LM3914

Manufacturer Part NumberLM3914
ManufacturerTexas Instruments
LM3914 datasheet
 


Specifications of LM3914

Output Channels10Led Voltage(max)(v)17
Pin/package18PDIP, 20PLCCRegulated Outputs(#)10
Iout(max)(a)0.03Led ConfigurationParallel
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Typical Applications
(Continued)
*The exact wiring arrangement of this schematic shows the need for Mode Select (pin 9) to sense the V
Programs LEDs to 10mA
Application Hints
Three of the most commonly needed precautions for using
the LM3914 are shown in the first typical application drawing
showing a 0V–5V bar graph meter. The most difficult prob-
lem occurs when large LED currents are being drawn, espe-
cially 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
(as illustrated) to a single point very near pin 2 is the best
solution.
Long wires from V
to LED anode common can cause
LED
oscillations. Depending on the severity of the problem
0.05µF to 2.2µF decoupling capacitors from LED anode
common to pin 2 will damp the circuit. If LED anode line
wiring is inaccessible, often similar decoupling from pin 1 to
pin 2 will be sufficient.
If LED turn ON seems slow (bar mode) or several LEDs light
(dot 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 sug-
gested limits. Expanded scale meter applications may have
one or both ends of the internal voltage divider terminated at
20-Segment Meter with Mode Switch
+
relatively high value resistors. These high-impedance ends
should be bypassed to pin 2 with at least a 0.001µF capaci-
tor, or up to 0.1µF in noisy environments.
Power dissipation, especially in bar mode should be given
consideration. For example, with a 5V supply and all LEDs
programmed to 20mA the driver will dissipate over 600mW.
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 2.2µF solid tantalum capacitor to
pin 2 of the LM3914.
Turning OFF of most of the internal current sources is ac-
complished by pulling positive on the reference with a cur-
rent source or resistance supplying 100µA or so. Alternately,
the input signal can be gated OFF with a transistor switch.
Other special features and applications characteristics will
be illustrated in the following applications schematics. Notes
have been added in many cases, attempting to cover any
special procedures or unusual characteristics of these appli-
cations. A special section called “Application Tips for the
LM3914 Adjustable Reference” has been included with
these schematics.
15
00797014
voltage exactly as it appears on pin 3.
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