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LM1267 150 MHz I2C RGB Video Amplifier System with OSD and DACs
October 2000
LM1267 150 MHz I2C RGB Video Amplifier System with OSD and DACs
General Description
The LM1267 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 LM1267 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 the additional black level clamp capacitors. The IC is packaged in an industry standard 24-lead DIP molded plastic package. n Programmable 110 MHz to 150 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 15 and 17 bus controlled monitors with OSD n 1024 X 768 displays up to 85 Hz requiring OSD capability n Very low cost system with LM246X driver
Features
n I2C compatible interface
Block and Connection Diagram
DS200050-1
FIGURE 1. Order Number LM1267N See NS Package Number N24N
(c) 2000 National Semiconductor Corporation
DS200050
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LM1267
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 Peak Video Output Source Current (Any One Amp) Pins 18, 19 or 20 Voltage at Any Input Pin (VIN) Power Dissipation (PD) (Above 25C Derate based on JA and TJ) Thermal Resistance to Ambient (JA) 6.0V
Thermal Resistance to Case (JC) Junction Temperature (TJ) ESD Susceptibility (Note 4) ESD Machine Model (Note 5) Storage Temperature Lead Temperature (Soldering, 10 sec.)
32C/W 150C 3.5 kV 350V -65C to +150C 265C
28 mA VCC +0.5 > VIN > -0.5V
Operating Ratings (Note 2)
Temperature Range Supply Voltage (VCC) Video Inputs 0C to 70C 4.75V < VCC < 5.25V 0.0V < VIN < 1.2V
2.4W 51C/W
Active Video Signal Electrical Characteristics
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Output = 3.5 VP-P. Symbol IS IS-PS LE VO Blk Typ Parameter Maximum Supply Current Maximum Supply Current, Power Save Mode Linearity Error Typical Video Black Level Output Video Black Level Step Size Variation in Output Video Black Level vs VCC Variations White Level Video Output Voltage Blanked Output Level Rise Time Overshoot (Rising Edge) Fall Time Overshoot (Falling Edge) Video Amplifier Bandwidth (Note 13) Video Amplifier 10 kHz Isolation Video Amplifier 10 MHz Isolation Maximum Voltage Gain Contrast @ 50% Level Maximum Contrast Attenuation
1
Conditions Test Setting 1, RL = (Note 8) Test Setting 1, RL = , Bit 1 of Reg. 9 = 1 (Note 8) Test Setting 4, Triangular signal input source (Note 9) Test Setting 4, No AC Input Signal, DC = 5 Hex, or 0.5V Offset Test Setting 4, No AC Input Signal Test Setting 1 & 3, No AC Input Signal, 4.75 < VCC < 5.25 Test Setting 3, Video in = 0.7V Test Setting 4, AC Input Signal 10% to 90%, Test Setting 4, AC Input Signal (Note 10) Test Setting 4, AC Input Signal (Note 10) 10% to 90%, Test Setting 4, AC Input Signal (Note 10) Test Setting 4, AC Input Signal (Note 10) Test Setting 8, Register 0Bh Bits 2-0 Set to 111, VO = 3.5 VP-P Test Setting 8 (Note 14) Test Setting 8 (Note 14) Test Setting 8, AC Input Signal Test Setting 5, AC Input Signal Test Setting 2, AC Input Signal Test Setting 6, AC Input Signal Test Setting 7, AC Input Signal Test Setting 3, AC Input Signal
Min (Note 7)
Typ (Note 6) 220 45 5
Max (Note 7) 245 60
Units mA mA %
1.05
1.25
1.45
VDC
VO Blk Step VO/VCC VO White-Max VBlank tr OSR tf OSF f(-3 dB)
60 -50 4.0 0
90 0 4.2 0.2 3.0 8 3.0 8
120 50
mV mV/V V
0.5
V ns % ns %
150
MHz
Vsep 10 kHz Vsep 10 MHz AV Max AV
1
-70 -50 4 -10 -20 -5 -10
dB dB V/V dB dB dB dB dB
2
AV Min AV Gain
2
Gain @ 50% Level Maximum Gain Attenuation Absolute Gain Match @ AVmax
AV Gain Min AV Match
0.5
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LM1267
Active Video Signal Electrical Characteristics
Symbol AV Track Parameter Gain Change between Amplifiers ABL Control Upper Limit ABL Control Voltage Active Range ABL Control Range ABL Input Bias Current during ABL ABL Input Current Clamp Sink Capability Clamp Gate Low Input Voltage Clamp Gate High Input Voltage Clamp Gate Input Current Back Porch Clamp Pulse Width End of Clamp Pulse to Start of Active Video Input Resistance Input Bias Current VRef Output Voltage Spot Killer Voltage Conditions
