NSC LM1262 200 mhz i2c compatible rgb video amplifier system with osd and dac Datasheet

LM1262
200 MHz I2C Compatible RGB Video Amplifier System
with OSD and DACs
General Description
The LM1262 pre-amp is an integrated CMOS CRT pre-amp.
The IC is I2C compatible, and allows control of all the parameters 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 LM1262 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 preamplifier 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 4 external 8-bit DACs for bus controlled Bias and
Brightness
n Vertical blank from sandcastle or input at pin 13 OR’ed
with horz. blank signal, option selected by I2C
n Contrast and brightness updates synchronous with
vertical blank, enabled by I2C
n Video set to black level through I2C
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 11-lead LM246X driver
Applications
n High end 19” and 21” bus controlled monitors with OSD
n 1600 X 1200, 85 Hz or higher applications
n Low cost and high performance system with LM246X
driver
n I2C compatible interface
Block and Connection Diagram
DS200404-1
FIGURE 1. Order Number LM1262NA
See NS Package Number N24D
© 2002 National Semiconductor Corporation
DS200404
www.national.com
LM1262 200 MHz I2C Compatible RGB Video Amplifier System with OSD and DACs
March 2002
LM1262
Absolute Maximum Ratings (Notes 1, 3)
Thermal Resistance to Case (θJC)
Junction Temperature (TJ)
ESD Susceptibility (Note 4)
ESD Machine Model (Note 5)
Storage Temperature
Lead Temperature
(Soldering, 10 sec.)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage, Pin 9
Peak Video Output Source Current
(Any One Amp)
Pins 18, 19, or 20
Voltage at Any
Input Pin (VIN)
Power Dissipation (PD)
(Above 25˚C Derate based on
θJA and TJ)
Thermal Resistance to Ambient (θJA)
6.0V
28 mA
VCC +0.5 >
VIN > −0.5V
32˚C/W
150˚C
3.5 kV
350V
−65˚C to +150˚C
265˚C
Operating Ratings (Note 2)
Temperature Range
Supply Voltage (VCC)
Video Inputs
2.4W
51˚C/W
0˚C to 70˚C
4.75V < VCC < 5.25V
0.0V < VIN < 1.0Vp-p
Active Video Signal Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Signal Output = 2VP-P.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
230
mA
IS
Maximum Supply Current
Test Setting 1, RL = ∞ (Note
8)
170
IS-PS
Maximum Supply Current,
Power Save Mode
Test Setting 1, RL = ∞, Bit 1 of
Reg. 9 = 1 (Note 8)
45
mA
LE
Linearity Error
Test Setting 4, Triangular
signal input source (Note 9)
5
%
VO Blk Typ
Typical Video Black Level
Output
Test Setting 4, No AC Input
Signal
0.9
1.1
1.3
VDC
VO Blk Step
Video Black Level Step Size
Test Setting 4, No AC Input
Signal
80
110
140
mV
VO White-Max
White Level Video Output
Voltage
Test Setting 3, Video in = 0.7V
4.0
4.3
0
0.05
VBlank
Blanked Output Level
Test Setting 4, AC Input Signal
tr
Rise Time
10% to 90%, Test Setting 4,
AC Input Signal (Note 10)
OSR
Overshoot (Rising Edge)
Test Setting 4, AC Input Signal
(Note 10)
tf
Fall Time
90% to 10%, Test Setting 4,
AC Input Signal (Note 10)
OSF
Overshoot (Falling Edge)
Test Setting 4, AC Input Signal
(Note 10)
f(−3 dB)
Video Amplifier Bandwidth
(Note 13)
Test Setting 4, VO =2VP-P
Vsep 10kHz
Video Amplifier 10 kHz
Isolation
Test Setting 8 (Note 14)
Vsep 10MHz
Video Amplifier 10 MHz
Isolation
Test Setting 8 (Note 14)
V
0.2
V
