LM1269
110 MHz I
2
C Compatible RGB Video Amplifier System
with OSD & DACs
General Description
The LM1269 pre-amp is an integrated CMOS CRT pre-amp.
The IC is I
2
C compatible, and allows control of all the pa-
rameters necessary to directly setup and adjust the gain and
contrast in the CRT display. Brightness and bias can be
controlled through the DAC outputs, and is well matched to
the LM2479 and LM2480 integrated bias clamp IC.
The LM1269 pre-amp is designed to work in cooperation
with the LM246X high gain driver family.
Black level clamping of the signal is carried out directly on
the AC coupled input signal into the high impedance pream-
plifier input, thus eliminating the need for additional black
level clamp capacitors.
The IC is packaged in an industry standard 24-lead DIP
molded plastic package.
Features
n
I
2
C compatible interface
n
110 MHz bandwidth preamplifier with full video signal
parametric control
n
4 external 8-bit DACs for bus controlled Bias and
Brightness
n
Suitable for use with discrete or integrated clamp, with
software configurable Brightness mixer
n
Power Save (Green) Mode, 80% power reduction
n
Matched to LM246X driver
Applications
n
Low end 14', 15', and 17' bus controlled monitors with
OSD
n
1024 X 768 displays up to 70 Hz requiring OSD
capability
n
Very low cost system with LM246X driver
Block and Connection Diagram
DS200099-1
FIGURE 1. Order Number LM1269NA
See NS Package Number N24D
May 2002
LM1269
1
1
0
MHz
I
2
C
Compatible
RGB
V
ideo
Amplifier
System
with
OSD
&
DACs
2002 National Semiconductor Corporation
DS200099
www.national.com
Absolute Maximum Ratings
(Notes 1, 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage, Pin 9
6.0V
Peak Video Output Source Current
(Any One Amp)
Pins 18, 19, or 20
28 mA
Voltage at Any
Input Pin (V
IN
)
V
CC
+0.5
>
V
IN
>
-0.5V
Power Dissipation (P
D
)
(Above 25C Derate based on
JA
and T
J
)
2.4W
Thermal Resistance to Ambient (
JA
)
51C/W
Thermal Resistance to Case (
JC
)
32C/W
Junction Temperature (T
J
)
150C
ESD Susceptibility (Note 4)
3.5 kV
ESD Machine Model (Note 5)
350V
Storage Temperature
-65C to +150C
Lead Temperature
(Soldering, 10 sec.)
265C
Operating Ratings
(Note 2)
Temperature Range
0C to 70C
Supply Voltage (V
CC
)
4.75V
<
V
CC
<
5.25V
Video Inputs
0.0V
<
V
IN
<
1.0V
P-P
Active Video Signal Electrical Characteristics
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Output = 2 V
P-P
.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
I
S
Maximum Supply Current
Test Setting 1, R
L
=
(Note
8)
200
225
mA
I
S-PS
Maximum Supply Current,
Power Save Mode
Test Setting 1, R
L
=
, Bit 1 of
Reg. 9 = 1 (Note 8)
42
60
mA
LE
Linearity Error
Test Setting 4, Triangular
signal input source (Note 9)
5
%
V
O Blk Typ
Typical Video Black Level
Output
Test Setting 4, No AC Input
Signal, DC = 5 Hex, or 0.5V
Offset
1.05
1.25
1.45
VDC
V
O Blk Step
Video Black Level Step Size
Test Setting 4, No AC Input
Signal
60
90
120
mV
V
O
/
V
CC
Variation in Output Video Black
Level vs V
CC
Variations
Test Setting 1 & 3, No AC
Input Signal, 4.75
<
V
CC
<
5.25
-0.25
0
0.25
mV/V
V
O White-Max
White Level Video Output
Voltage
Test Setting 3, Video in = 0.7V
4.0
4.2
V
V
Blank
Blanked Output Level
Test Setting 4, AC Input Signal
0
0.2
0.5
V
t
r
Rise Time
10% to 90%, Test Setting 4,
AC Input Signal (Note 10)
3.9
ns
OS
R
Overshoot (Rising Edge)
Test Setting 4, AC Input Signal
(Note 10)
1
%
t
f
Fall Time
90% to 10%, Test Setting 4,
AC Input Signal (Note 10)
3.5
ns
OS
F
Overshoot (Falling Edge)
Test Setting 4, AC Input Signal
(Note 10)
1
%
f(-3 dB)
Video Amplifier Bandwidth
(Note 13)
Test Setting 8
110
MHz
V
sep
10 kHz
Video Amplifier 10 kHz
Isolation
Test Setting 8 (Note 14)
-70
dB
V
sep
10 MHz
Video Amplifier 10 MHz
Isolation
Test Setting 8 (Note 14)
-50
dB
A
V Max
Maximum Voltage Gain
Test Setting 8, AC Input Signal
4
V/V
A
V
1
/
2
Contrast
@
50% Level
Test Setting 5, AC Input Signal
-10
dB
A
V Min
Maximum Contrast Attenuation
Test Setting 2, AC Input Signal
-20
dB
A
V Gain
1
/
2
Gain
@
50% Level
Test Setting 6, AC Input Signal
-5
dB
A
V Gain Min
Maximum Gain Attenuation
Test Setting 7, AC Input Signal
-10
dB
A
V Match
Absolute Gain Match
@
A
V Max
Test Setting 3, AC Input Signal
0.5
dB
LM1269
