LM3916N National Semiconductor, LM3916N Datasheet - Page 10

• Manufacturer Part Number: LM3916N
• Description: IC DRIVER DOT BAR DISPLAY 18-DIP
• Manufacturer: National Semiconductor

Specifications of LM3916N

• Display Type: LED, LCD, Vacuum Fluorescent
• Configuration: Dot/Bar Display
• Digits Or Characters: 10 Steps
• Current - Supply: 6.1mA
• Voltage - Supply: 3 V ~ 25 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 18-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Interface: -
• Other names: *LM3916N; LM3916

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Mode Pin Functional Description
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
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
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 “over-
lap” 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 cur-
rents 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 bot-
tom of the resistor string to a single point very near pin 2 is
the best solution.
Long wires from V
oscillations. The usual cure is bypassing the LED anodes
with a 2.2 µF tantalum or 10 µF aluminum electrolytic ca-
pacitor. 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 oscil-
lations, V
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.
+
voltage at pin 3 is usually below suggested limits.
+
pin supply. At full-scale, the IC is typically
LED
to LED anode common can cause
FIGURE 2. Cascading Drivers in Dot Mode with Pin 1 of Driver #2 Unused
+
(pin 3) supply input. For
(Continued)
10
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 illumi-
nated represents the instantaneous value of the AC wave-
form, one can readily discern both peak and average values
of audio signals in this manner. The LM3916 will respond to
positive half-cycles only but will not be damaged by signals
up to
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.
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
±
35V (or up to
±
100V if a 39k resistor is in series with
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