NSC LM3916N-1 Datasheet
LM3916
Dot/Bar Display Driver
LM3916 Dot/Bar Display Driver
January 2000
General Description
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 dotdisplay. LED current drive isregulated
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.
The IC contains an adjustable voltage reference and an accurate 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
parators referenced to the precisiondivider. Accuracyistypically 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 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.
±
35V. The input buffer drives 10 individual com-
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.
Features
n Fast responding electronic VU meter
n Drivers LEDs, LCDs, or vacuum fluorescents
n Bar or dot display mode externally selectable by user
n Expandable to displays of 70 dB
n Internal voltage reference from 1.2V to 12V
n Operates with single supply of 3V to 25V
n Inputs operate down to ground
n Output current programmable from 1 mA to 30 mA
n Input withstands
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 LM3916 is rated for operation from 0˚C to +70˚C. The
LM3916N-1 is available in an 18-lead molded DIP package.
±
35V without damage or false outputs
© 2000 National Semiconductor Corporation DS007971 www.national.com
Typical Applications
LM3916
0V to 10V VU Meter
DS007971-1
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
www.national.com 2
LM3916
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Power Dissipation (Note 6)
Molded DIP (N) 1365 mW
Supply Voltage 25V
Voltage on Output Drivers 25V
±
Input Signal Overvoltage (Note 4)
35V
Divider Voltage −100 mV to V
Reference Load Current 10 mA
Storage Temperature Range −55˚C to +150˚C
Lead Temperature
(Soldering, 10 seconds) 260˚C
Electrical Characteristics (Notes 2, 4)
Parameter Conditions (Note 2) Min Typ Max Units
COMPARATORS
Offset Voltage, Buffer and First Comparator 0V ≤ V
I
LED
Offset Voltage, Buffer and Any Other Comparator 0V ≤ V
I
LED
Gain (∆I
/ ∆VIN)I
LED
(REF)
Input Bias Current (at Pin 5) 0V ≤ V
Input Signal Overvoltage No Change in Display −35 35 V
VOLTAGE DIVIDER
Divider Resistance Total, Pin 6 to 4 8 12 17 kΩ
Relative Accuracy (Input Change
Between Any Two Threshold Points)
(Note 3)
−1 dB ≤ V
−7 dB ≤ V
−10 dB ≤ V
Absolute Accuracy (Note 3)
V
IN
V
IN
V
IN
VOLTAGE REFERENCE
Output Voltage 0.1 mA ≤ I
+
=
V
Line Regulation 3V ≤ V
Load Regulation 0.1 mA ≤ I
Output Voltage Change with Temperature 0˚C ≤ T
+
=
V
+
=
V
Adjust Pin Current 75 120 µA
OUTPUT DRIVERS
+
V
V
=
LED
LED
LED Current V
LED Current Difference (Between Largest and
Smallest LED Currents)
LED Current Regulation 2V ≤ V
I
LED
I
LED
Dropout Voltage I
Saturation Voltage I
LED(ON)
∆I
LED
LED
Output Leakage, Each Collector Bar Mode (Note 5) 0.1 100 µA
Output Leakage Dot Mode (Note 5)
Pins 10–18 0.1 100 µA
Pin 1 60 150 450 µA
=
≤ 12V,
V
RLO
=
1mA
RLO
=
1mA
=
IN
=
2, 1, 0, −1 dB
=
−3, −5 dB
=
−7, −10, −20 dB
V
LED
+
V
LED
V
LED
V
LED
=
=
LED
2mA
=
20 mA
=
=
2.0 mA, I
=
2 mA, I
RHI
≤ 12V,
V
RHI
=
10 mA 3 8 mA/mV
LED
310 mV
315 mV
≤ (V+−1.5V) 25 100 nA
≤ 3dB
IN
≤ −1 dB
IN
IN
L(REF)
=
5Vg
≤ −7 dB
≤ 4 mA,
0.75
1.5
2.5
−0.25
−0.5
−1
1.0
2.0
3.0
1.25
2.5
2.5
+0.25
+0.5
+1
1.2 1.28 1.34 V
≤ 18V 0.01 0.03
≤ 4 mA,
L(REF)
=
5V
≤ +70˚C, I
A
=
5V
= 5V, I
5V, I
LED
5V, I
LED
L(REF)
=
2mA
=
20 mA
=
L(REF)
1 mA,
=
1 mA 7 10 13 mA
0.4 2
1
0.12
1.2
0.4
3
≤ 17V
0.110.25
3
=
20 mA
2mA
L(REF)
=
@
V
5V,
LED
=
0.4 mA 0.15 0.4 V
1.5 V
dB
dB
dB
dB
dB
dB
%
mA
mA
mA
mA
/V
%
%
+
www.national.com3
Electrical Characteristics (Notes 2, 4) (Continued)
LM3916
Parameter Conditions (Note 2) Min Typ Max Units
SUPPLY CURRENT
+
Standby Supply Current
(All Outputs Off)
Note 1: AbsoluteMaximum 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:
3V
≤ V+≤ 20 V
DC
3V
≤ V
LED
RHI
≤ V
≤ 12 V
DC
−0.015V ≤ V
Note 3: Accuracy is measured referred to +3 dB=+10.000 V
comparator offset voltage may add significant error. See table for threshold voltages.