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2
Active Video Signal Electrical Characteristics
(Continued)
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Output = 2 V
P-P
.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
A
V Track
Gain Change between
Amplifiers
Tracking when Changing from
Test Setting 8 to Test Setting 5
(Note 11)
0.5
dB
V
ABL TH
ABL Control Upper Limit
Test Setting 4, AC Input Signal
(Note 12)
5
V
V
ABL Range
ABL Control Voltage Active
Range
Test Setting 4, AC Input Signal
(Note 12)
2
V
A
ABL
ABL Control Range
Test Setting 4, AC Input Signal
(Note 12)
-8
dB
I
ABL Active
ABL Input Bias Current during
ABL
Test Setting 4, AC Input
Signal, V
ABL
= 2V(Note 12)
0
10
A
I
ABL Max
ABL Input Current Clamp Sink
Capability
Test Setting 4, AC Input Signal
(Note 12)
1
mA
V
Clamp Max
Clamp Gate Low Input Voltage
Clamp Comparators Off
1.4
V
V
Clamp Min
Clamp Gate High Input Voltage
Clamp Comparators On
2.6
V
I
Clamp
Clamp Gate Input Current
V
23
= 0V to V
CC
- 1V
-5
0.1
10
A
t
PW Clamp
Back Porch Clamp Pulse Width
(Note 15)
200
ns
t
Clamp-Video
End of Clamp Pulse to Start of
Active Video
Limit is guaranteed by design
200
nsec
R
In-Video
Input Resistance
Test Setting (4)
20
M
I
In-Video
Input Bias Current
Test Setting (4)
0.1
10
A
V
Ref
Out
V
Ref
Output Voltage
10 k
, 1% Resistor; Pin 10 to
GND
1.25
1.40
1.55
V
V
Spot
Spot Killer Voltage
V
CC
Adjusted to Activate
3.6
4.0
4.25
V
OSD Electrical Characteristics
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Signal Output = 2 V
P-P
, Test Set-
ting 8.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
V
OSD-L
OSD Input Low Input
Operating Range
OSD Inputs are Selected
1.2
V
V
OSD-H
OSD Input High Input
Operating Range
OSD Inputs are Selected
2.5
V
I
OSD
OSD Input Current
V
OSD
= 0V to V
CC
- 1V
-5
0.1
10.0
A
V
OSD-Sel-L
OSD Select Low Input
Operating Range
Video Inputs are Selected
1.2
V
V
OSD-Sel-H
OSD Select High Input
Operating Range
OSD Inputs are Selected
2.5
V
I
OSD-Sel
OSD Select Input Current
V
OSD-Sel
= 0V to V
CC
- 1V
-5
0.1
10
A
V
O-OSD(Blk)
OSD
Black Level Output
Voltage, Difference from Video
Output
Register 08 = 18, Minimum
Video Black Level
45
150
mV
V
O-OSD(Blk)
Range of OSD Black Level
Output Voltage between the 3
Channels
Register 08 = 18, Minimum
Video Black Level
-100
0
+100
mV
V
OSD-out
OSD Output Voltage, Percent
of Maximum Video Out
Register 08 = 18, Minimum
Video Black Level
75
88
100
%
V
OSD-out
OSD Output V
P-P
Attenuation
Register 08 = 08
58
63
68
%
V
OSD-out
(Track)
Output Variation between
Channels
Register 08 Changed from 18
to 08
3.0
5.0
%
LM1269
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3
OSD Electrical Characteristics
(Continued)
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Signal Output = 2 V
P-P
, Test Set-
ting 8.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
t
OSD/OSD S
Output Skew Time between
OSD and OSD Select
Measured from 50% Point on
all Waveforms
2.0
ns
V
feed
10 kHz
Video Feedthrough into OSD
OSD Inputs = 0V
-70
dB
V
feed
10 MHz
Video Feedthrough into OSD
OSD Inputs = 0V
-60
dB
External DAC Signals Electrical Characteristics
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Signal Output = 2 V
P-P
. The fol-
lowing apply for all four external DACs.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
V
Min DAC
Min DAC Output Voltage
Value = 00h
0.5
0.75
V
V
Max DAC
Mode 00
Max DAC Output Voltage
Value = FFh, DCF[1:0] = 00h
(no load)
3.6
4.2
V
V
Max DAC
Mode 11
Max Output Voltage of DACs
13 in DCF Mode 11
Value = FFh, DCF[1:0] = 11h,
DAC4 Value = 00h
1.85
2.1
2.35
V
V
Max DAC
(Temp)
Variation of any DAC output
voltage with temperature
0C
<
T
<
70C ambient
0.5
mV/deg
V
Max DAC
(V
CC
)
Variation of any DAC output
voltage with V
CC
4.75V
<
V
CC
<
5.25V
50
mV/V
Linearity
Linearity of DAC Over its
Range
5
%
Monotonicity
Monotonicity of the DAC
Excluding dead zones at limits
of DAC
0.5
LSB
External Interface Signals Electrical Characteristics
Unless otherwise noted: T
A
= 25C, V
CC
= +5V, V
IN
= 0.7V, V
ABL
= V
CC
, C
L
= 8 pF, Video Output = 2 V
P-P
.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
V
l
(I
2
C)
I
2
C Low Input Voltage
SDA or SCL Inputs
-0.5
0.5
1.5
V
V
h
(I
2
C)
I
2
C High Input Voltage
SDA or SCL Inputs
