TI1 LM3916N-1/NOPB Lm3916 dot/bar display driver Datasheet

LM3916
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LM3916 Dot/Bar Display Driver
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FEATURES
DESCRIPTION
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•
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The LM3916 is a monolithic integrated circuit that
senses analog voltage levels and drives ten LEDs,
LCDs or vacuum fluorescent displays, providing an
electronic version of the popular VU meter. One pin
changes the display from a bar graph to a moving dot
display. LED current drive is regulated and
programmable, eliminating the need for current
limiting resistors. The whole display system can
operate from a single supply as low as 3V or as high
as 25V.
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2
•
•
•
•
•
•
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•
•
Fast Responding Electronic VU Meter
Drivers LEDs, LCDs, or Vacuum Fluorescents
Bar or Dot Display Mode Externally Selectable
by User
Expandable to Displays of 70 dB
Internal Voltage Reference from 1.2V to 12V
Operates with Single Supply of 3V to 25V
Inputs Operate Down to Ground
Output Current Programmable from 1 mA to 30
mA
Input Withstands ±35V without Damage or
False Outputs
Outputs are Current Regulated, Open
Collectors
Directly Drives TTL or CMOS
The Internal 10-step Divider is Floating and
can be Referenced to a Wide Range of
Voltages
The LM3916 is Rated for Operation from 0°C to
+70°C. The LM3916N-1 is Available in an 18lead PDIP Package.
The IC contains an adjustable voltage reference and
an accurate ten-step voltage divider. The highimpedance 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 comparators
referenced to the precision divider. Accuracy is
typically better than 0.2 dB.
Audio applications include average or peak level
indicators, and power 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.
The LM3916 is extremely easy to apply. A 1.2V fullscale meter requires only one resistor in addition to
the ten LEDs. One more resistor programs the fullscale anywhere from 1.2V to 12V independent of
supply voltage. LED brightness is easily controlled
with a single pot.
The LM3916 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 for increased
range and/or resolution. Useful in other applications
are the linear LM3914 and the logarithmic LM3915.
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
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Typical Applications
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. VLED must be kept below 7V or dropping
resistor should be used to limit IC power dissipation.
Figure 1. 0V to 10V VU Meter
2
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
ABSOLUTE MAXIMUM RATINGS (1) (2)
Power Dissipation
(3)
PDIP (NFK)
1365 mW
Supply Voltage
25V
Voltage on Output Drivers
Input Signal Overvoltage
25V
(4)
±35V
−100 mV to V+
Divider Voltage
Reference Load Current
10 mA
−55°C to +150°C
Storage Temperature Range
Lead Temperature
(Soldering, 10 seconds)
(1)
(2)
(3)
(4)
260°C
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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not specified for parameters where no limit is given, however, the typical value is a good indication
of device performance.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
The maximum junction temperature of the LM3916 is 100°C. Devices must be derated for operation at elevated temperatures. Junction
to ambient thermal resistance is 55°C/W for the PDIP (NFK package).
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.
