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XR-2279 Datasheet Preview

XR-2279 Datasheet

Dot and Bar-Graph Display Generators

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XR·2279
Dot and Bar-Graph Display Generators
GENERAL DESCRIPTION
FUNCTIONAL BLOCK DIAGRAM
The XR-2279 is a 12 point logarithmic dot or bar-graph
generator/LED driver_ The device compares an input
signal with an adjustable reference and graphically dis-
plays the results_ Since LED driving current is provided
by on board adjustable current sources, no current lim-
iting resistors are required. A special feature of the XR-
2279 is the four highest outputs sink one half the cur-
rent of the lower eight; this allows equivalent bright-
ness with red and green mixed displays.
Dot or bar mode selection is provided. The twelve out-
put levels are in 3 dB steps from - 27 dB to + 6 dB. The
reference point is externally adjustable.
FEATURES
Direct LED Interface
Constant Three dB/Step Logarithmic Scale
External Dot/Bar Mode Select for Dot/Bar-Graph
Formats
Adjustable Output Current Levels
Current Source Outputs
APPLICATIONS
Bar Graph Display Generator
Moving-dot Display Generator
Logarithmic Level Indicator
Sequential Level Indicator
ABSOLUTE MAXIMUM RATINGS
Power Supply
Power Dissipation
Derate Above 25°C
Operating Temperature Range
Storage Temperature Range
15V
625mW
5 mW/oC
O°C to +75°C
- 65°C to + 150°C
ORDERING INFORMATION
Part Number
XR-2279CP
Package
Plastic
Operating Temperature
O°C to + 70°C
SYSTEM DESCRIPTION
The XR-2279 is a 12 point logarithmic level detector cir-
cuit designed for direct interfacing to light emitting di-
ode (LED) moving-dot or bar-graph displays. The circuit
is comprised of an input buffer amplifier and 12 com-
parators which are biased from an internal voltage ref-
erence. Each comparator provides a high impedance
current source output which are all very closely
matched and simultaneously adjustable with a single
external resistor. A control signal applied to the mode
select Pin 18 determines whether the display is driven
in a moving-dot or bar-graph format.
The circuit provides 12 discrete outputs for an input
level range of - 27 dB to + 6 dB, referenced to an inter-
nally set zero dB level, typically 0.2 VRMS. Each step
represents 3 dB, and the reference level is adjustable.
The upper four outputs, 9-12 (see Equivalent Schematic
Diagram), are internally set to provide one-half the cur-
rent out as outputs 1-8. This is for driving red LEOs (as
over-range indicators) which require less current than
other colors.
1-251




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XR-2279 Datasheet Preview

XR-2279 Datasheet

Dot and Bar-Graph Display Generators

No Preview Available !

XR·2279
ELECTRICAL CHARACTERISTICS
Test Conditions: VCC = 12 Volts, TA = 25°C, unless otherwise specified. (See Test Circuit of Figure 2.)
XR-2279
PARAMETERS
Supply Voltage
Supply Current
Output Current
Outputs 1 through 8
Outputs 9 through 12
Output Current Matching
Outputs 1 through 8
Outputs 9 through 12
Maximum Drive Current
Outputs 1 through 8
Outputs 9 through 12
Input Voltage for 0 dB Output
Input Current
Outputs
Output 1 (Pin 7)
Output 2 (Pin 16)
Output 3 (Pin 15)
Output 4 (Pin 14)
Output 5 (Pin 13)
Output 6 (Pin 12)
Output 7 (Pin 11)
Output 8 (Pin 10)
Output 9 (Pin 5)
Output 10 (Pin 6)
Output 11 (Pin 7)
Output 12 (Pin 8)
MIN
10
12
6
-2.0
-1.0
0.10
-25.5
-22.5
-19.5
-16.5
-13.5
-10.5
-7.0
-4.0
+2.0
+4.5
TYP
12
5
15
8
0.20
50
-27
-24.0
-21.0
-18.0
-15.0
-12.0
-9.0
-6.0
-3.0
0
+3.0
+6.0
MAX
14
10
18
10
+2.0
+1.0
22
11
0.25
-22.5
-19.5
-16.5
-13.5
-10.5
-7.5
-5.0
-2.0
+4.0
+7.5
UNITS
VDC
mA
mA
mA
mA
mA
mA
mA
VRMS
nA
CONDITIONS
VF(LED) = 2V
VIN = OV
R2 = 27KO
Measured at Pins 10 through 17
Measured at Pins 5 through 8
R2 = 27KO
Measured at Pins 10 through 17
Measured at Pins 5 through 8
R2 varied - see Figure 4
Measured at Pins 10 through 17
Measured at Pins 5 through 8
o dB Output Threshold
Measured at Pin 3
dB See Note 1
dB
dB
dB
dB
dB
dB
dB
dB
dB See Note 1
dB
dB
Note 1:
Determine exact value of input voltage to produce zero dB output. This is done by increasing the ac input signal
amplitude until Output 10 (Pin 6) begins conduction.
Reduce input voltage level to - 27 dB referenced to the input level of Note 1. Adjust R1 until Output 1 (Pin 17)
begins conduction.
EQUIVALENT SCHEMATIC DIAGRAM
OUTPUT
CURRENT AD.I.
1-252


Part Number XR-2279
Description Dot and Bar-Graph Display Generators
Maker Exar
Total Page 4 Pages
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