3.0
4.0
5.0
V
I
l
(I
2
C)
I
2
C Low Input Current
SDA or SCL Inputs, Input
Voltage = 0V
1.9
2.2
2.5
A
I
h
(I
2
C)
I
2
C High Input Current
SDA or SCL Inputs, Input
Voltage = 5V
0.3
0.6
0.9
A
t
H-Blank on
H-Blank Time Delay from Zero
Crossing Point of H Flyback
Rising Edge of the Flyback
Signal
50
ns
t
H-Blank off
H-Blank Time Delay from Zero
Crossing Point of H Flyback
Falling Edge of the Flyback
Signal
50
ns
I
In Threshold
I
In
H-Blank Detection
Threshold
-20
A
I
In-Operating
Minimum -- Insure Normal
Operation
Maximum -- Should Not
Exceed in Normal Operation
Lowest Operating Horizontal
Frequency in Given Application
(Note 17)
-30
-300
A
I
In Flyback
Peak Current during Flyback
Period, Recommended Design
Range
Operating Range for all
Horizontal Scan Frequencies,
Maximum Current Should Not
Exceed 2 mA (Note 17)
0.5
1.5
2.0
mA
Note 1: Limits of Absolute Maximum Ratings indicate limits below which damage to the device must not occur.
Note 2: Limits of operating ratings indicate required boundaries of conditions for which the device is functional, but may not meet specific performance limits.
LM1269
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4
External Interface Signals Electrical Characteristics
(Continued)
Note 3: All voltages are measured with respect to GND, unless otherwise specified.
Note 4: Human body model, 100 pF discharged through a 1.5 k
resistor.
Note 5: Machine Model ESD test is covered by specification EIAJ IC-121-1981. A 200 pF cap is charged to the specified voltage, then discharged directly into the
IC with no external series resistor (resistance of discharge path must be under 50
).
Note 6: Typical specifications are specified at +25C and represent the most likely parametric norm.
Note 7: Tested limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 8: The supply current specified is the quiescent current for V
CC
with R
L
=
. Load resistors are not required and are not used in the test circuit, therefore all
the supply current is used by the pre-amp.
Note 9: Linearity Error is the variation in step height of a 16 step staircase input signal waveform with 0.7 V
P-P
level at the input, subdivided into 16 equal steps,
with each step approximately 100 ns in width.
Note 10: Input from signal generator: t
r
, t
f
<
1 ns. Scope and generator response used for testing: t
r
= 1.1 ns, t
f
= 0.9 ns. Using the RSS technique the scope and
generator response have been removed from the output rise and fall times.
Note 11:
A
V
track is a measure of the ability of any two amplifiers to track each other and quantifies the matching of the three gain stages. It is the difference in
gain change between any two amplifiers with the contrast set to A
V
1
/
2
and measured relative to the A
V
max condition. For example, at A
V
max the three amplifiers'
gains might be 12.1 dB, 11.9 dB, and 11.8 dB and change to 2.2 dB, 1.9 dB and 1.7 dB respectively for contrast set to A
V
1
/
2
. This yields a typical gain change of
10.0 dB with a tracking change of
0.2 dB.
Note 12: ABL should provide smooth decrease in gain over the operational range of 0 dB to 6 dB
A
ABL
= A(V
ABL
= V
ABL Max Gain
) - A(V
ABL
= V
ABL Min Gain
)
Beyond 6 dB the gain characteristics, linearity, pulse response, and/or behavior may depart from normal values.
Note 13: Adjust input frequency from 10 MHz (A
V
max reference level) to the -3 dB corner frequency (f
-3 dB
).
Note 14: Measure output levels of the other two undriven amplifiers relative to the driven amplifier to determine channel separation. Terminate the undriven amplifier
inputs to simulate generator loading. Repeat test at f
IN
= 10 MHz for V
sep 10 MHz
.
Note 15: A minimum pulse width of 200 ns is guaranteed for a horizontal line of 15 kHz. This limit is guaranteed by design. If a lower line rate is used then a longer
clamp pulse may be required.
Note 16: The video black level is used for this test. OSD amplitude is measured from the video black level to the OSD white level.
Note 17: Limits met by matching the external resistor going to pin 24 to the H Flyback voltage.
LM1269
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5
Typical Performance Characteristics
V
CC
= 5V, T
A
= 25 unless otherwise specified.