ELECTRICAL CHARACTERISTICS (1) (2)
Parameter
Conditions
(1)
Min
Typ
Max
Units
COMPARATORS
Offset Voltage, Buffer and First Comparator
0V ≤ VRLO = VRHI ≤ 12V,
ILED = 1 mA
3
10
mV
Offset Voltage, Buffer and Any Other Comparator
0V ≤ VRLO = VRHI ≤ 12V,
ILED = 1 mA
3
15
mV
Gain (ΔILED/ ΔVIN)
I(REF) = 2 mA, ILED = 10 mA
Input Bias Current (at Pin 5)
0V ≤ VIN ≤ (V+ −1.5V)
Input Signal Overvoltage
No Change in Display
3
8
25
−35
mA/mV
100
nA
35
V
VOLTAGE DIVIDER
Divider Resistance
Total, Pin 6 to 4
Relative Accuracy (Input Change
Between Any Two Threshold Points)
(3)
Absolute Accuracy
−1 dB ≤ VIN ≤ 3 dB
−7 dB ≤ VIN ≤ −1 dB
−10 dB ≤ VIN ≤ −7 dB
8
12
17
kΩ
0.75
1.5
2.5
1.0
2.0
3.0
1.25
2.5
2.5
dB
dB
dB
+0.25
+0.5
+1
dB
dB
dB
1.28
1.34
V
(3)
VIN = 2, 1, 0, −1 dB
VIN = −3, −5 dB
VIN = −7, −10, −20 dB
−0.25
−0.5
−1
VOLTAGE REFERENCE
Output Voltage
0.1 mA ≤ IL(REF) ≤ 4 mA,
V+ = VLED = 5Vg
+
1.2
Line Regulation
3V ≤ V ≤ 18V
0.01
0.03
%/V
Load Regulation
0.1 mA ≤ IL(REF) ≤ 4 mA,
V+ = VLED = 5V
0.4
2
%
(1)
(2)
(3)
Unless otherwise stated, all specifications apply with the following conditions:
3 VDC ≤ V+ ≤ 20 VDC
−0.015V ≤ VRLO ≤ 12 VDC
TA = 25°C, IL(REF) = 0.2 mA, pin 9 connected to pin 3 (bar mode).
3 VDC ≤ VLED ≤ V+
VREF, VRHI, VRLO ≤ (V+ − 1.5V)
For higher power dissipations, pulse testing is used.
−0.015V ≤ VRHI ≤ 12 VDC
0V ≤ VIN ≤ V+ − 1.5V
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.
Accuracy is measured referred to +3 dB = +10.000 VDC at pin 5, with +10.000 VDC at pin 6, and 0.000 VDC at pin 4. At lower full-scale
voltages, buffer and comparator offset voltage may add significant error. See Threshold Voltage.
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ELECTRICAL CHARACTERISTICS(1)(2) (continued)
Parameter
Conditions
(1)
Min
0°C ≤ TA ≤ +70°C, IL(REF) = 1 mA,
V+ = VLED = 5V
Output Voltage Change with Temperature
Typ
Max
1
Adjust Pin Current
75
Units
%
120
μA
OUTPUT DRIVERS
LED Current
V+ = VLED = 5V, IL(REF) = 1 mA
10
13
mA
LED Current Difference (Between Largest and Smallest
LED Currents)
VLED = 5V, ILED = 2 mA
VLED = 5V, ILED = 20 mA
0.12
1.2
0.4
3
mA
mA
LED Current Regulation
2V ≤ VLED ≤ 17V
ILED 2 mA
ILED = 20 mA
0.1
1
0.25
3
mA
mA
1.5
V
0.15
0.4
V
0.1
100
μA
7
Dropout Voltage
ILED(ON) = 20 mA @ VLED = 5V,
ΔILED = 2 mA
Saturation Voltage
ILED = 2.0 mA, IL(REF) = 0.4 mA
Output Leakage, Each Collector
Bar Mode
(4)
Output Leakage
Dot Mode
(4)
Pins 10–18
Pin 1
60
0.1
100
μA
150
450
μA
2.4
6.1
4.2
9.2
mA
mA
SUPPLY CURRENT
V+ = + 5V, IL(REF) = 0.2 mA
V+ = + 20V, IL(REF) = 1.0 mA
Standby Supply Current
(All Outputs Off)
(4)
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 disabled if pin 9 is pulled 0.9V or more below VLED.