Note 4: Pin 5 input current must be limited to
Note 5: Bar mode results when pin 9 is within 20 mV of V
abled if pin 9 is pulled 0.9V or more below V
Note 6: 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 molded DIP (N package).
DC
+
−0.015V ≤ V
V
REF,VRHI,VRLO
0V ≤ VIN≤ V+− 1.5V
DC
≤ 12 V
RLO
DC
≤ (V+− 1.5V) For higher power dissipations, pulse testing is used.
±
3 mA. The addition of a 39k resistor in series with pin 5 allows±100V signals without damage.
+
LED
.
. Dot mode results when pin 9 is pulled at least 200 mV below V+. LED#10 (pin 10 output current) is dis-
=
V
+ 5V, I
+
=
+ 20V, I
V
=
T
25˚C, I
A
at pin 5, with +10.000 VDCat pin 6, and 0.000 VDCat pin 4. At lower full-scale voltages, buffer and
DC
L(REF)
=
L(REF)
=
0.2 mA
=
L(REF)
0.2 mA, pin 9 connected to pin 3 (bar mode).
1.0 mA
2.4
6.1
4.2
9.2
LM3916 Threshold Voltage (Note 3)
dB
Min Typ Max Min Typ Max
3 9.985 10.000 10.015 −3
1
±
2
⁄
4
8.660 8.913 9.173 −5
1
±
1
⁄
4
7.718 7.943 8.175 −7±1 2.818 3.162 3.548
1
±
0
⁄
4
6.879 7.079 7.286 −10±1 1.995 2.239 2.512
1
±
−1
⁄25.957 6.310 6.683 −20±1 0.631 0.708 0.794
Volts
dB
1
±
⁄
2
4.732 5.012 5.309
1
±
⁄
2
3.548 3.981 4.467
Volts
mA
mA
Typical Performance Characteristics
Supply Current vs
Temperature
DS007971-35
Operating Input Bias
Current vs Temperature
DS007971-36
Reference Voltage vs
Temperature
DS007971-37
www.national.com 4
Typical Performance Characteristics (Continued)
LM3916
Reference Adjust Pin
Current vs Temperature
Input Current Beyond
Signal Range (Pin 5)
DS007971-38
LED Current-Regulation
Dropout
LED Current vs
Referenced Loading
DS007971-39
LED Driver Saturation
Voltage
DS007971-40
LED Driver Current
Regulation
Total Divider Resistance
vs Temperature
DS007971-41
DS007971-44
Common-Mode Limits
DS007971-42
DS007971-45
DS007971-43
Output Characteristics
DS007971-46
www.national.com5
Block Diagram (Showing Simplest Application)
LM3916
www.national.com 6
DS007971-4
LM3916
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
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 I
then flows through the output set resistor
1
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
correct operation, reference load current should be between
80 µA and 5 mA. Load capacitance should be less than
0.05 µF.
+
and no lower than V−.
DS007971-5
+
and load changes. For
LM3916 Output Circuit
DS007971-6
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 R
plus the
E
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)
+
3(V
pin).
directly
to 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 V
LED
).
Mode Pin Functional Description
This pin actually performs two functions. Refer to the simplified 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 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.
*
High for bar
DS007971-7
www.national.com7
Mode Pin Functional Description
(Continued)
LM3916
DOT OR BAR MODE SELECTION
The voltage at pin 9 is sensed by comparator C1, nominally
referenced to (V
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
+
open circuit) for dot mode. In most applications, pin 9 is either open (dot mode) or tied to V
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
ond device comes on. The connection for cascading in dot
mode has already been described and is depicted in
1
.
As long as the input signal voltage is below the threshold of
the second driver,LED
effectively an open circuit so the chip is in dot mode.As soon
+
−100 mV). The chip is in bar mode when
for bar mode and more than 200 mV below V+(or
+
(bar mode). In bar mode,
#
10 of the first device when LED#1 of the sec-
#
11is off. Pin 9 of driver#1 thus sees
Figure
#
as the input voltage reaches the threshold of LED
of driver
V
enced 600 mV below V
#
1 is pulled an LED drop (1.5V or more) below
. This condition is sensed by comparator C2, refer-
LED
. This forces the output of C2 low,
LED
which shuts off output transistor Q2, extinguishing LED
V
is sensed via the 20k resistor connected to pin 11. The
LED
11,pin 9
#
10.
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
#
LED
1) with a 10k resistor. The 1V 1R drop is more than the
900 mV worst case required to hold off LED
enough that LED
#
11 does not conduct significantly.
#
11(and
#
10 yet small
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 V
through two series-connected diodes as shown in
LED
Figure 2
Shunting the diodes with a 1k resistor provides a path for
driver leakage current.
.
FIGURE 1. Cascading LM3914/15/16 Series in Dot Mode
FIGURE 2. Cascading Drivers in Dot Mode with Pin 1 of Driver#2 Unused
www.national.com 8
DS007971-8
DS007971-9
Mode Pin Functional Description
(Continued)
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 witha1mAreference 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 overa1mVrange. The change may be much
more rapid between LED
second
device cascaded.
#
10 of one device and LED#1ofa
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 V
cillations. 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.
to LED anode common can cause os-
LED
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 3
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 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 4
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.
DS007971-10
*
DC Couple
FIGURE 3. Half-Wave Peak Detector
LM3916
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.
www.national.com9
Loading...