Gain Attenuation
DS200099-2
Contrast Attenuation
DS200099-3
ABL Attenuation
DS200099-4
Rise and Fall Times
DS200099-5
Contrast vs Frequency
DS200099-6
Gain vs Frequency
DS200099-7
LM1269
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6
Test Circuit
Test Settings
Control
No.
of
Bits
Basic
Test
Setting 1
Basic
Test
Setting 2
Basic
Test
Setting 3
Basic
Test
Setting 4
Basic
Test
Setting 5
Basic
Test
Setting 6
Basic
Test
Setting 7
Basic
Test
Setting 8
Contrast
7
Max
(Hex 7F)
Min
(Hex 00)
Max
(Hex 7F)
Max
(Hex 7F)
50%
(Hex 40)
Max
(Hex 7F)
Max
(Hex 7F)
Max
(Hex 7F)
R, G, B Gain
7
Max
(Hex 7F)
Max
(Hex 7F)
Max
(Hex 7F)
Set Video
Output to
2V
P-P
Max
(Hex 7F)
50%
(Hex 40)
Min
(Hex 00)
Max
(Hex 7F)
Video DC Offset
& OSD Contrast
5
Min
(Hex 18)
Min + 0.5V
(Hex 1D)
Max
(Hex 07)
Min + 0.5V
(Hex 1D)
Min + 0.5V
(Hex 1D)
Min + 0.5V
(Hex 1D)
Min + 0.5V
(Hex 1D)
Min + 0.5V
(Hex 1D)
Timing Diagrams
DS200099-10
Note: 8 pF load includes parasitic capacitance.
DS200099-11
FIGURE 2. Blanking Propagation Delay
LM1269
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7
Timing Diagrams
(Continued)
Pin Descriptions
Pin No.
Pin Name
Schematic
Description
1
2
3
Red OSD Input
Green OSD Input
Blue OSD Input
These inputs accept standard TTL or CMOS
inputs. Each color is either fully on (logic
high) or fully off (logic low). Unused pins
should be connected to ground with a 47k
resistor.
4
OSD Select
This input accepts a standard TTL or CMOS
input.
H = OSD
L = Video
Connect to ground with a 47k resistor if not
using OSD.
DS200099-12
FIGURE 3. OSD Output Skew
LM1269
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8
Pin Descriptions
(Continued)
Pin No.
Pin Name
Schematic
Description
5
6
7
Red Video In
Green Video In
Blue Video In
Video inputs. These inputs must be AC
coupled with a 4.7 nF cap. DC restoration is
done at these inputs. A series resistor of
about 33
and external ESD protection
diodes should also be used for ESD
protection.
8
Analog Ground
Ground Pin for the analog circuits of the
LM1269.
9
V
CC
Power supply pin for LM1269.
10
V
ref
R
ext
Sets the internal current sources through a
10 k
1% external resistor. Resistor value
and accuracy is critical for optimum
operation of the LM1269.
11
SDA
The I
2
C data line. A pull-up resistor of about
2 k
should be connected between this pin
and +5V. A 300
resistor should be
connected in series with the data line for
protection against arcing.
12
SCL
The I
2
C Clock line. A pull-up resistor of
about 2 k
should be connected between
this pin and +5V. A 300
resistor should be
connected in series with the clock line for
protection against arcing.
13
14
15
16
DAC4
DAC3
DAC2
DAC1
DAC outputs for cathode cut-off adjustments
and brightness control. DAC 4 can be set to
change the outputs of the other three DACs,
acting as the brightness control. The DACs
are set through the I
2
C bus.
17
Digital Ground
Ground Pin for the digital circuits of the
LM1269.
LM1269
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9
Pin Descriptions
(Continued)
Pin No.
Pin Name
Schematic
Description
18
19
20
Blue Video Out
Green Video Out
Red Video Out
Video outputs of the LM1269. The ideal
driver for this part is the LM246X CRT driver
family, which has the necessary gain of 26
dB or 20 V/V.
21
V
Ref
Out
A 0.1 F capacitor must be placed close to
this pin for decoupling the internal V
Ref
. This
pin may be used for an external voltage
reference with proper buffering.
22
ABL
The Auto Beam Limit control reduces the
gain of the video amplifier in response to a
control voltage proportional to the CRT beam
current. The ABL acts identically on all three
channels. ABL is required for CRT life and
X-ray protection.
23
Clamp Pulse
This input accepts a standard TTL or CMOS
input. A positive signal activates the clamp
pulse for DC restoration of the video input.
The AC coupling capacitors at the video
inputs are used for holding the DC correction
voltage, eliminating the need for additional
capacitors.
24
H Flyback
H flyback is an analog signal input from the
monitor horizontal scan. The LM1269 is able
to generate an accurate blanking pulse in
the video outputs from this input. The
horizontal flyback from the monitor must be
a clean signal, with no ringing or other noise
on the signal.
LM1269
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10
Functional Description
All functions of the LM1269 are controlled through the I
2
C
Bus. Details on the internal registers are covered in the
I
2
C Interface Registers Section.
