced to (V+ − 100mV). The chip is in bar mode when
            the LED brightness control. The current drawn out of the              pin 9 is above this level; otherwise it’s in dot mode. The
            reference voltage pin (pin 7) determines LED current. Ap-             comparator is designed so that pin 9 can be left open circuit
            proximately 10 times this current will be drawn through each          for dot mode.
            lighted LED, and this current will be relatively constant de-         Taking into account comparator gain and variation in the
            spite supply voltage and temperature changes. Current                 100mV reference level, pin 9 should be no more than 20mV
            drawn by the internal 10-resistor divider, as well as by the          below V+ for bar mode and more than 200mV below V+ (or
            external current and voltage-setting divider should be in-            open circuit) for dot mode. In most applications, pin 9 is
            cluded in calculating LED drive current. The ability to modu-         either open (dot mode) or tied to V+ (bar mode). In bar mode,
            late LED brightness with time, or in proportion to input volt-        pin 9 should be connected directly to pin 3. Large currents
            age and other signals can lead to a number of novel displays          drawn from the power supply (LED current, for example)
            or ways of indicating input overvoltages, alarms, etc.                should not share this path so that large IR drops are avoided.
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                                                                                                                                          LM3914
Mode Pin Functional Description                                     OTHER DEVICE CHARACTERISTICS
 (Continued)                                                        The LM3914 is relatively low-powered itself, and since any
                                                                    number of LEDs can be powered from about 3V, it is a very
DOT MODE CARRY                                                      efficient display driver. Typical standby supply current (all
In order for the display to make sense when multiple                LEDs OFF) is 1.6mA (2.5mA max). However, any reference
LM3914s are cascaded in dot mode, special circuitry has             loading adds 4 times that current drain to the V+ (pin 3)
been included to shut off LED No. 10 of the first device when       supply input. For example, an LM3914 with a 1mA reference
LED No. 1 of the second device comes on. The connection             pin load (1.3k), would supply almost 10mA to every LED
for cascading in dot mode has already been described and is         while drawing only 10mA from its V+ pin supply. At full-scale,
depicted below.                                                     the IC is typically drawing less than 10% of the current
As long as the input signal voltage is below the threshold of       supplied to the display.
the second LM3914, LED No. 11 is off. Pin 9 of LM3914               The display driver does not have built-in hysteresis so that
No. 1 thus sees effectively an open circuit so the chip is in       the display does not jump instantly from one LED to the next.
dot mode. As soon as the input voltage reaches the thresh-          Under rapidly changing signal conditions, this cuts down
old of LED No. 11, pin 9 of LM3914 No. 1 is pulled an LED           high frequency noise and often an annoying flicker. An “over-
drop (1.5V or more) below VLED. This condition is sensed by         lap” is built in so that at no time between segments are all
comparator C2, referenced 600mV below VLED. This forces             LEDs completely OFF in the dot mode. Generally 1 LED
the output of C2 low, which shuts off output transistor Q2,         fades in while the other fades out over a mV or more of
extinguishing LED No. 10.                                           range (Note 3). The change may be much more rapid be-
VLED is sensed via the 20k resistor connected to pin 11. The        tween LED No. 10 of one device and LED No. 1 of a second
very small current (less than 100µA) that is diverted from          device “chained” to the first.
LED No. 9 does not noticeably affect its intensity.                 The LM3914 features individually current regulated LED
An auxiliary current source at pin 1 keeps at least 100µA           driver transistors. Further internal circuitry detects when any
flowing through LED No. 11 even if the input voltage rises          driver transistor goes into saturation, and prevents other
high enough to extinguish the LED. This ensures that pin 9 of       circuitry from drawing excess current. This results in the
LM3914 No. 1 is held low enough to force LED No. 10 off             ability of the LM3914 to drive and regulate LEDs powered
when any higher LED is illuminated. While 100µA does not            from a pulsating DC power source, i.e., largely unfiltered.
normally produce significant LED illumination, it may be            (Due to possible oscillations at low voltages a nominal by-
noticeable when using high-efficiency LEDs in a dark envi-          pass capacitor consisting of a 2.2µF solid tantalum con-
ronment. If this is bothersome, the simple cure is to shunt         nected from the pulsating LED supply to pin 2 of the LM3914
LED No. 11 with a 10k resistor. The 1V IR drop is more than         is recommended.) This ability to operate with low or fluctu-
the 900mV worst case required to hold off LED No. 10 yet            ating voltages also allows the display driver to interface with
small enough that LED No. 11 does not conduct significantly.        logic circuitry, opto-coupled solid-state relays, and low-
                                                                    current incandescent lamps.
00797006
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LM3914
            Typical Applications
                                   Zero-Center Meter, 20-Segment
00797007
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                                                                                                                                                                     LM3914
Typical Applications                             (Continued)
                                                                                                                                           00797008
*This application illustrates that the LED supply needs practically no filtering
Calibration: With a precision meter between pins 4 and 6 adjust R1 for voltage VD of 1.20V. Apply 4.94V to pin 5, and adjust R4 until LED No. 5 just lights.
The adjustments are non-interacting.
                                                                    Application Example:
                                                                    Grading 5V Regulators
                                                            Highest No.
                                                                                    Color   VOUT(MIN)
                                                              LED on
                                                                   10              Red        5.54
                                                                    9              Red        5.42
                                                                    8              Yellow     5.30
                                                                    7              Green      5.18
                                                                    6              Green      5.06
                                                                                     5V
                                                                    5              Green      4.94
                                                                    4              Green      4.82
                                                                    3              Yellow      4.7
                                                                    2              Red        4.58
                                                                    1              Red        4.46
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LM3914
            Typical Applications                           (Continued)
                                                                                                                                           00797009
            LEDs light up as illustrated with the upper lit LED indicating the actual input voltage. The display appears to increase resolution and provides an analog
            indication of overrange.