1.9
ns
6
%
2.0
ns
8
%
200
MHz
−70
dB
−50
dB
AV Max
Maximum Voltage Gain
Test Setting 8, AC Input Signal
AV 1/2
Contrast @ 50% Level
Test Setting 5, AC Input Signal
−10
AV Min
Maximum Contrast Attenuation
Test Setting 2, AC Input Signal
−20
dB
AV Gain 1/2
Gain @ 50% Level
Test Setting 6, AC Input Signal
−5
dB
3.90
4.15
4.40
V/V
dB
AV Gain Min
Maximum Gain Attenuation
Test Setting 7, AC Input Signal
−10
dB
AV Match
Absolute Gain Match @ AV
Test Setting 3, AC Input Signal
± 0.5
dB
AV Track
Gain Change between
Amplifiers
Tracking when changing from
Test Setting 8 to Test Setting 5
(Note 11)
± 0.5
dB
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Max
2
LM1262
Active Video Signal Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Signal Output = 2VP-P.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
VABL TH
ABL Control Upper Limit
Test Setting 4, AC Input Signal
(Note 12)
5
V
VABL Range
ABL Active Range Control
Voltage
Test Setting 4, AC Input Signal
(Note 12)
2.7
V
∆AABL
ABL Control Range
Test Setting 4, AC Input Signal
(Note 12)
−8
dB
IABL Active
ABL Input Bias Current during
ABL
Test Setting 4, AC Input
Signal, VABL = 2V (Note 12)
IABL Max
ABL Input Current Clamp Sink
Capability
VVert Bnk Off
-6
10
µA
Test Setting 4, AC Input Signal
(Note 12)
1
mA
Vertical Blank Gate Low
Input Voltage at pin 13
Vertical Blank Comparators Off
Register B set to 0x02 (Note
18)
1.0
V
Vertical Blank Gate High
Input Voltage at pin 13
Vertical Blank Comparators On
Register B set to 0x02 (Note
18)
IVert Bnk Low
Vertical Blank Gate Low
Input Current at pin 13
V13 = 0V, Register B set to
0x02 (Note 18)
-4.0
µA
IVert Bnk High
Vertical Blank Gate High
Input Current at pin 13
V13 = VCC, Register B set to
0x02 (Note 18)
(internal 50k resistor to ground)
100
µA
VVert Bnk On
0
2.6
VVert Bnk Off
Vertical Blank Gate Low
Input Voltage at pin 23
Vertical Blank Comparators Off
Register B set to 0x06
VVert Bnk On
Vertical Blank Gate High
Input Voltage at pin 23
Vertical Blank Comparators On
Register B set to 0x06 (Note
16)
1.2
VClamp Min
Horizontal Clamp Gate High
Input Voltage
Horizontal Clamp Comparators
On
3.8
V
0.7
V
3.2
V
V
IClamp
Clamp Gate Input Current
V23 = 0V to VCC − 1V,
Register B set to 0x06
−5
tPW Clamp
Back Porch Clamp Pulse Width
(Note 15)
200
ns
tClamp-Video
End of Clamp Pulse to Start of
Active Video
Limit is guaranteed by design
200
ns
tPW SandClamp
Sandcastle Clamp Pulse Width
Horizontal Clamp Comparators
On Register B set to 0x06
(Note 16)
0.1
0.20
10
µA
1.20
µsec
RIn-Video
Input Resistance
Test Setting (4)
VRefOut
VRef Output Voltage
10 kΩ, 1% Resistor; Pin 10 to
GND
1.25
1.40
1.55
V
VSpot
Spot Killer Voltage
VCC Adjusted to Activate
3.4
4.0
4.25
V
20
MΩ
OSD Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Signal Output = 2VP-P, Test Setting 8.
Symbol
Parameter
Conditions
VOSD-L
OSD Input Low Input
Operating Range
OSD Inputs are Selected
VOSD-H
OSD Input High Input
Operating Range
OSD Inputs are Selected
IOSD
OSD Input Current
VOSD = 0V to VCC − 1V
3
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
1.2
V
2.5
−5
V
0.1
10
µA
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LM1262
OSD Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Signal Output = 2VP-P, Test Setting 8.