Figure 1 shows the block
diagram of the LM1269. The I
2
C signals come in on pins
11 and 12 and go to the I
2
C Interface. Both the internal
blocks with an "R" and the four external DACs are con-
trolled by the I
2
C Interface. The video and OSD blocks
are shown for the red channel in
Figure 1. The blocks for
both the green and blue channels are not shown; how-
ever, they are identical to the red channel.
Proper operation of the LM1269 does require a very
accurate reference voltage. This voltage is generated in
the V
Ref
block. To insure an accurate voltage over tem-
perature, an external resistor is used to set the current in
the V
Ref
stage. The external resistor is connected to pin
10. This resistor should be 1% and have a temperature
coefficient under 100 ppm/C. ALL VIDEO SIGNALS
MUST BE KEPT AWAY FROM PIN 10. This pin has a very
high input impedance and will pick up any high frequency
signals routed near it. The board layout shown in
Figure
10 is a good example of trace routing near pin 10. The
output of the V
Ref
stage goes to a number of blocks in the
video section and also to pin 21. This pin allows capacitor
filtering on the V
Ref
output and offers an accurate external
reference. A buffer must be used with this reference, the
maximum current loading should be only 100 A.
Note: Any noise injected into pin 21 will appear on the video. The voltage
reference must be kept very clean for best performance of the
LM1269.
The video inputs are pins 5, 6, and 7. Looking at the red
channel (pin 5) note that the "Clamp DC Restore Amp" is
connected to this pin. Since the video must be AC coupled to
the LM1269, the coupling cap is also used to store the
reference voltage for DC restoration. The "Clamp DC Re-
store Amp" block charges the input capacitor to the correct
voltage when the clamp pulse (pin 23) is active. The "Hi Z
Input Buffer Amp" buffers the video signal for internal pro-
cessing. Input impedance to this stage is typically 20 M
.
With such a high impedance the DC restoration can appear
to be working for a number of minutes after the clamp pulse
is removed.
The output of the Buffer Amp goes to the Contrast stage. The
7 bit contrast register (03h) sets the contrast level through
the I
2
C bus. This register controls the Contrast stage in each
video channel. Contrast adjustment range is up to -20 dB.
Loading all zeros in the contrast register gives -20 dB at-
tenuation. All ones will give no attenuation. The output of this
stage is used as the feedback for the DC restoration loop.
"Auto Beam Limit Amp" or ABL is the next block in the video
path. This is a voltage controlled gain stage which gives no
attenuation with 5V at pin 22 and gives about -10 dB attenu-
ation with 2V at pin 2. ABL is covered in more detail later in
this section.
Next in the video path is the "OSD Mixer". The OSD Select
signal at pin 4 controls this stage, selecting OSD with a high
at pin 4, and video with a low at pin 4. Since the DC
restoration feedback is at the Contrast output, the video
black level will match the OSD black level. The OSD signal is
mixed with the video signal at the output of this stage.
The OSD goes through the "OSD Contrast" stage before
entering the "OSD Mixer" block. Bits 3 and 4 of register 08h
control the OSD contrast giving four video levels for the OSD
window. Maximum video level for the OSD window occurs
with both bits set to one. Minimum video level will occur with
both bits set to a zero.
Following the "OSD Mixer" is the "Gain" block. Each video
channel has its own independent control of this block so the
user can balance the color of the CRT display. Registers
00h, 01h, 02h are used for the gain attenuation. These
registers are 7 bits with the maximum attenuation of -10 dB
occurring when all zeros are loaded.
The final block in the video path is the "Output Buffer Amp".
This stage provides the drive needed for the inputs of a CRT
driver. The recommended driver for this pre-amp is one of
the LM246X family. Horizontal blanking is also added to the
video signal from the "H Blank" stage. This block is covered
in more detail below. DC offset of the output is set by the "DC
DACs Offset" stage. Bits 0 through 2 in register 08 control
this stage. This gives 8 different black levels ranging from
0.75V to 1.55V. When using one of the LM246X CRT driver
family it is recommended that the black level be set to 1.25V.
ABL: The Auto Beam Limit control reduces the gain of the
video amplifiers in response to a control voltage proportional
to the CRT beam current. The ABL acts on all three channels
in an identical manner. This is required for CRT life and X-ray
protection. The beam current limit circuit application is as
shown in
Figure 4: when no current is being drawn by the
EHT supply, current flows from the supply rail through the
ABL resistor and into the ABL input of the IC. The IC clamps
the input voltage to a low impedance voltage source (the 5V
supply rail).
When current is drawn from the EHT supply, some of the
current passing through the ABL resistor goes to the EHT
supply, which reduces the current flowing into the ABL input
of the IC.
When the EHT current is high enough, the current flowing
into the ABL input of the IC drops to zero. This current level
determines the ABL threshold and is given by:
Where:
V
S
is the external supply (usually the CRT driver supply rail,
about 80V)
V
ABL TH
is the threshold ABL voltage of the IC
R
ABL
is the ABL resistor value
I
ABL
is the ABL limit
When the voltage on the ABL input drops below the ABL
threshold of the pre-amp, the gain of the pre-amp reduces,
which reduces the beam current. A feedback loop is thus
established which acts to prevent the average beam current
exceeding I
ABL
.
