LM3915 Dot/Bar Display Driver - Experimentalists …

1 LM3915 Dot/Bar Display DriverGeneral DescriptionThe LM3915 is a monolithic integrated circuit that sensesanalog voltage levels and drives ten LEDs, LCDs or vacuumfluorescent displays, providing a logarithmic 3 dB/step ana-log Display . One pin changes the Display from a bar graph toa moving dot Display . LED current drive is regulated andprogrammable, eliminating the need for current limiting re-sistors. The whole Display system can operate from a singlesupply as low as 3V or as high as IC contains an adjustable voltage reference and anaccurate ten-step voltage divider. The high-impedance inputbuffer accepts signals down to ground and up to within the positive supply. Further, it needs no protection againstinputs of 35V. The input buffer drives 10 individual com-parators referenced to the precision divider.

2 Accuracy istypically better than 1 LM3915 s 3 dB/step Display is suited for signals withwide dynamic range, such as audio level, power, light inten-sity or vibration. Audio applications include average or peaklevel indicators, power meters and RF signal strengthmeters. Replacing conventional meters with an LED bargraph results in a faster responding, more rugged displaywith high visibility that retains the ease of interpretation of ananalog LM3915 is extremely easy to apply. A full-scalemeter requires only one resistor in addition to the ten more resistor programs the full-scale anywhere to 12V independent of supply voltage. LED brightnessis easily controlled with a single LM3915 is very versatile. The outputs can drive LCDs,vacuum fluorescents and incandescent bulbs as well asLEDs of any color.

3 Multiple devices can be cascaded for adot or bar mode Display with a range of 60 or 90 can also be cascaded with LM3914s for a linear/log Display or with LM3916s for an extended-range dB/step, 30 dB rangenDrives LEDs, LCDs, or vacuum fluorescentsnBar or dot Display mode externally selectable by usernExpandable to displays of 90 dBnInternal voltage reference from to 12 VnOperates with single supply of 3V to 25 VnInputs operate down to groundnOutput current programmable from 1 mA to 30 mAnInput withstands 35V without damage or false outputsnOutputs are current regulated, open collectorsnDirectly drives TTL or CMOSnThe internal 10-step divider is floating and can bereferenced to a wide range of voltagesThe LM3915 is rated for operation from 0 C to +70 C.

4 TheLM3915N-1 is available in an 18-lead molded DIP 2001LM3915 Dot/Bar Display Driver 2001 National Semiconductor Applications0V to 10V Log DisplayDS005104-1 Notes:Capacitor C1 is required if leads to the LED supply are 6" or as shown is wired for dot mode. For bar mode, connect pin 9 to pin 3. VLED must be kept below 7V or dropping resistor should be used to limit IC Maximum Ratings(Note 1)If Military/Aerospace specified devices are required,please contact the National Semiconductor Sales Office/Distributors for availability and Dissipation (Note 6)Molded DIP(N)1365 mWSupply Voltage25 VVoltage on Output Drivers25 VInput Signal Overvoltage (Note 4) 35 VDivider Voltage 100 mV to V+Reference Load Current10 mAStorage Temperature Range 55 C to +150 CLead Temperature(Soldering, 10 sec.)

5 260 CElectrical Characteristics(Notes 2, 4)ParameterConditions(Note 2)MinTypMaxUnitsCOMPARATORO ffset Voltage, Buffer and FirstComparator0V VRLO=VRHI 12V,ILED=1mA310mVOffset Voltage, Buffer and Any OtherComparator0V VRLO=VRHI 12V,ILED=1mA315mVGain ( ILED/ VIN)IL(REF)= 2 mA, ILED= 10 mA38mA/mVInput Bias Current (at Pin 5)0V VIN (V+ )25100nAInput Signal OvervoltageNo Change in Display 3535 VVOLTAGE-DIVIDERD ivider ResistanceTotal, Pin 6 to 4162836k Relative Accuracy (Input ChangeBetween Any Two Threshold Points)(Note 3) Accuracy at Each ThresholdPoint(Note 3)VIN= 3, 6 dB + 9 dB + 12, 15, 18 dB + 21, 24, 27 dB + REFERENCEO utput mA IL(REF) 4 mA,V+=VLED= Regulation3V V+ mA IL(REF) 4 mA,V+=VLED= Voltage Change withTemperature0 C TA +70 C, IL(REF)= 1 mA,V+=VLED=5V1%Adjust Pin Current75120 AOUTPUT DRIVERSLED CurrentV+=VLED= 5V, IL(REF)= 1 mA71013mALED Current Difference (BetweenLargest and Smallest LED Currents)VLED= 5V, ILED=2mAVLED= 5V, ILED20 Current Regulation2V VLED 17V, ILED=2mAILED= VoltageILED(ON)= 20 mA,@VLED= 5V, ILED= VoltageILED= mA, IL(REF)= Leakage, Each Collector(Bar Mode) (Note 5) AOutput LeakagePins 10 18(Dot Mode) (Note 5) APin 160150450 ASUPPLY CURRENTS tandby Supply Current(All Outputs Off)V+= +5V, IL(REF)= mAV+= +20V, IL(REF)= Characteristics(Notes 2, 4) (Continued)Note 1:Absolute Maximum Ratings indicate limits beyond which damage to the device may occur.