LM3916 THRESHOLD VOLTAGE (1)
dB
(1)
4
Volts
Min
Typ
Max
3
9.985
10.000
10.015
2±¼
8.660
8.913
1±¼
7.718
7.943
0±¼
6.879
−1 ± ½
5.957
dB
Volts
Min
Typ
Max
−3 ± ½
4.732
5.012
5.309
9.173
−5 ± ½
3.548
3.981
4.467
8.175
−7 ± 1
2.818
3.162
3.548
7.079
7.286
−10 ± 1
1.995
2.239
2.512
6.310
6.683
−20 ± 1
0.631
0.708
0.794
Accuracy is measured referred to +3 dB = +10.000 VDC at pin 5, with +10.000 VDC at pin 6, and 0.000 VDC at pin 4. At lower full-scale
voltages, buffer and comparator offset voltage may add significant error. See Threshold Voltage.
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TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs
Temperature
Operating Input Bias Current
vs
Temperature
Figure 2.
Figure 3.
Reference Voltage vs
Temperature
Reference Adjust Pin Current
vs
Temperature
Figure 4.
Figure 5.
LED Current-Regulation
Dropout
LED Driver Saturation
Voltage
Figure 6.
Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
6
Input Current Beyond
Signal Range (Pin 5)
LED Current vs
Referenced Loading
Figure 8.
Figure 9.
LED Driver Current
Regulation
Total Divider Resistance
vs Temperature
Figure 10.
Figure 11.
Common-Mode Limits
Output Characteristics
Figure 12.
Figure 13.
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BLOCK DIAGRAM
(Showing Simplest Application)
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FUNCTIONAL DESCRIPTION
The simplified LM3916 block diagram is included to give the general idea of the circuit's operation. A high input
impedance buffer operates with signals from ground to 12V, and is protected against reverse and overvoltage
signals. The signal 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. As the input
voltage varies from 0 to 1.25, the comparator outputs are driven low one by one, switching on the LED indicators.
The resistor divider can be connected between any 2 voltages, providing that they are at least 1.5V below V+ and
no lower than V−.
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 I1 then flows through the output set resistor R2 giving an output voltage of:
Since the 120 μA current (max) from the adjust terminal represents an error term, the reference was designed to
minimize 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.
CURRENT PROGRAMMING
A feature not completely illustrated by the block diagram is the LED brightness control. The current drawn out of
the reference voltage pin (pin 7) determines LED current. Approximately 10 times this current will be drawn
through each lighted LED, and this current will be relatively constant despite supply voltage and temperature
changes. Current drawn by the internal 10-resistor divider, as well as by the external 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 LM3916 outputs are current-limited NPN transistors as shown below. An internal feedback loop regulates
the transistor drive. Output current is held at about 10 times the reference load current, independent of output
voltage and processing variables, as long as the transistor is not saturated.
8
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Figure 14. LM3916 Output Circuit
Outputs may be run in saturation with no adverse effects, making it possible to directly drive logic. The effective
saturation resistance of the output transistors, equal to RE plus the transistors' collector resistance, is about 50Ω.
It's also possible 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.
MODE PIN USE
Pin 9, the Mode Select input, permits chaining of multiple devices, and controls bar or dot mode operation. The
following tabulation shows the basic ways of using this input. Other more complex uses will be illustrated in the
applications.
Bar Graph Display: Wire Mode Select (pin 9) directly to pin 3 (V+ pin).
Dot Display, Single LM3916 Driver: Leave the Mode Select pin open circuit.
Dot Display, 20 or More LEDs: Connect pin 9 of the first drivers in the series (i.e., the one with the lowest input
voltage comparison points) to pin 1 of the next higher LM3916 driver. Continue connecting pin 9 of lower input
drivers to pin 1 of higher input drivers for 30 or more LED displays. The last LM3916 driver in the chain will have
pin 9 left open. All previous drivers should have a 20k resistor in parallel with LED #9 (pin 11 to VLED).
Mode Pin Functional Description
This pin actually performs two functions. Refer to the simplified block diagram below.
*High for bar
Figure 15. Block Diagram of Mode Pin Function
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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 comparator is designed so that pin 9 can be left
open circuit for dot mode.
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 either 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.