LM1269
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11
Functional Description
(Continued)
H Flyback: H Flyback is an analog signal input from the
monitor horizontal scan. The "H Blank" section uses this
signal to add horizontal blanking to the output video signal.
This enables the user to blank at the cathodes during hori-
zontal flyback. An optional capacitor and/or resistor to
ground may be needed if noise interferes with the H Flyback
signal.
This feature gives very accurate timing for the horizontal
blanking; however, the flyback signal must be very clean.
There should be no ringing or other noise on the flyback
signal.
R
LIMIT
is used to limit the input current into the IC to a typical
value of + 1 mA during flyback and -100 A during normal
forward scan. For example if an H flyback with a peak of
100V is used, R
LIMIT
= 100 k
. The internal input impedance
of pin 24 is low to limit the maximum voltage swing at the
input to within the supply rail and ground. The IC interface
circuit creates a digital signal from this waveform, which is
used as the blanking signal at the "Output Buffer Amp". This
signal adds blanking to the video output signal.
Figure 5
shows the H flyback waveforms and the location of R
LIMIT
. A
56 pF capacitor has been added to the H Flyback pin on the
demo board for filtering noise on the H Flyback signal.
H Blank: Some customers may still prefer to use a standard
logic signal for the horizontal blanking. Pin 24 can be
adapted to accept a logic input. It is necessary for the current
flow into pin 24 to reverse for proper operation. Therefore the
logic signal must be AC coupled into pin 24.
Figure 6 shows
the recommended circuit for a logic signal input. The blank
signal must be a positive pulse.
Power Save Mode: There are two modes of power save:
1.
Blanking the video
2.
Turning off most of the power for maximum power sav-
ings.
In the first mode the video is completely blanked. By setting
bit-0 in register 9 to a 1 the video will be completely blanked.
This gives some power savings since there is no beam
current in the monitor. Maximum power saving is obtained in
the second mode. Bits 0 and 1 in register 9 should be set to
a 1. Bit 1 in register 9 turns off the video output stage of the
DS200099-26
FIGURE 4. ABL
DS200099-27
FIGURE 5. H Flyback Input Pulse
DS200099-28
FIGURE 6. Standard Logic H Blank
LM1269
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12
Functional Description
(Continued)
LM1269, giving a high impedance at the output pin. After bits
0 and 1 of register 9 are set to a 1, the power supplies to the
CRT driver and CRT can be turned off.
Note: The 5V supply must remain on for proper operation. Since the LM1269
is a CMOS device its power consumption will be minimal.
External DACs: Four DACs with external outputs are pro-
vided in the LM1269. Normally these DACs will be used for
color balance and brightness control. If the brightness con-
trol is done at G1, then three DACs would be used for color
balance and the last DAC would be used for controlling the
G1 voltage.
There is also a provision to set the brightness at the cath-
odes. DAC 4 can be set to vary the outputs of the other three
DACs after the color balance is completed. This is accom-
plished by adding the output of DAC 4 to the other 3 DACs.
Bits 3 and 4 of register 9 are set to a 1 for brightness control
at the cathodes. Bit 3 sets the output range of DAC 13 to
50% of their full range. Bit 4 adds 50% of DAC 4 to the other
three DACs. These two adjustments keeps the overall output
voltage of DAC 13 in the proper range and still allows
brightness control. For either mode of brightness control, the
DACs are ideally set to work with the LM2479 or LM2480 for
DC restoration at the cathodes of the CRT.
ESD and Arc-Over Protection
The LM1269 incorporates full ESD protection with special
consideration given to maximizing arc-over robustness. The
monitor designer must still use good circuit design and PCB
layout techniques. The human body model ESD susceptibil-
ity of the LM1269 is 3.5 kV, however many monitor manu-
facturers are now testing their monitors to the level 4 of the
IEC 801-2 specification which requires the monitor to survive
an 8 kV discharge. External ESD protection is needed to
survive this level of ESD. The LM1269 provides excellent
protection against both ESD and arc-over, but this is not a
substitute for good PCB layout.
Figure 7 shows the recommended input protection for the
LM1269. This provides the best protection against ESD.
When this protection is combined with good PCB layout the
LM1269 will easily survive the IEC 801-2 level 4 testing (8 kV
ESD). It is strongly recommended that the protection diodes
be added as shown in
Figure 7. The 1N4148 diode has a
maximum capacitance of 4 pF, which will have little effect on
the response of the video system due to the low impedance
of the input video.
The ESD cells of the LM1269 also provide good protection
against arc-over, however good PCB layout is necessary.
The LM1269 should not be exposed directly to the voltages
that may occur during arc-over. The main vulnerability of the
LM1269 to arc-over is though the ground traces on the PCB.
For proper protection all ground connections associated with
the LM1269, including the grounds to the bypass capacitors,
must have short returns to the ground pins. A significant
ground plane should be used to connect all the LM1269
grounds.
