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PDF LM1237 Data sheet ( Hoja de datos )
| Número de pieza | LM1237 | |
| Descripción | 150 MHz I2C Compatible RGB Preamplifier with Internal 254 Character OSD and 4 DACs | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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September 2002
LM1237
150 MHz I2C Compatible RGB Preamplifier with Internal
254 Character OSD and 4 DACs
General Description
The LM1237 pre-amp is an integrated CMOS CRT preamp.
It has an I2C compatible interface which 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 which are well
matched to the LM2479 and LM2480 integrated bias clamp
ICs. The LM1237 preamp is also designed to be compatible
with the LM246x high gain driver family.
Black level clamping of the video signal is carried out directly
on the AC coupled input signal into the high impedance
preamplifier input, thus eliminating the need for additional
clamp capacitors. Horizontal and vertical blanking of the
outputs is provided. Vertical blanking is optional and its
duration is register programmable.
The IC is packaged in an industry standard 24 lead DIP
molded plastic package.
Features
n I2C compatible microcontroller interface
n Internal 254 character OSD usable as either (a) 190
2-color plus 64 4-color characters, (b) 318 2-color
characters, or (c) some combination in between.
n OSD override allows OSD messages to override video
and the use of burn-in screens with no video input
n 4 DAC outputs (8-bit resolution) for bus controlled CRT
bias and brightness
n Spot killer which blanks the video outputs when VCC
falls below the specified threshold
n Suitable for use with discrete or integrated clamp, with
software configurable brightness mixer
n H and V blanking (V blanking is optional and has
register programmable width)
n Power Saving Mode with 80% power reduction
n Matched to LM246x driver and LM2479/80 drivers
Applications
n Low end 15" and 17" bus controlled monitors with OSD
n 1024x768 displays up to 85 Hz requiring OSD capability
n Very low cost systems with LM246x driver
Block and Connection Diagram
FIGURE 1. Order Number LM1237AAF/NA
See NS Package Number N24D
© 2002 National Semiconductor Corporation DS200234
20023401
www.national.com
1 page  
System Interface Signal Characteristics (Continued)
Unless otherwise noted: TA = 25˚C, VCC = +5.0V, VIN = 0.7V, VABL = VCC, CL = 8 pF, Video Outputs = 2.0 VP-P. See Note 7
for Min and Max parameters and Note 6 for Typicals. DAC parameters apply to all 4 DACs.
Symbol
Parameter
Conditions
Min Typ Max Units
tCLAMP-VIDEO
Time from End of Clamp Pulse to Referenced to Blue, Red and Green
Start of Video
inputs
50
ns
Note 1: Limits of Absolute Maximum Ratings indicate 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: Input from signal generator: tr, tf < 1 ns.
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 and 5V Dig 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 maximum variation in step height of a 16 step staircase input signal waveform with a 0.7 VP-P level at the input. All 16 steps equal,
with each at least 100 ns in duration.
Note 10: dt/dVCC = 200*(t5.5V–t4.5V)/ ((t5.5V + t4.5V)) %/V, where:
t5.5V is the rise or fall time at VCC = 5.5V, and t4.5V is the rise or fall time at VCC = 4.5V.
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 AVC−50% 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 AVC−50%. 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 −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: Machine Model ESD test is covered by specification EIAJ IC-121-1981. A 200 pF cap is charged to the specific voltage, then discharged directly into the
IC with no external series resistor (resistance of discharge path must be under 50Ω).
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 the guaranteed minimum 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: Adjust input frequency from 10 MHz (AV max reference level) to the −3 dB corner frequency (f−3 dB).
Note 17: Once the spot killer has been activated, the LM1237 remains in the off state until VCC is cycled (reduced below 0.5V andthen restored to 5V).
Hexadecimal and Binary Notation
Hexadecimal numbers appear frequently throughout this document, representing slave and register addresses, and register
values. These appear in the format “0x...”. For example, the slave address for writing the registers of the LM1237 is hexadecimal
BA, written as 0xBA. On the other hand, binary values, where the individual bit values are shown, are indicated by a trailing “b”.
For example, 0xBA is equal to 10111010b. A subset of bits within a register is referred to by the bit numbers in brackets following
the register value. For example, the OSD contrast bits are the fourth and fifth bits of register 0x8438. Since the first bit is bit 0,
the OSD contrast register is 0x8438[4:3].
Register Test Settings
Table 1 shows the definitions of the Test Settings 1–8 referred to in the specifications sections. Each test setting is a combination
of five hexadecimal register values, Contrast, Gain (Blue, Red, Green) and DC offset.
Control No. of Bits
Contrast
7
B, R, G
Gain
DC Offset
7
3
1
0x7F
(Max)
0x7F
(Max)
0x00
(Min)
TABLE 1. Test Setting Definitions
2
0x00
Min
0x7F
(Max)
0x05
3
0x7F
(Max)
0x7F
(Max)
0x07
(Max)
Test Settings
45
0x7F
0x40
(Max)
(50.4%)
Set VO to
2 VP-P
0x05
0x7F
(Max)
0x05
6
0x7F
(Max)
0x40
(50%)
0x05
7
0x7F
(Max)
0x00
(Min)
0x05
8
0x7F
(Max)
0x7F
(Max)
0x05
5 www.national.com
5 Page 
Pin Descriptions and Application Information (Continued)
Pin
Pin Name
No.
22 ABL
23 CLAMP
Schematic
Description
The Automatic Beam Limiter input is biased to
the desired beam current limit by RABL and VBB
and normally keeps DINT forward biased. When
the current resupplying the CRT capacitance
(averaged by CABL) exceeds this limit, then DINT
begins to turn off and the voltage at pin 22
begins to drop. The LM1237 then lowers the
gain of the three video channels until the beam
current reaches an equilibrium value.
This pin accepts either TTL or CMOS logic
levels. The internal switching threshold is
approximately one-half of VCC. An external
series resistor, R31, of about 1k is recommended
to avoid overdriving the input devices. In any
event, REXT must be large enough to prevent the
voltage at pin 23 from going higher than VCC or
below GND.
24 H Flyback
Proper operation requires current reversal. RH
should be large enough to limit the peak current
at pin 24 to about +4 ma during blanking, and
−500 µA during scan. C17 is usually needed for
logic level inputs and should be large enough to
make the time constant, RHC17 significantly
larger than the horizontal period. R34 and C8 are
typically 300 ohms and 330 pf when the flyback
waveform has ringing and needs filtering. C18
may be needed to filter extraneous noise and
can be up to 100 pF.
11 www.national.com
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LM1237.PDF ] | |
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