DOT MODE CARRY
In order for display to make sense when multiple drivers are cascaded in dot mode, special circuitry has been
included to shut off LED #10 of the first device when LED #1 of the second device comes on. The connection for
cascading in dot mode has already been described and is depicted in Figure 16.
As long as the input signal voltage is below the threshold of the second driver, LED #11 is off. Pin 9 of driver #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, pin 9 of driver #1 is pulled an LED drop (1.5V or more) below VLED. This condition is
sensed by comparator C2, referenced 600 mV below VLED. This forces the output of C2 low, which shuts off
output transistor Q2, extinguishing LED #10.
VLED is sensed via the 20k resistor connected to pin 11. The very small current (less than 100 μA) that is diverted
from 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 driver #1 is held low enough to force LED #10 off
when any higher LED is illuminated. While 100 μA does not normally produce significant LED illumination, it may
be noticeable when using high-efficiency LEDs in a dark environment. If this is bothersome, the simple cure is to
shunt LED #11 (and LED #1) with a 10k resistor. The 1V 1R 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.
In some circuits a number of outputs on the higher device are not used. Examples include the high resolution VU
meter and the expanded range VU meter circuits (see Typical Applications). To provide the proper carry sense
voltage in dot mode, the LEDs of the higher driver IC are tied to VLED through two series-connected diodes as
shown in Figure 17. Shunting the diodes with a 1k resistor provides a path for driver leakage current.
Figure 16. Cascading LM3914/15/16 Series in Dot Mode
10
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Figure 17. Cascading Drivers in Dot Mode with Pin 1 of Driver #2 Unused
OTHER DEVICE CHARACTERISTICS
The LM3915 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 LM3915 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 drawing less than 10% of the current supplied to the display.
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 “overlap” is built in so that at no time are all segments completely off the dot mode. Generally one LED
fades in while the other fades out over a 1 mV range. The change may be much more rapid between LED #10 of
one device and LED #1 of a second device cascaded.
Application Hints
The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode.
These currents flowing out of the ground pin cause voltage drops in external wiring, and thus errors and
oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string to a
single point very near pin 2 is the best solution.
Long wires from VLED to LED anode common can cause oscillations. The usual cure is bypassing the LED
anodes with a 2.2 μF tantalum or 10 μF aluminum electrolytic capacitor. If the LED anode line wiring is
inaccessible, often a 0.1 μF capacitor from pin 1 to pin 2 will be sufficient.
If there is a large amount of LED overlap in the bar mode, oscillation or excessive noise is usually the problem.
In cases where proper wiring and bypassing fail to stop oscillations, V+ voltage at pin 3 is usually below
suggested limits. When several LEDs are lit in dot mode, the problem is usually an AC component of the input
signal which should be filtered out. Expanded scale meter applications may have one or both ends of the internal
voltage divider terminated at relatively high value resistors. These high-impedance ends should be bypassed to
pin 2 with 0.1 μF.
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 or 10 μF aluminum electrolytic capacitor to pin 2.
TIPS ON RECTIFIER CIRCUITS
The simplest way to display an AC signal using the LM3916 is to apply it right to pin 5 unrectified. Since the LED
illuminated represents the instantaneous value of the AC waveform, one can readily discern both peak and
average values of audio signals in this manner. The LM3916 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). A smear or bar
type display results even though the LM3916 is connected for dot mode. The LEDs should be run at 20 mA to 30
mA for high enough average intensity.
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True average or peak detection requires rectification. If an LM3916 is set up with 10V full scale across its voltage
divider, 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 detector in Figure 18 uses a PNP emitterfollower in front of the diode. Now, the transistor's base-emitter voltage cancels out the diode offset, within about
100 mV. This approach is usually satisfactory when a single LM3916 is used for a 23 dB display.
Display circuits such as the extended range VU meter using two or more drivers for a dynamic range of 40 dB or
greater require more accurate detection. In the precision half-wave rectifier of Figure 19 the effective diode 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 detector. The circuit has a gain equal to R2/R1.