Figure 10, which shows the demo board layout, is
an excellent example of an effective ground plane. The list
below should be followed to ensure a PCB with good
grounding:
All grounds associated with the LM1269 should be con-
nected together through a large ground plane.
CRT driver ground is connected to the video pre-amp
ground at one point.
CRT and arc protection grounds are connected directly to
the chassis or main ground. There is no arc-over current
flow from these grounds through the LM1269 grounds.
Input signal traces for SDA, SCL, H Flyback, and Clamp
should be kept away from the CRT driver and all traces
that could carry the arc current.
Output signal traces of the LM1269 should be kept away
from the traces that carry the output signals of the CRT
driver.
If any one of the above suggestions is not followed the
LM1269 may become more vulnerable to arc-over. Improper
grounding is by far the most common cause of video pre-
amp failure during arc-over.
DS200099-29
FIGURE 7. Recommended Video Input ESD Protection
LM1269
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13
Schematic
DS200099-30
FIGURE
8.
LM126X/LM246X
Neck
Board
Schematic
LM1269
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14
Schematic
(Continued)
DS200099-34
FIGURE
9.
LM126X/LM246X
Neck
Board
Schematic
(Continued)
LM1269
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15
PCB Layout
Micro-Controller Interface
The micro-controller interfaces to the LM1269 pre-amp via
an I
2
C interface. The protocol of the interface begins with the
Start Pulse followed by a byte comprised of a seven-bit
Slave Device Address and a Read/Write bit as the LSB.
Therefore the address of the LM1269 for writing is DCh
(1101 1100) and the address for reading is DDh (1101 1101).
Figures 11, 12 show a write and read sequence across the
I
2
C interface.
Write Sequence
The write sequence begins with a start condition which
consists of the master pulling SDA low while SCL is held
high. The slave device address is next sent. The address
byte is made up of an address of seven bits (71) and the
read/write bit (0). Bit 0 is low to indicate a write operation.
Each byte that is sent is followed by an acknowledge. When
SCL is high the master will release the SDA line. The slave
must pull SDA low to acknowledge. The address of the
register to be written to is sent next. Following the register
address and the acknowledge bit the data for the register is
sent. If bit 0 of register 0Ah is set low (default value) then the
LM1269 is set for the increment mode. In this mode when
more than one data byte is sent it is automatically incre-
mented into the next address location. See
Figure 11. Note
that each data byte is followed by an acknowledge bit.
Read Sequence
Read sequences are comprised of two I
2
C transfer se-
quences. The first is a write sequence that only transfers the
address to be accessed. The second is a read sequence that
starts at the address transferred in the previous address
write access and incrementing to the next address upon
every data byte read. This is shown in
Figure 12.
The write sequence consists of the Start Pulse, the Slave
Device Address including the Read/Write bit (a zero, indicat-
ing a write), then its Acknowledge bit. The next byte is the
address to be accessed, followed by its Acknowledge bit and
the stop bit indicating the end of the address only write
access.
Next the read data access is performed beginning with the
Start Pulse, the Slave Device Address including the Read/
Write bit (a one, indicating a read) and the Acknowledge bit.
The next 8 bits will be the data read from the address
indicated by the write sequence. Subsequent read data
bytes will correspond to the next increment address loca-
tions. Each data byte is separated from the other data bytes
by an Acknowledge bit.
DS200099-31
FIGURE 10. LM126X/LM246X System Neck Board
LM1269
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16
Micro-Controller Interface
(Continued)
DS200099-33
FIGURE 11. I
2
C Write Sequence
DS200099-32
FIGURE 12. I
2
C Read Sequence
LM1269
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17
I
2
C Interface Registers
I
2
C IC ADDRESS
Slave Address of the LM1269 is DCh when writing to the registers and DD when reading from the registers.
LM1269 Pre-Amp Interface Registers (all numbers in Hex)
Register
Ad-
dress
De-
fault
Format
R Gain
Control
00
60h
X
R Gain [6:0]
B Gain
Control
01
60h
X
B Gain [6:0]
G Gain
Control
02
60h
X
G Gain [6:0]
Contrast
Cont.
03
60h
X
Contrast [6:0]
DAC1
04
80h
DAC 1[7:0]
DAC2
05
80h
DAC 2[7:0]
DAC3
06
80h
DAC 3[7:0]
DAC4
07
80h
DAC 4[7:0]
DC Offset/
OSD Cont.
08
15h
X
X
X
OSD_Cont.
[1:0]
DC_Offset [2:0]
Global
Control
09
00h
X
X
O
DCF4
DCF13
O
PS
BV
Increment
Mode
0A
00h
X
X
X
X
X
X
O
INCR
Software
Reset
0F
00h
X
X
X
X
X
X
X
SRST
Pre-Amp Interface Registers
Red Channel Gain Control Register (I
2
C address 00h)
Register name: R Gain Control (00h)
Bit 7
Bit 0
RSV
RG6
RG5
RG4
RG3
RG2
RG1
RG0
Bits 60: Red Channel Gain Control. These seven bits de-
termine the gain for the Red Channel.
Bit 7:
Reserved.