Symbol
Parameter
Conditions
VOSD-Sel-L
OSD Select Low Input
Operating Range
Video Inputs are Selected
VOSD-Sel-H
OSD Select High Input
Operating Range
OSD Inputs are Selected
IOSD-Sel
OSD Select Input Current
VOSD-Sel = 0V to VCC − 1V
∆VO-OSD(Blk)
OSD ∆Black Level Output
Voltage, Difference from Video
Output
Register 08 = 18, Minimum
Video Black Level
Range of OSD Black Level
Output Voltage between the 3
Channels
Register 08 = 18, Minimum
Video Black Level
OSD Output Voltage, Percent
of Maximum Video Out
VO-OSD(Blk)
VOSD-out
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
1.2
V
3.5
−5
V
0.1
10
µA
± 45
± 150
mV
−100
0
+100
mV
Register 08 = 18, Minimum
Video Black Level
85
95
105
%
52
57
62
%
∆VOSD-out
OSD Output VP-P Attenuation
Register 08 = 08
VOSD-out
(Match)
Output Match between
Channels
Register 08 = 18
VOSD-out
(Track)
Output Variation between
Channels
Register 08 Changed from 18
to 08
± 3.0
∆tOSD/OSD S
Output Skew Time between
OSD and OSD Select
Measured from 50% Point on
all Waveforms
± 2.0
ns
Vfeed 10 kHz
Video Feedthrough into OSD
OSD Inputs = 0V
−70
dB
Vfeed 10 MHz
Video Feedthrough into OSD
OSD Inputs = 0V
−60
dB
± 5.0
%
± 5.0
%
External DAC Signals Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Signal Output = 2VP-P. The following apply for all four external DACs.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
0.5
0.75
V
VMin DAC
Min DAC Output Voltage
Value = 00h
VMax DAC
Mode 00
Max DAC Output Voltage
Value = FFh, DCF[1:0] = 00h
(no load)
3.6
4.2
VMax DAC
Mode 11
Max Output Voltage of DACs
1–3 in DCF Mode 11
Value = FFh, DCF[1:0] = 11h,
DAC4 Value = 00h
2.05
2.40
∆VMax DAC
(Temp)
Variation of any DAC output
voltage with temperature
0˚C < T < 70˚C ambient
∆VMax DAC
(VCC)
Variation of any DAC output
voltage with VCC
4.75V < VCC < 5.25V
Linearity
Linearity of DAC Over its
Range
Monotonicity
Monotonicity of the DAC
Excluding dead zones at limits
of DAC
V
2.75
V
± 0.5
mV/deg
± 50
mV/V
5
%
± 0.5
LSB
External Interface Signals Electrical Characteristics
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Output = 2VP-P.
Symbol
Parameter
2
Vl(I C)
I C Low Input Voltage
SDA or SCL Inputs
Vh(I2C)
I2C High Input Voltage
SDA or SCL Inputs
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2
Conditions
4
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
1.5
3.0
Units
V
V
LM1262
External Interface Signals Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 5 pF, Video Output = 2VP-P.
Symbol
Parameter
Conditions
Min
(Note 7)
Typ
(Note 6)
Max
(Note 7)
Units
tH-Blank on
H-Blank Time Delay from Zero
Crossing Point of H Flyback
Rising Edge of the Flyback
Signal
50
ns
tH-Blank off
H-Blank Time Delay from Zero
Crossing Point of H Flyback
Falling Edge of the Flyback
Signal
50
ns
IIn Threshold
IIn H-Blank Detection
Threshold
−20
µA
IIn-Operating
Minimum — Insure Normal
Operation
Maximum — Should Not
Exceed in Normal Operation
Lowest Operating Horizontal
Frequency in Given Application
(Note 17)
Peak Current during Flyback
Period, Recommended Design
Range
Operating Range for all
Horizontal Scan Frequencies,
Maximum Current Should Not
Exceed 2 mA (Note 17)
IIn Flyback
−30
0.5
1.5
−300
µA
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.
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 kΩ 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 50Ω).
Note 6: Typical specifications are specified at +25˚C 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 VCC with RL = ∞. 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 VP-P level at the input, subdivided into 16 equal steps,
with each step approximately 100 ns in width.
Note 10: Input from signal generator: tr, tf < 1 ns. Scope and generator response used for testing: tr = 1.1 ns, tf = 0.9 ns. Using the RSS technique the scope and
generator response have been removed from the output rise and fall times.
