LM3916N National Semiconductor, LM3916N Datasheet - Page 8

• 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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Functional Description
The simplified LM3916 block diagram is included to give the
general idea of the circuit’s operation. A high input imped-
ance buffer operates with signals from ground to 12V, and is
protected against reverse and overvoltage signals. The sig-
nal 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
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
For correct operation, reference load current should be be-
tween 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. Ap-
proximately 10 times this current will be drawn through each
1
then flows through the output set resistor
+
and no lower than V
+
and load changes.
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lighted LED, and this current will be relatively constant de-
spite 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 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 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 tran-
sistor 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 satu-
rated.
Outputs 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 R
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 follow-
ing 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
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
+
pin).
LM3916 Output Circuit
LED
).
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plus