Blue Channel Gain Control Register (I
2
C address 01h)
Register name: B Gain Control (01h)
Bit 7
Bit 0
RSV
BG6
BG5
BG4
BG3
BG2
BG1
BG0
Bits 60: Blue Channel Gain Control. These seven bits
determine the gain for the Blue Channel.
Bit 7:
Reserved.
Green Channel Gain Control Register (I
2
C address 02h)
Register name: G Gain Control (02h)
Bit 7
Bit 0
RSV
GG6
GG5
GG4
GG3
GG2
GG1
GG0
Bits 60: Green Channel Gain Control. These seven bits
determine the gain for the Green Channel.
Bit 7:
Reserved.
Contrast Control Register (I
2
C address 03h)
Register name: Contrast Control (03h)
Bit 7
Bit 0
RSV
CG6
CG5
CG4
CG3
CG2
CG1
CG0
Bits 60: Contrast Control. These seven bits vary the gain
of all three channels.
Bit 7:
Reserved.
DAC Interface Register Definitions
DAC 1 Register (I
2
C address 04h)
Register name: DAC 1 (04h)
Bit 7
Bit 0
D17 D16 D15 D14 D13 D12 D11 D10
Bits 70: DAC 1. These eight bits determine the output
voltage of DAC 1.
DAC 2 Register (I
2
C address 05h)
Register name: DAC 2 (05h)
Bit 7
Bit 0
D27 D26 D25 D24 D23 D22 D21 D20
Bits 70: DAC 2. These eight bits determine the output
voltage of DAC 2.
DAC 3 Register (I
2
C address 06h)
Register name: DAC 3 (06h)
LM1269
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18
DAC Interface Register Definitions
(Continued)
Bit 7
Bit 0
D37 D36 D35 D34 D33 D32 D31 D30
Bits 70: DAC 3. These eight bits determine the output
voltage of DAC 3.
DAC 4 Register (I
2
C address 07h)
Register name: DAC 4 (07h)
Bit 7
Bit 0
D47 D46 D45 D44 D43 D42 D41 D40
Bits 70: DAC 4. These eight bits determine the output
voltage of DAC 4.
DC Offset and OSD Contrast Control Register (I
2
C ad-
dress 08h)
Register name: DC Offset/OSD Cont. (08h)
Bit 7
Bit 0
RSV
RSV
RSV
OSDC1
OSDC0
DC2
DC1
DC0
Bits 20: DC Offset Control. These three bits determine the
active video DC offset to all three channels.
Bits 43: OSD Contrast Control. These two bits determine
the contrast level of the OSD information.
Bits 75: Reserved.
Global Video Control Register (I
2
C address 09h)
Register name: Global Control (09h)
Bit 7
Bit 0
RSV
RSV
0
DCF4
DCF13
0
PS
BV
Bit 0:
Blank Video. When this bit is a one, blank the
video output. When this bit is a zero allow normal
video out.
Bit 1:
Power Save. When this bit is a one, shut down
the analog circuits to support sleep mode. When
this bit is a zero enable the analog circuits for
normal operation.
Bit 2:
MUST BE SET TO "0" FOR PROPER OPERA-
TION.
Bit 3:
DAC13 Configuration. When this bit is a zero
the DAC outputs of DAC13 are full scale
(0V4.5V). When this bit is 1, the range of
DAC13 are halved (0V2.25V).
Bit 4:
DAC4 Configuration. When this bit is a zero the
DAC4 output is not mixed with the other DAC
outputs. When the bit is one, 50% of the DAC4
output is added to DAC13.
Bit 5:
MUST BE SET TO "0" FOR PROPER OPERA-
TION.
Bits 76: Reserved.
Increment Mode Register (I
2
C address 0Ah)
Register name: Increment Mode (0Ah)
Bit 7
Bit 0
RSV
RSV
RSV
RSV
RSV
RSV
TST
INCR
Bit 0:
Increment Enable. When set to a "0", the default
value, the increment mode is enabled. This al-
lows the registers to be updated sequentially by
sending another block of data.
Bit 1:
MUST BE SET TO "0" FOR PROPER OPERA-
TION.
Bits 72: Reserved.
Software Reset Register (I
2
C address 0Fh)
Register name: Software Reset (0Fh)
Bit 7
Bit 0
RSV
RSV
RSV
RSV
RSV
RSV
RSV
SRST
Bit 0:
Software Reset. Setting this bit causes a software
reset. All registers (except this one) are loaded
with their default values. All operations currently
in progress are aborted (except for I
2
C transac-
tions). This bit automatically clears itself when the
reset has been completed.
Bits 71: Reserved.
LM1269
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19
Physical Dimensions
inches (millimeters) unless otherwise noted
LIFE SUPPORT POLICY
NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Email: support@nsc.com
National Semiconductor
Europe
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
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English
Tel: +44 (0) 870 24 0 2171
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Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: ap.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
Order Number LM1269NA
NS Package Number N24D
LM1269
1
1
0
MHz
I
2
C
Compatible
RGB
V
ideo
Amplifier
System
with
OSD
&
DACs
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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