(Continued)
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Output = 3.5 VP-P. Min (Note 7) Typ (Note 6) Max (Note 7) Units
Tracking when Changing from Test Setting 8 to Test Setting 5 (Note 11) Test Setting 4, AC Input Signal (Note 12) Test Setting 4, AC Input Signal (Note 12) Test Setting 4, AC Input Signal (Note 12) Test Setting 4, AC Input Signal, VABL = 2V(Note 12) Test Setting 4, AC Input Signal (Note 12) Clamp Comparators Off Clamp Comparators On V23 = 0V to VCC - 1V (Note 15) Limit is guaranteed by design Test Setting (4) Test Setting (4) 10 k, 1% Resistor; Pin 10 to GND VCC Adjusted to Activate 1.25 3.75 2.6 -5 200 200
0.5
5 2 -10 0 10 1 1.4 0.1 10
dB
VABL TH VABL Range AABL IABL Active IABL Max VClamp Max VClamp Min IClamp tPW Clamp tClamp-Video Rin-Video Iin-Video VRefOut VSpot
V V dB A mA V V A ns nsec
20 0.1 1.40 4.0 10 1.55 4.25
M A V V
OSD Electrical Characteristics
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Signal Output = 3.5 VP-P, Test Setting 8. Symbol VOSD-L VOSD-H IOSD VOSD-Sel-L VOSD-Sel-H IOSD-Sel VO-OSD(Blk) Parameter OSD Input Low Input Operating Range OSD Input High Input Operating Range OSD Input Current OSD Select Low Input Operating Range OSD Select High Input Operating Range OSD Select Input Current OSD Black Level Output Voltage, Difference from Video Output Range of OSD Black Level Output Voltage between the 3 Channels OSD Output Voltage, Percent of Maximum Video Out OSD Output VP-P Attenuation Output Variation between Channels Conditions OSD Inputs are Selected OSD Inputs are Selected VOSD = 0V to VCC - 1V Video Inputs are Selected OSD Inputs are Selected VOSD-Sel = 0V to VCC - 1V Register 08=18, Minimum Video Black Level Register 08=18, Minimum Video Black Level Register 08 = 08, Minimum Video Black Level Register 08 = 08 Register 08 Changed from 18 to 08
3
Min (Note 7)
Typ (Note 6)
Max (Note 7) 1.2
Units V V
2.5 -5 0.1 10 1.2 2.5 -5 0.1 10
A V V A mV
45
150
VO-OSD(Blk)
-100
0
+100
mV
VOSD-out VOSD-out VOSD-out (Track)
69 55
79 60
89 65
% % %
3.0
5.0
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LM1267
OSD Electrical Characteristics
(Continued)
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Signal Output = 3.5 VP-P, Test Setting 8. Symbol tOSD/OSD S Vfeed 10 kHz Vfeed 10 MHz Parameter Output Skew Time between OSD and OSD Select Video Feedthrough into OSD Video Feedthrough into OSD Conditions Measured from 50% Point on all Waveforms OSD Inputs = 0V OSD Inputs = 0V Min (Note 7) Typ (Note 6) Max (Note 7) Units ns dB dB
2.0
-70 -60
External DAC Signals Electrical Characteristics
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Signal Output = 3.5 VP-P. The following apply for all four external DACS. Symbol VMin DAC VMax DAC Mode 00 VMax DAC Mode 11 VMax DAC (Temp) VMax DAC (VCC) Linearity Monotonicity Parameter Min DAC Output Voltage Max DAC Output Voltage Max Output Voltage of DACs 1-3 in DCF Mode 11 Variation of any DAC output voltage with temperature Variation of any DAC output voltage with VCC Linearity of DAC Over its Range Monotonicity of the DAC Excluding dead zones at limits of DAC Conditions Value = 00h Value = FFh, DCF[1:0]=00h (no load) Value = FFh, DCF[1:0]=11h, DAC4 Value = 00h 0C < T < 70C ambient 4.75V < VCC < 5.25V 3.7 1.85 Min (Note 7) Typ (Note 6) 0.5 4.2 2.1 2.35 Max (Note 7) 0.65 Units V V V mV/deg mV/V % LSB
0.5 50
5
0.5
External Interface Signals Electrical Characteristics
Unless otherwise noted: TA = 25C, VCC = +5V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Output = 3.5 VP-P. Symbol Vl(I2C) Vh(I C) Il(I C) Ih(I2C) tH-Blank on tBlank off IInThreshold IIn-Operating
2 2