Note 11: ∆AV 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 AV 1/2 and measured relative to the AV max condition. For example, at AV 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 AV 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
∆AABL = A(VABL = VABL Max
Gain)
- A(VABL = VABL 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 (AV 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 fIN = 10 MHz for Vsep 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 internal circuit detects the vertical blank only when this signal is present in the sandcastle input. There is typically an 800 nsec delay in detecting the
vertical blank signal. If only the horizontal clamp is present the vertical blank will not be activated. Rise and fall times of the sandcastle input signal should be 10 nsec
or faster.
Note 17: Limits met by matching the external resistor going to pin 24 to the H Flyback voltage.
Note 18: A 4.7 kΩ resistor must be in series with pin 13 when this pin is the input for vertical blanking. When the LM1262 is first turned on the default condition for
pin 13 is for the DAC4 output. Under this condition pin 13 will be damaged by the vertical blanking input if a series resistor is not used.
5
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LM1262
Typical Performance Characteristics
VCC = 5V, TA = 25˚C unless otherwise specified.
Gain Attenuation
Contrast Attenuation
DS200404-2
ABL Attenuation
DS200404-3
Rise and Fall
DS200404-5
DS200404-4
Contrast vs Frequency
Gain vs Frequency
DS200404-6
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DS200404-7
6
LM1262
Test Circuit
DS200404-10
Note: 5pF load includes parasitic capacitance.
Test Settings
Control
No.
Basic
Basic
Basic
of
Test
Test
Test
Bits Setting 1 Setting 2 Setting 3
Basic
Test
Setting 4
Basic
Basic
Basic
Basic
Test
Test
Test
Test
Setting 5 Setting 6 Setting 7 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
2VP-P
Max
(Hex 7F)
50%
(Hex 40)
Min
(Hex 00)
Max
(Hex 7F)
Video DC Offset & OSD Cont.
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
DS200404-11
FIGURE 2. Blanking Propagation Delay
7
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LM1262
Timing Diagrams
(Continued)
DS200404-12
FIGURE 3. OSD Output Skew
Pin Descriptions
Pin No.
Pin Name
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.
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Schematic
Description
8
LM1262
Pin Descriptions
(Continued)
Pin No.
Pin Name
5
6
7
Red Video In
Green Video In
Blue Video In
Schematic
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 Ω and external ESD protection
diodes should also be used for ESD
protection.
Description
8
Analog Ground
Ground Pin for the analog circuits of the
LM1262.
9
VCC
Power supply pin for LM1262.
10
VrefRext
Sets the internal current sources through a
10 kΩ 1% external resistor. Resistor value
and accuracy is critical for optimum
operation of the LM1262.
11
SDA
The I2C data line. A pull-up resistor of about
2 kΩ should be connected between this pin
and +5V. A 300 Ω resistor should be
connected in series with the data line for
protection against arcing.
12
SCL
The I2C Clock line. A pull-up resistor of
about 2 kΩ should be connected between
this pin and +5V. A 300 Ω 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 I2C bus.
17
Digital Ground
Ground Pin for the digital circuits of the
LM1262.
9
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LM1262
Pin Descriptions
(Continued)
Pin No.
Pin Name
18
19
20
Blue Video Out
Green Video Out
Red Video Out
Video outputs of the LM1262. 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
VRef Out
A 0.1 µF capacitor must be placed close to
this pin for decoupling the internal VRef. 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. The signal can be either positive or
negative going. The polarity is set in register
0Bh bit-3. The 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 LM1262 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.
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Schematic
Description
10
All functions of the LM1262 are controlled through the I2C
Bus. Details on the internal registers are covered in the
I2C Interface Registers Section. Figure 1 shows the block
diagram of the LM1262. The I2C signals come in on pins
11 and 12 and go to the I2C Interface. Both the internal
blocks with an “R” and the four external DACs are controlled by the I2C 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; however, they are identical to the red channel.
