Datasheet

LM3914
SNVS761B –JANUARY 2000–REVISED MARCH 2013 www.ti.com
ADJUSTING LINEARITY OF SEVERAL STACKED DIVIDERS
Three internal voltage dividers are shown connected in series to provide a 30-step display. If the resulting analog
meter is to be accurate and linear the voltage on each divider must be adjusted, preferably without affecting any
other adjustments. To do this, adjust R2 first, so that the voltage across R5 is exactly 1V. Then the voltages
across R3 and R4 can be independently adjusted by shunting each with selected resistors of 6kΩ or higher
resistance. This is possible because the reference of LM3914 No. 3 is acting as a constant current source.
The references associated with LM3914s No. 1 and No. 2 should have their Ref Adj pins (pin 8) wired to ground,
and their Ref Outputs loaded by a 620Ω resistor to ground. This makes available similar 20mA current outputs to
all the LEDs in the system.
If an independent LED brightness control is desired (as in the previous application), a unity gain buffer, such as
the LM310, should be placed between pin 7 and R1, similar to the previous application.
(4.5V to 5V, Bar or Dot Mode)
Figure 26. Non-Interacting Adjustments for Expanded Scale Meter
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