LM3915N National Semiconductor, LM3915N Datasheet - Page 10

• Manufacturer Part Number: LM3915N
• Description: IC DRIVER DOT BAR DISPLAY 18-DIP
• Manufacturer: National Semiconductor

Specifications of LM3915N

• 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: *LM3915N; LM3915

Application Hints
TIPS ON REFERENCE VOLTAGE
AND LED CURRENT PROGRAMMING
SINGLE LM3915
The equations in Figure 7 illustrate how to choose resistor
values to set reference voltage for the simple case where
no LED intensity adjustment is required A LED current of 10
mA to 20 mA generally produces adequate illumination
Having 10V full-scale across the internal voltage divider
gives best accuracy by keeping signal level high relative to
the offset voltage of the internal comparators However this
causes 450
means that the LED current will be at least 5 mA R1 will
typically be between 1 k
voltage vary R2
Adjust R2 to vary V
Pick R1
Pick R2
FIGURE 7 Design Equations for Fixed LED Intensity
e
e
I
(V
LED
REF
1 25V R1
b
b
A to flow from pin 7 into the divider which
12 5V
V
REF
REF
1 25V)
2 2 k
a
0 08 mA
and 2 k
(Continued)
To trim the reference
FIGURE 6 Improved Circuit for 60 dB Display
TL H 5104–15
10
Figure 9 shows how to obtain a common reference trim and
The circuit in Figure 8 shows how to add a LED intensity
control which can vary LED current from 9 mA to 28 mA
The reference adjustment has some effect on LED intensity
but the reverse is not true
MULTIPLE LM3915s
intensity control for two LM3915s The two ICs may be con-
nected in cascade for a 60 dB display or may be handling
separate channels for stereo This technique can be ex-
tended for larger numbers of LM3915s by varying the values
of R1 R2 and R3 in inverse proportion to the number of
devices tied in The ICs’ internal references track within 100
mV so that worst case error from chip to chip is only 0 1 dB
for V
9 mA
REF
k
I
LED k
e
10V
FIGURE 8 Varying LED Intensity
28 mA
V
REF
e
10V
TL H 5104 – 14
TL H 5104 – 16