Parameter I2C Low Input Voltage I2C High Input Voltage I C Low Input Current I2C High Input Current H-Blank Time Delay from Zero Crossing Point of H Flyback H-Blank Time Delay from Zero Crossing Point of H Flyback IIn H-Blank Detection Threshold Minimum -- Insure Normal Operation Maximum -- Should Not Exceed in Normal Operation Peak Current during Flyback Period, Recommended Design Range
2
Conditions SDA or SCL Inputs SDA or SCL Inputs SDA or SCL Inputs, Input Voltage = 0V SDA or SCL Inputs, Input Voltage = 5V Rising Edge of the Flyback Signal Falling Edge of the Flyback Signal
Min (Note 7) -0.5 3.0 1.9 0.3
Typ (Note 6) 0.5 4.0 2.2 0.6 50 50 -20
Max (Note 7) 1.5 5.0 2.5 0.9
Units V V A A ns ns A
Lowest Operating Horizontal Frequency in Given Application
-30
-300
A
IIn Flyback
Operating Range for all Horizontal Scan Frequencies, Maximum Current Should Not Exceed 2 mA
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.
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LM1267
External Interface Signals Electrical Characteristics
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.
(Continued)
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 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.
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 12 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 12. This yields a typical gain change of 10.0 dB with the tracking change of 0.2 dB. Note 12: ABL should provide smooth decrease in gain over the operational range of 0 dB to -5 dB
AABL = A(VABL = VABL Max
Gain)
-- A(VABL = VABL Min
Gain)
Beyond -5 dB the gain characteristics, linearity and pulse response 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 video black level is used for this test. OSD amplitude is measured from the video black level to the OSD white level.
Typical Performance Characteristics
Gain Attenuation
VCC = 5V, TA = 25 unless otherwise specified. Contrast Attenuation
DS200050-2
DS200050-3
ABL Attenuation
Output Waveform
DS200050-5
DS200050-4
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LM1267
Typical Performance Characteristics
Contrast vs Frequency, Bandwidth = 0
VCC = 5V, TA = 25 unless otherwise specified. (Continued) Contrast vs Frequency, Bandwidth = 7
DS200050-6
DS200050-7
Gain vs Frequency, Bandwidth = 0
Gain vs Frequency, Bandwidth = 7
DS200050-8
DS200050-9
Test Circuit
DS200050-10
Note: 8 pF load includes parasitic capacitance.
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LM1267
Test Settings
Control Contrast R, G, B Gain No. of Bits 7 7 Basic Test Setting 1 Max (Hex 7F) Max (Hex 7F) Min (Hex 10) Basic Test Setting 2 Min (Hex 00) Max (Hex 7F) 0.5V (Hex 15) Basic Test Setting 3 Max (Hex 7F) Max (Hex 7F) Max (Hex 17) Basic Test Setting 4 Max (Hex 7F) Set Video Output to 2VP-P 0.5V (Hex 15) Basic Test Setting 5 50% (Hex 40) Max (Hex 7F) 0.5V (Hex 15) Basic Test Setting 6 Max (Hex 7F) 50% (Hex 40) 0.5V (Hex 15) Basic Test Setting 7 Max (Hex 7F) Min (Hex 00) 0.5V (Hex 15) Basic Test Setting 8 Max (Hex 7F) Max (Hex 7F) 0.5V (Hex 15)
Video DC Offset
3
Timing Diagrams
DS200050-11
FIGURE 2. Blanking Propagation Delay
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LM1267
Timing Diagrams
(Continued)
DS200050-12
FIGURE 3. OSD Output Skew
Pin Descriptions
Pin No. 1 2 3 Pin Name Red OSD Input Green OSD Input Blue OSD Input Schematic Description 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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LM1267
Pin Descriptions
Pin No. 5 6 7 Pin Name Red Video In Green Video In Blue Video In
(Continued) Schematic Description Video inputs. These inputs must be AC coupled with a 0.047 F 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 9 10
Analog Ground VCC VrefRext
Ground Pin for the analog circuits of the LM1267. Power supply pin for LM1267. Sets the internal current sources through a 10 k 1% external resistor. Resistor value and accuracy is critical for optimum operation of the LM1267.