Proper operation of the LM1262 does require a very
accurate reference voltage. This voltage is generated in
the VRef block. To insure an accurate voltage over temperature, an external resistor is used to set the current in
the VRef 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 VRef stage goes to a number of blocks in the
video section and also to pin 21. This pin allows capacitor
filtering on the VRef output and offers an accurate external
reference. A buffer must be used with this reference, the
maximum current loading should be only 100 µA.
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:
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
LM1262.
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 LM1262, the coupling cap is also used to store the
reference voltage for DC restoration. The “Clamp DC Restore 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 processing. Input impedance to this stage is typically 20 MΩ.
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 I2C 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 attenuation. 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 attenuation 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
Where:
VS is the external supply (usually the CRT driver supply rail,
about 80V)
VABL TH is the threshold ABL voltage of the IC
RABL is the ABL resistor value
IABL 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 IABL.
11
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LM1262
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.
Functional Description
LM1262
Functional Description
(Continued)
DS200404-26
FIGURE 4. ABL
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 horizontal 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.
RLIMIT is used to limit the input current into the IC to a typical
value of +1 mA during flyback and −100 µA during normal
forward scan. For example if an H flyback with a peak of
100V is used, RLIMIT = 100 kΩ. 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 RLIMIT. A
56 pF capacitor has been added to the H Flyback pin on the
demo board for filtering noise on the H Flyback signal.
DS200404-27
FIGURE 5. H Flyback Input Pulse
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.
DS200404-28
FIGURE 6. Standard Logic H Blank
V Blank and Sandcastle Pulse: By setting bit 1 of register
0B to a “1” the vertical blanking function is enabled. In this
mode the vertical blanking is OD’d with the horizontal blanking, setting the outputs of the LM1262 to the blank level the
vertical flyback time. Activating vertical blanking also synchronizes the I2C updates being made to the contrast and
DAC4 (brightness) registers to occur within the vertical retrace period. Therefore each field will have a uniform brightness since all contrast and brightness changes occur only
during the vertical retrace period.
Two different ways are used to input vertical blanking into the
LM1262:
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12
ity of the LM1262 is 3.5 kV, however many monitor manufacturers 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 LM1262 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
LM1262. This provides the best protection against ESD.
When this protection is combined with good PCB layout the
LM1262 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 LM1262 also provide good protection
against arc-over, however good PCB layout is necessary.
The LM1262 should not be exposed directly to the voltages
that may occur during arc-over. The main vulnerability of the
LM1262 to arc-over is though the ground traces on the PCB.
For proper protection all ground connections associated with
the LM1262, 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 LM1262
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:
(Continued)
1.
A logic level vertical blanking pulse comes in at pin 13.
Bit 2 of register 0B is set to a “0” to enable this method.
There is no output for DAC4, but its output is still connected to DAC1-3 inputs, maintaining the brightness
feature. WARNING: A 4.7 kΩ resistor must be in series
with pin 13 when it is used for the vertical blanking input,
see Note 18.
2. A sandcastle pulse comes in at pin 23. Bit 2 of register
0B is set to a “1”, the default value. Vertical blanking is
detected from the sandcastle pulse. Note that bit 1 of
register 0B must also be set to a “1” for proper detection
of the sandcastle pulse. The output of DAC4 is connected to pin 13 as well as DAC1-3. The sandcastle
detection is compatible with the sandcastle pulse generated by the Philips defection controller parts.
Power Save Mode: There are two modes of power save:
1. Blanking the video
2. Turning off most of the power for maximum power savings.
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
LM1262, 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 LM1262
is a CMOS device its power consumption will be minimal.
External DACs: Four DACs with external outputs are provided in the LM1262. Normally these DACs will be used for
color balance and brightness control. If the brightness control 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 cathodes. DAC 4 can be set to vary the outputs of the other three
DACs after the color balance is completed. This is accomplished 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 1–3 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 1–3 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.
When the brightness control is done at the cathodes and the
output of DAC 4 is not used, then pin 13 can be used as a
vertical input. This function is controlled by bit 2 in register B.
•
All grounds associated with the LM1262 should be connected 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 LM1262 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 LM1262 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
LM1262 may become more vulnerable to arc-over. Improper
grounding is by far the most common cause of video preamp failures during arc-over.
