LM3914

SNVS761B – JANUARY 2000 – REVISED MARCH 2013

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MODE PIN FUNCTIONAL DESCRIPTION

This pin actually performs two functions. Refer to the simplified block diagram below.

*High for bar

Figure 14. Block Diagram of Mode Pin Description

DOT OR BAR MODE SELECTION

− 100mV). 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 100mV reference level, pin 9 should be no more than

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 the display to make sense when multiple LM3914s are cascaded in dot mode, special circuitry has

been included to shut off LED No. 10 of the first device when LED No. 1 of the second device comes on. The

connection for cascading in dot mode has already been described and is depicted below.

As long as the input signal voltage is below the threshold of the second LM3914, LED No. 11 is off. Pin 9 of

LM3914 No. 1 thus sees effectively an open circuit so the chip is in dot mode. As soon as the input voltage

which shuts off output transistor Q2, extinguishing LED No. 10.

from LED No. 9 does not noticeably affect its intensity.

An auxiliary current source at pin 1 keeps at least 100

μA flowing through LED No. 11 even if the input voltage

rises high enough to extinguish the LED. This ensures that pin 9 of LM3914 No. 1 is held low enough to force

LED No. 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 No. 11 with a 10k resistor. The 1V IR drop is more than the 900mV worst case

required to hold off LED No. 10 yet small enough that LED No. 11 does not conduct significantly.

10

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