11
SDA
The I2C 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 I2C 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 I2C bus.
17
Digital Ground
Ground Pin for the digital circuits of the LM1267.
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LM1267
Pin Descriptions
Pin No. 18 19 20 Pin Name
(Continued) Schematic Description Video outputs of the LM1267. The ideal driver for this part is the LM246X CRT driver family, which has the necessary gain of 26 dB or 20 V/V.
Blue Video Out Green Video Out Red Video Out
21
VRef Out
A 0.1 F 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. H flyback is an analog signal input from the monitor horizontal scan. The LM1267 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.
24
H Flyback
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LM1267
Functional Description
All functions of the LM1267 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 LM1267. 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 LM1267 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 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 LM1267.
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:
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 LM1267, 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 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 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.
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LM1267
Functional Description
(Continued)
DS200050-26
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 of 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 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, RLIMIT = 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 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.
DS200050-27
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.
DS200050-28
FIGURE 6. Standard Logic H Blank 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
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LM1267
Functional Description
(Continued)
LM1267, 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 LM1267 is a CMOS device its power consumption will be minimal.
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 LM1267 also provide good protection against arc-over, however good PCB layout is necessary. The LM1267 should not be exposed directly to the voltages that may occur during arc-over. The main vulnerability of the LM1267 to arc-over is though the ground traces on the PCB. For proper protection all ground connections associated with the LM1267, 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 LM1267 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:
External DACs: Four DACs with external outputs are provided in the LM1267. 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 ouput 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.
* * *
All grounds associated with the LM1267 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 LM1267 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.
*
ESD and Arc-Over Protection
The LM1267 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 susceptibility of the LM1267 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 LM1267 provides excellent protection against both ESD and arc-over, but this is not a substitute for good PCB layout.
Output signal traces of the LM1267 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 LM1267 may become more vulnerable to arc-over. Improper grounding is by far the most common cause of video preamp failure during arc-over.
*
Figure 7 shows the recommended input protection for the LM1267. This provides the best protection against ESD. When this protection is combined with good PCB layout the LM1267 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
DS200050-29
FIGURE 7. Recommended Video Input ESD Protection
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LM1267
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DS200050-30
Schematic
14
FIGURE 8. LM126X/LM246X Neck Board Schematic
Schematic
(Continued)
LM1267
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DS200050-34
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FIGURE 9. LM126X/LM246X Neck Board Schematic
LM1267
PCB Layout
DS200050-31
FIGURE 10. LM126X/LM246X System Neck Board
Micro-Controller Interface
The micro-controller interfaces to the LM1267 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 LM1267 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
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LM1267
Micro-Controller Interface
(Continued)
LM1267 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. 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, 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 locations. Each data byte is separated from the other data bytes by an Acknowledge bit.