ESD and Arc-Over Protection
The LM1262 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-
DS200404-29
FIGURE 7. Recommended Video Input ESD Protection
13
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LM1262
Functional Description
LM1262
Schematic
DS200404-35
FIGURE 8. High Speed Low Cost Neck Board Schematic
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14
LM1262
Schematic
(Continued)
DS200404-36
FIGURE 9. High Speed Low Cost Neck Board Schematic
15
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LM1262
PCB Layout
DS200404-37
FIGURE 10. High Speed Low Cost System Neck Board
Read Sequence
Read sequences are comprised of two I2C transfer sequences. 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, indicating 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 locations. Each data byte is separated from the other data bytes
by an Acknowledge bit.
Micro-Controller Interface
The micro-controller interfaces to the LM1262 pre-amp via
an I2C 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 LM1262 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
I2C 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 (7–1) 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
LM1262 is set for the increment mode. In this mode when
more than one data byte is sent it is automatically incremented into the next address location. See Figure 11. Note
that each data byte is followed by an acknowledge bit.
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16
LM1262
Micro-Controller Interface
(Continued)
DS200404-33
2
FIGURE 11. I C Write Sequence
DS200404-32
FIGURE 12. I2C Read Sequence
17
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LM1262
I2C Interface Registers
I2C IC ADDRESS
Slave Address of the LM1262 is DCh when writing to the registers and DD when reading from the registers.
LM1262 Pre-Amp Interface Registers (all numbers in Hex)
Register
Address
Default
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
DC Offset/
OSD Cont.
08
15h
X
X
X
Global
Control
09
00h
X
X
O
DCF4
Increment
Mode
0A
00h
X
X
X
X
VBL/00R
0B
04h
X
X
X
Software
Reset
0F
00h
X
X
X
DAC 4[7:0]
Pre-Amp Interface Registers
RSV
RG5
RG4
RG3
RG2
RG1
RSV
RG0
BG5
BG4
BG3
BG2
BG1
GG5
GG4
GG3
GG2
GG1
INCR
X
CLMP
DAC4
VBL
00R
X
X
X
X
SRST
Bit 0
CG6
CG5
CG4
CG3
CG2
CG1
CG0
Bit 0
DAC 2 Register (I2C address 05h)
Register name: DAC 2 (05h)
Bit 7
Bit 0
D2–7 D2–6 D2–5 D2–4 D2–3 D2–2 D2–1 D2–0
GG0
Bits 7–0: DAC 2. These eight bits determine the output
voltage of DAC 2.
Bits 6–0: Green Channel Gain Control. These seven bits
determine the gain for the Green Channel.
Bit 7:
Reserved.
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O
Bits 7–0: DAC 1. These eight bits determine the output
voltage of DAC 1.
Bit 0
GG6
X
D1–7 D1–6 D1–5 D1–4 D1–3 D1–2 D1–1 D1–0
Green Channel Gain Control Register (I2C address 02h)
Register name: G Gain Control (02h)
RSV
X
Bit 7
BG0
Bits 6–0: Blue Channel Gain Control. These seven bits
determine the gain for the Blue Channel.
Bit 7:
Reserved.
Bit 7
BV
DAC 1 Register (I2C address 04h)
Register name: DAC 1 (04h)
Bit 0
BG6
PS
DAC Interface Register Definitions
Blue Channel Gain Control Register (I2C address 01h)
Register name: B Gain Control (01h)
RSV
O
Bits 6–0: Contrast Control. These seven bits vary the gain
of all three channels.
Bit 7:
Reserved.
Bits 6–0: Red Channel Gain Control. These seven bits determine the gain for the Red Channel.
Bit 7:
Reserved.
Bit 7
DCF1–3
Bit 7
Bit 0
RG6
DC_Offset [2:0]
Contrast Control Register (I2C address 03h)
Register name: Contrast Control (03h)
Red Channel Gain Control Register (I2C address 00h)
Register name: R Gain Control (00h)
Bit 7
OSD_Cont.