It's best to capacitively couple the input. Audio sources frequently have a small DC offset that can cause
significant error 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 adjusted for the correct
output when a low-level AC signal (10 to 20 mV) is applied, rather than adjusting for zero output with zero input.
*DC Couple
Figure 18. Half-Wave Peak Detector
D1, D2: 1N914 or 1N4148
Average
Peak
R2
1k
100k
R3
100k
1k
R1 = R2 for AV = 1
R1 = R2/10 for AV = 10
C1 = 10/R1
Figure 19. Precision Half-Wave Rectifier
12
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For precision full-wave averaging use the circuit in Figure 20. Using 1% resistors for R1 through R4, gain for
positive and negative signal differs by only 0.5 dB worst case. Substituting 5% resistors increases this to 2 dB
worst case. (A 2 dB gain difference means that the display may have a ±1 dB error when the input is a
nonsymmetrical transient). The averaging time constant is R5•C2. A simple modification results in the precision
full-wave detector of Figure 21. Since the filter capacitor is not buffered, this circuit can drive only high
impedance loads such as the input of an LM3916.
D1, D2: 1N914 or 1N4148
Figure 20. Precision Full-Wave Average Detector
D1, D2, D3, D4: 1N914 OR 1N4148
Attack and decay time to DIN PPM spec. Response down 1 dB for 10 ms tone burst. Decays 20 dB in 1.5s.
Figure 21. Precision Full-Wave Peak Detector
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AUDIO METER STANDARDS
VU Meter
The audio level meter most frequently encountered is the VU meter. Its characteristics are defined as the ANSI
specification C165. The LM3916's outputs correspond to the meter indications specified with the omission of the
−2 VU indication. The VU scale divisions differ slightly from a linear scale in order to obtain whole numbers in dB.
Some of the most important specifications for an AC meter are its dynamic characteristics. These define how the
meter responds to transients and how fast the reading decays. The VU meter is a relatively slow full-wave
averaging type, specified to reach 99% deflection in 300 ms and overshoot by 1 to 1.5%. In engineering terms
this means a slightly underdamped second order response with a resonant frequency of 2.1 Hz and a Q of 0.62.
Figure 22 depicts a simple rectifier/filter circuit that meets these criteria.
Design Equations
GAIN
R5
R6
C2
C3
1
100k
43k
2.0
0.56 μF
10
1M
100k
1.0
0.056 μF
Figure 22. Full-Wave Average Detector to VU Meter Specifications*
Peak Program Meter
The VU meter, originally intended for signals sent via telephone lines, has shortcomings when used in high
fidelity systems. Due to its slow response time, a VU meter will not accurately display transients that can saturate
a magnetic tape or drive an amplifier into clipping. The fast-attack peak program meter (PPM) which does not
have this problem is becoming increasingly popular.
While several European organizations have specifications for peak program meters, the German DIN
specification 45406 is becoming a de facto standard. Rather than respond instantaneously to peak, however,
PPM specifications require a finite “integration time” so that only peaks wide enough to be audible are displayed.
DIN 45406 calls for a response of 1 dB down from steady-state for a 10 ms tone burst and 4 dB down for a 3 ms
tone burst. These requirements are consistent with the other frequently encountered spec of 2 dB down for a 5
ms burst and are met by an attack time constant of 1.7 ms.
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The specified return time of 1.5s to −20 dB requires a 650 ms decay time constant. The full-wave peak detector
of Figure 21 satisfies both the attack and decay time criteria.
Cascading The LM3916
The LM3916 by itself covers the 23 dB range of the conventional VU meter. To display signals of 40 dB or 70 dB
dynamic range, the LM3916 may be cascaded with the 3 dB/step LM3915s. Alternatively, two LM3916s may be
cascaded for increased resolution over a 28 dB range. Refer to the Extended Range VU Meter and High
Resolution VU Meter in the Typical Applications section for the complete circuits for both dot and bar mode
displays.