DS200050-33
FIGURE 11. I2C Write Sequence
DS200050-32
FIGURE 12. I C Read Sequence
2
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LM1267
I2C Interface Registers
I2C IC ADDRESS Slave Address of the LM1267 is DCh when writing to the registers and DD when reading from the registers. LM1267 Pre-Amp Interface Registers (all numbers in Hex) Register R Gain Control B Gain Control G Gain Control Contrast Cont. DAC1 DAC2 DAC3 DAC4 DC Offset/ OSD Cont. Global Control Increment Mode Clamp/BW Software Reset Address 00 01 02 03 04 05 06 07 08 09 0A 0B 0F Default 60h 60h 60h 60h 80h 80h 80h 80h 15h 00h 00h 04h 00h X X X X X X X X X X X O X X X X X X X Format R Gain [6:0] B Gain [6:0] G Gain [6:0] Contrast [6:0] DAC 1[7:0] DAC 2[7:0] DAC 3[7:0] DAC 4[7:0] OSD_Cont. [1:0] DCF4 X X X DCF1-3 X CLMP X X O X DC_Offset [2:0] PS O BV INCR
BANDWIDTH[2:0] X SRST
Pre-Amp Interface Registers
Red Channel Gain Control Register (I2C address 00h) Register name: R Gain Control (00h) Bit 7 RSV RG6 RG5 RG4 RG3 RG2 RG1 Bit 0 RG0
Contrast Control Register (I2C address 03h) Register name: Contrast Control (03h) Bit 7 RSV CG6 CG5 CG4 CG3 CG2 CG1 Bit 0 CG0
Bits 6-0: Red Channel Gain Control. These seven bits determine the gain for the Red Channel. Bit 7: Reserved. Blue Channel Gain Control Register (I2C address 01h) Register name: B Gain Control (01h) Bit 7 RSV BG6 BG5 BG4 BG3 BG2 BG1 Bit 0 BG0
Bits 6-0: Contrast Control. These seven bits vary the gain of all three channels. Bit 7: Reserved.
DAC Interface Register Definitions
DAC 1 Register (I2C address 04h) Register name: DAC 1 (04h) Bit 7 Bit 0
Bits 6-0: Blue Channel Gain Control. These seven bits determine the gain for the Blue Channel. Bit 7: Reserved. Green Channel Gain Control Register (I2C address 02h) Register name: G Gain Control (02h) Bit 7 RSV GG6 GG5 GG4 GG3 GG2 GG1 Bit 0 GG0
D1-7 D1-6 D1-5 D1-4 D1-3 D1-2 D1-1 D1-0 Bits 7-0: DAC 1. These eight bits determine the output voltage of DAC 1. 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 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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LM1267
DAC Interface Register Definitions
(Continued) DAC 3 Register (I2C address 06h) Register name: DAC 3 (06h) Bit 7 Bit 0
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.
MUST BE SET TO "0" FOR PROPER OPERATION. Bits 7-6: Reserved Increment Mode Register (I2C address 0Ah) Register name: Increment Mode (0Ah) Bit 7 RSV RSV RSV RSV RSV RSV TST Bit 0: Bit 0 INCR
Bit 5:
D3-7 D3-6 D3-5 D3-4 D3-3 D3-2 D3-1 D3-0 Bits 7-0: DAC 3. These eight bits determine the output voltage of DAC 3. DAC 4 Register (I2C address 07h) Register name: DAC 4 (07h) Bit 7 Bit 0
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. DC Offset and OSD Contrast Control Register (I2C address 08h) Register name: DC Offset/OSD Cont. (08h) Bit 7 RSV RSV RSV OSDC1 OSDC0 DC2 DC1 Bit 0 DC0
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 Clamp Polarity and Bandwidth (I2C address 0Bh) Register name: Clamp/BW (0Bh) Bit 7 RSV RSV RSV RSV CLMP BW1 BW2 Bit 0 BW0
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. Global Video Control Register (I2C address 09h) Register name: Global Control (09h) Bit 7 RSV Bit 0: RSV O DCF4 DCF1-3 O PS Bit 0 BV Blank Video. When this bit is a one, blank the video output. When this bit is a zero allow normal video out. Power Save. When this bit is one, shut down the analog circuits to support sleep mode. When this bit is a zero enable the analog circuits for normal operation. MUST BE SET TO "0" FOR PROPER OPERATION. 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).
Bits 2-0: Bandwidth. Used to set the bandwidth of the preamp. The default is 100. When all bits are set to "1", the LM1267 will have maximum bandwidth, when all bits are set to "0" the LM1267 will have minimum bandwidth. Bit 3: Determines the polarity of the clamp signal used by the LM1267, "0" (default) is a positive clamp signal, "1" is a negative going clamp signal. Bits 7-4: Reserved Software Reset Register (I2C address 0Fh) Register name: Software Reset (0Fh) Bit 7 RSV Bit 0: RSV RSV RSV RSV RSV RSV Bit 0 SRST
Bit 1:
Bit 2: Bit 3:
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
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LM1267 150 MHz I2C RGB Video Amplifier System with OSD and DACs
Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number LM1267N NS Package Number N24C
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