6 Operating Ratings indicate conditions for which the device isfunctional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions whichguarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limitis given, however, the typical value is a good indication of device 2:Unless otherwise stated, all specifications apply with the following conditions:3 VDC V+ 20 VDC VRLO 12 VDCTA= 25 C, IL(REF)= mA, pin 9 connected to pin 3 (bar mode).3 VDC VLED V+VREF,VRHI,VRLO (V+ )For higher power dissipations, pulse testing is used. VRHI 12 VDC0V VIN V+ 3:Accuracy is measured referred to 0 dB = + VDCat pin 5, with + VDCat pin 6, and VDCat pin 4.

7 At lower full scale voltages, buffer andcomparator offset voltage may add significant error. See table for threshold 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 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) isdisabled if pin 9 is pulled or more below 6:The maximum junction temperature of the LM3915 is 100 C. Devices must be derated for operation at elevated temperatures. Junction to ambient thermalresistance is 55 C/W for the molded DIP (N package).Threshold Voltage(Note 3)OutputdBMinTypMaxOutputdBMinTypMax1 Performance CharacteristicsSupply Current vs TemperatureDS005104-34 Operating Input Bias Current vsTemperatureDS005104-35 Reference Voltage vsTemperatureDS005104-36 Reference Adjust PinCurrent vs TemperatureDS005104-37 LED Current-RegulationDropoutDS005104-38 LED Driver Performance Characteristics(Continued)Input Current BeyondSignal Range (Pin 5)DS005104-40 LED Current vsReference LoadingDS005104-41 LED Driver CurrentRegulationDS005104-42 Total Divider Resistancevs TemperatureDS005104-43 Common-Mode LimitsDS005104-44 Output Diagram(Showing Simplest Application) DescriptionThe simplified LM3915 block diagram is included to give thegeneral idea of the circuit s operation.

8 A high input imped-ance buffer operates with signals from ground to 12V, and isprotected against reverse and overvoltage signals. The sig-nal is then applied to a series of 10 comparators; each ofwhich is biased to a different comparison level by the the example illustrated, the resistor string is connected tothe internal reference voltage. In this case, for each3 dB that the input signal increases, a comparator will switchon another indicating LED. This resistor divider can be con-nected between any 2 voltages, providing that they are atleast below V+and no lower than V .INTERNAL VOLTAGE REFERENCEThe reference is designed to be adjustable and develops anominal between the REF OUT (pin 7) and REF ADJ(pin 8) terminals. The reference voltage is impressed acrossprogram resistor R1 and, since the voltage is constant, aconstant current I1then flows through the output set resistorR2 giving an output voltage of:Since the 120 A current (max) from the adjust terminalrepresents an error term, the reference was designed tominimize changes of this current with V+and load correct operation, reference load current should be be-tween 80 A and 5 mA.

9 Load capacitance should be lessthan PROGRAMMINGA feature not completely illustrated by the block diagram isthe LED brightness control. The current drawn out of thereference voltage pin (pin 7) determines LED current. Ap-proximately 10 times this current will be drawn through eachlighted LED, and this current will be relatively constant de-spite supply voltage and temperature changes. Currentdrawn by the internal 10-resistor divider, as well as by theexternal current and voltage-setting divider should be in-cluded in calculating LED drive current. The ability to modu-late LED brightness with time, or in proportion to input volt-age and other signals can lead to a number of novel displaysor ways of indicating input overvoltages, alarms, LM3915 outputs are current-limited NPN transistors asshown below.

10 An internal feedback loop regulates the tran-sistor drive. Output current is held at about 10 times thereference load current, independent of output voltage andprocessing variables, as long as the transistor is not may be run in saturation with no adverse effects,making it possible to directly drive logic. The effective satu-ration resistance of the output transistors, equal to REplusthe transistors collector resistance, is about 50 . It s alsopossible to drive LEDs from rectified AC with no filtering. Toavoid oscillations, the LED supply should be bypassed with F tantalum or 10 F aluminum electrolytic PIN USEPin 9, the Mode Select input, permits chaining of multipleLM3915s, and controls bar or dot mode operation. Thefollowing tabulation shows the basic ways of using this more complex uses will be illustrated in the Graph Display :Wire Mode Select (pin 9)directlyto pin3(V+pin).