To obtain a display that makes sense when an LM3915 and an LM3916 are cascaded, the −20 dB output from
the LM3916 is dropped. The full-scale display for the LM3915 is set at 3 dB below the LM3916's −10 dB output
and the rest of the thresholds continue the 3 dB/step spacing. A simple, low cost approach is to set the reference
voltage of the two chips 16 dB apart as in Figure 20. The LM3915, with pin 8 grounded, runs at 1.25V full-scale.
R1 and R2 set the LM3916's reference 16 dB higher or 7.89V. Variation in the two on-chip references and
resistor tolerance may cause a ±1 dB error in the −10 dB to −13 dB transition. If this is objectionable, R2 can be
trimmed.
The drawback of the aforementioned approach is that the threshold of LED #1 on the LM3915 is only 56 mV.
Since comparator offset voltage may be as high as 10 mV, large errors can occur at the first few thresholds. A
better approach, as shown in Figure 24, is to keep the reference the same for both drivers (10V in the example)
and amplify the input signal by 16 dB ahead of the LM3915. Alternatively, instead of amplifying, input signals of
sufficient amplitude can be fed directly to the LM3916 and attenuated by 16 dB to drive the LM3915.
VREF2 ≃ 7.89V
Figure 23. Low Cost Circuit for 40 dB Display
(1)
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Figure 24. Improved Circuit for 40 dB Display
(2)
To extend this approach to get a 70 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 2
mV! Several 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.
TIPS ON REFERENCE VOLTAGE AND LED CURRENT PROGRAMMING
Single Driver
The equations in Figure 25 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 1 mA to flow from pin 7 into
the divider which means that the LED current will be at least 10 mA. R1 will typically be between 1 kΩ and 5 kΩ.
To trim the reference voltage, vary R2.
The current in Figure 26 shows how to add a LED intensity control which can vary LED current from 5 mA to 28
mA. Choosing VREF = 5V lowers the current drawn by the ladder, increasing the intensity adjustment range. The
reference adjustment has some effect on LED intensity but the reverse is not true.
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Figure 25. Design Equations for Fixed LED Intensity
5 mA ≤ ILED ≤ 28 mA @ VREF = 5V
Figure 26. Varying LED Intensity
Multiple Drivers
Figure 27 shows how to obtain a common reference trim and intensity control for two drivers. The two ICs may
be connected in cascade or may be handling separate channels for stereo. This technique can be extended for
larger numbers of drivers by varying the values of R1, R2 and R3. Because the LM3915 has a greater ladder
resistance, R5 was picked less than R7 in such a way as to provide equal reference load currents. The ICs'
internal references track within 100 mV so that worst case error from chip to chip is only 0.2 dB for VREF = 5V.
The scheme in Figure 28 is useful when the reference and LED intensity must be adjusted independently over a
wide range. The RHI voltage can be adjusted from 1.2V to 10V with no effect on LED current. Since the internal
divider here does not load down the reference, minimum LED current is much lower. At the minimum
recommended reference load of 80 μA, LED current is about 0.8 mA. The resistor values shown give a LED
current range from 1.5 mA to 25 mA.
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At the low end of the intensity adjustment, the voltage drop across the 510Ω current-sharing resistors is so small
that chip to chip variation in reference voltage may yield a visible variation in LED intensity. The optional
approach shown of 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.
5 mA ≤ ILED ≤ 28 mA
VREF = 5V
Figure 27. Independent Adjustment of Reference Voltage and LED Intensity for Multiple Drivers
1.25V ≤ VREF ≤ 10V
1.5 mA ≤ ILED ≤ 25 mA
Optional circuit for improved intensity matching at low currents. See text.