                                                                                                                                                      00797010
            *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.
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                                                                                                                                                                          LM3914
Typical Applications                            (Continued)
                                                                                                                                   00797011
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.
                                                                                                                                   00797012
Hysteresis is 0.5 mV to 1 mV
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LM3914
            Typical Applications                          (Continued)
                                                                                                                              00797013
            The LED currents are approximately 10mA, and the LM3914 outputs operate in saturation for minimum dissipation.
            *This point is partially regulated and decreases in voltage with temperature. Voltage requirements of the LM3914 also decrease with temperature.
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                                                                                                                                                                    LM3914
Typical Applications                          (Continued)
                                                                                                                               00797014
*The exact wiring arrangement of this schematic shows the need for Mode Select (pin 9) to sense the V+ voltage exactly as it appears on pin 3.
Programs LEDs to 10mA
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LM3914
            Application Hints                (Continued)                            Non-Interacting Adjustments For Expanded Scale
                                                                                    Meter (4.5V to 5V, Bar or Dot Mode)
            APPLICATION TIPS FOR THE LM3914 ADJUSTABLE                              This arrangement allows independent adjustment of LED
            REFERENCE                                                               brightness regardless of meter span and zero adjustments.
                                                                                    First, V1 is adjusted to 5V, using R2. Then the span (voltage
            Greatly Expanded Scale (Bar Mode Only)
                                                                                    across R4) can be adjusted to exactly 0.5V using R6 without
            Placing the LM3914 internal resistor divider in parallel with a         affecting the previous adjustment.
            section (.230Ω) of a stable, low resistance divider greatly
                                                                                    R9 programs LED currents within a range of 2.2mA to 20mA
            reduces voltage changes due to IC resistor value changes
                                                                                    after the above settings are made.
            with temperature. Voltage V1 should be trimmed to 1.1V first
            by use of R2. Then the voltage V2 across the IC divider string
            can be adjusted to 200mV, using R5 without affecting V1.
            LED current will be approximately 10mA.
00797015
            Adjusting Linearity Of Several Stacked                                  The references associated with LM3914s No. 1 and No. 2
            dividers                                                                should have their Ref Adj pins (pin 8) wired to ground, and
            Three internal voltage dividers are shown connected in se-              their Ref Outputs loaded by a 620Ω resistor to ground. This
            ries to provide a 30-step display. If the resulting analog meter        makes available similar 20mA current outputs to all the LEDs
            is to be accurate and linear the voltage on each divider must           in the system.
            be adjusted, preferably without affecting any other adjust-             If an independent LED brightness control is desired (as in
            ments. To do this, adjust R2 first, so that the voltage across          the previous application), a unity gain buffer, such as the
            R5 is exactly 1V. Then the voltages across R3 and R4 can                LM310, should be placed between pin 7 and R1, similar to
            be independently adjusted by shunting each with selected                the previous application.
            resistors of 6kΩ or higher resistance. This is possible be-
            cause the reference of LM3914 No. 3 is acting as a constant
            current source.
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                                                                                                                                      LM3914
Application Hints               (Continued)
Non-Interacting Adjustments for Expanded Scale Meter (4.5V to 5V, Bar or Dot Mode)
00797016
00797017
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LM3914
            Connection Diagrams
                                         Plastic Chip Carrier Package
                                                                           00797018
                                                  Top View
                                           Order Number LM3914V
                                        See NS Package Number V20A
Dual-in-Line Package
                                                                                00797019
                                                   Top View
                                           Order Number LM3914N-1
                                        See NS Package Number NA18A
                                           Order Number LM3914N *
                                         See NS Package Number N18A
                                  * Discontinued, Life Time Buy date 12/20/99
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                                                                                                                                           LM3914
LM3914 MDC MWC Dot/Bar Display Driver
                                                                                 00797035
                                                       Die Layout (D - Step)
Die/Wafer Characteristics
                      Fabrication Attributes                                                 General Die Information
Physical Die Identification                        3914                    Bond Pad Opening Size (min)             94µm x 105µm
Die Step                                           D                       Bond Pad Metalization                   ALUMINUM
                        Physical Attributes                                Passivation                             VOM NITRIDE
Wafer Diameter                                     150mm                   Back Side Metal                         Bare Back
Dise Size (Drawn)                                  2591µm x 2438µm         Back Side Connection                    Floating
                                                   102.0mils x
                                                   96.0mils
Thickness                                          330µm Nominal
Min Pitch                                          175µm Nominal
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LM3914
            Die/Wafer Characteristics     (Continued)
                             IN U.S.A
                             Tel #:               1 877 Dial Die 1 877 342 5343
                             Fax:                 1 207 541 6140
                             IN EUROPE
                             Tel:                 49 (0) 8141 351492 / 1495
                             Fax:                 49 (0) 8141 351470
                             IN ASIA PACIFIC
                             Tel:                 (852) 27371701
                             IN JAPAN
                             Tel:                 81 043 299 2308
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                                                                                                                LM3914
Physical Dimensions                            inches (millimeters)
unless otherwise noted
                                                                           21                www.national.com
LM3914 Dot/Bar Display Driver
                                Physical Dimensions                      inches (millimeters) unless otherwise noted (Continued)
                                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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