[1:0]
18
Register name: Increment Mode (0Ah)
(Continued)
DAC 3 Register (I2C address 06h)
Bit 7
Register name: DAC 3 (06h)
RSV
Bit 7
DAC 4 Register (I2C address 07h)
Register name: DAC 4 (07h)
D4–7 D4–6 D4–5 D4–4 D4–3 D4–2 D4–1 D4–0
Bits 7–0: DAC 4. These eight bits determine the output
voltage of DAC 4.
DC0
Global Video Control Register (I2C address 09h)
Register name: Global Control (09h)
Bit 0
RSV
0
DCF4
DCF1–3
0
PS
0
INCR
Bit 0
RSV
RSV
RSV
CLMP
DAC4
VBL
OOR
OSD Only Register: When this bit is 0 (default)
normal video operation is assumed. When this bit
is 1, the video is blanked, only the OSD window is
displayed (used for “out-of-range” condition).
Bit 1:
Vertical Blank Enable: When this bit is set to 1 the
vertical blanking pulse is OR’d with the horizontal
blank pulse at the preamplifier output, to blank
the video during both the vertical and horizontal
retrace. I2C changes for contrast and DAC4 will
only be updated during vertical retrace period.
When this bit is set to 0 (default) the internal
vertical blanking is disabled (horizontal blanking
is not affected) and I2C changes for contrast and
DAC4 occur anytime in the video field. NOTE: If
there is no vertical signal to the LM1262, this bit
must be set to a 0 for proper operation.
Bit 2:
DAC4 I/O Switch: When this bit is set to 1 (default) DAC4 output is enabled. When this bit is set
to a 0 the DAC4 output is disabled and pin 13 is
used for the vertical blank input. DAC4 can still be
connected internally to DAC1-3. When both bits 1
and 2 are set to 1 vertical blanking will be stripped
from the sandcastle pulse at pin 23. For proper
detection of the sandcastle pulse the CLMP bit
(bit 3) must be set to a 0, positive polarity for the
clamp input.
Bit 3:
Determines the polarity of the clamp signal used
by the LM1262, “0” (default) is a positive clamp
signal, “1” is a negative going clamp signal.
Bits 7–4: Reserved.
Bits 2–0: DC Offset Control. These three bits determine the
active video DC offset to all three channels.
Bits 4–3: OSD Contrast Control. These two bits determine
the contrast level of the digital OSD information.
Bits 7–5: Reserved.
Bit 7
RSV
Bit 0:
DC Offset and OSD Contrast Control Register (I2C address 08h)
Register name: DC Offset/OSD Cont. (08h)
Bit 0
RSV
Bit 7
RSV
RSV RSV RSV OSDC1 OSDC0 DC2 DC1
RSV
Clamp Polarity, Vertical Blanking, and OSD Control (I2C
address 0Bh)
Register name: Clamp/VBL/OOR (0Bh)
Bit 0
Bit 7
RSV
Increment Enable. When set to a “0”, the default
value, the increment mode is enabled. This allows the registers to be updated sequentially by
sending another block of data.
Bit 1:
MUST BE SET TO “0” FOR PROPER OPERATION.
Bits 7–2: Reserved.
D3–7 D3–6 D3–5 D3–4 D3–3 D3–2 D3–1 D3–0
Bit 7
Bit 0
RSV
Bit 0:
Bit 0
Bits 7–0: DAC 3. These eight bits determine the output
voltage of DAC 3.
RSV
LM1262
Increment Mode Register (I2C address 0Ah)
DAC Interface Register Definitions
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 OPERATION.
Bit 3:
DAC1–3 Configuration. When this bit is a zero
the DAC outputs of DAC1–3 are full scale
(0V–4.5V). When this bit is 1, the range of
DAC1–3 are halved (0V–2.25V).
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 DAC1–3.
Bit 5:
MUST BE SET TO “0” FOR PROPER OPERATION.
Bits 7–6: Reserved.
Software Reset Register (I2C address 0Fh)
Register name: Software Reset (0Fh)
Bit 7
RSV
Bit 0
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 I2C transactions). This bit automatically clears itself when the
reset has been completed.
Bits 7–1: Reserved.
19
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LM1262 200 MHz I2C Compatible RGB Video Amplifier System with OSD and DACs
Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number LM1262NA
NS Package Number N24D
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