Figure 28. Wide-Range Adjustment of Reference Voltage and LED intensity for Multiple Drivers
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Other Applications
For increased resolution, it's possible to obtain a display with a smooth transition between LEDs. This is
accomplished by superimposing an AC waveform on top of the input level as shown in Figure 29. The signal can
be a triangle, sawtooth or sine wave from 60 Hz to 1 kHz. The display can be run in either dot or bar mode.
Figure 29. 0V to 10V VU Meter with Smooth Transitions
Typical Applications
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
Figure 30. Extended Range VU Meter (Dot Mode)
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D1, D2: 1N914 or 1N4148
*OPTIONAL SHUNTS 100 μA auxiliary sink current away from LED #1.
†See Application Hints for optional peak or average detector.
Figure 31. Extended Range VU Meter (Dot Mode)
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R7 thru R15: 10k±10%
D1, D2: 1N914 or 1N4148
*Half-wave peak detector.
See Application Hints.
Figure 32. Driving Vacuum Fluorescent Display
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*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.
Figure 33. Indicator and Alarm, Full-Scale Changes Display From Dot to Bar
*See Application Hints for optional peak or average detector.
Figure 34. High Resolution VU Meter (Bar Mode)
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*Optional shunts 100 μA auxiliary sink current away from LED #1.
†See Application Hints for optional peak or average detector.
Figure 35. High Resolution VU Meter (Dot Mode)
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Figure 36. Displaying Additional Levels
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The LED currents are approximately 10 mA, and LM3916 outputs operate in saturation for minimum dissipation.
*This point is partially regulated and decreases in voltage with temperature. Voltage requirements of the LM3916 also
decrease with temperature.
Figure 37. Operating with a High Voltage Supply (Dot Mode Only)
Supply current drain is only 20 mA with ten LEDs illuminated @ 16 mA.
Figure 38. Low Current Bar Mode Display
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Figure 39. Driving Liquid Crystal Display
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.
Figure 40. Bar Display with Alarm Flasher
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Connection Diagram
Figure 41. Top View
PDIP Package
See Package Number NFK0018A
Definition of Terms
Absolute Accuracy: The difference between the observed threshold voltage and the ideal threshold voltage for
each comparator. Specified and tested with 10V across the internal voltage divider so that resistor ratio
matching error predominates over comparator offset voltage.
Adjust Pin Current: Current flowing out of the reference amplifier pin when the reference amplifier is in the
linear region.
Comparator Gain: The ratio of the change in output current (ILED) to the change in input voltage (VIN) required
to produce it for a comparator in the linear region.
Dropout Voltage: The voltage measured at the current source outputs required to make the output current fall
by 10%.
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 (VLED)
as measured at the current source outputs. As the forward voltage 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.
Line Regulation: The average change in reference output voltage (VREF) over the specified range of supply
voltage (V+).
Load Regulation: The change in reference output voltage over the specified range of load current (IL(REF)).
Offset Voltage: The differential input voltage which must be applied to each comparator to bias the output in
the linear region. Most significant error when the voltage across the internal voltage divider is small.
Specified and tested with pin 6 voltage (VRHI) equal to pin 4 voltage (VRLO).
Relative Accuracy: The difference between any two adjacent threshold points. Specified and tested with 10V
across the internal voltage divider so that resistor ratio matching error predominates over comparator
offset voltage.
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REVISION HISTORY
Changes from Revision A (March 2013) to Revision B
•
28
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 27
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PACKAGE OPTION ADDENDUM
www.ti.com
16-Oct-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM3916N-1
LIFEBUY
PDIP
NFK
18
20
TBD
Call TI
Call TI
0 to 70
LM3916N-1
LM3916N-1/NOPB
LIFEBUY
PDIP
NFK
18
20
Green (RoHS
& no Sb/Br)
Call TI
Level-1-NA-UNLIM
0 to 70
LM3916N-1
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
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16-Oct-2015
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
MECHANICAL DATA
NFK0018A
N0018A
NA18A (Rev B)
www.ti.com
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