LM1237BDBC/NA National Semiconductor, LM1237BDBC/NA Datasheet - Page 8

• Manufacturer Part Number: LM1237BDBC/NA
• Description: Video ICs, 150MHz I2C Compatible RGB Preamplifier with Internal 254 Character OSD and 4 DACs
• Manufacturer: National Semiconductor

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Typical Performance Characteristics
ABL Gain Reduction
The ABL function reduces the contrast level of the LM1237 as the voltage on pin 22 is lowered from V
8 shows the amount of gain reduction as the voltage is lowered from V
reaches the knee anound 3.7V, where the slope increases. Many system designs will require about 3 to 5 dB of gain reduction
in full beam limiting. Additional attenuation is possible, and can be used in special circumstances. However, in this case, video
performance such as video linearity and tracking between channels will tend to depart from normal specifications.
OSD Phase Locked Loop
Table 3. OSD Register recommendations shows the recommended horizontal scan rate ranges (in kHz) for each combination of
PLL register setting, 0x843E [1:0], and the pixels per line register setting, 0x8401 [7:5]. These ranges are recommended for chip
ambient temperatures of 50
these ranges, the performance of the loop will be improved if these recommendations are followed. NR means the combination
of PLL and PPL is not recommended for any scan rate.
PLL=1
PLL=2
PLL=3
27 - 57
PPL=0
NR
NR
o
C to 70
26 - 49
PPL=1
NR
NR
o
C. While the OSD PLL will lock for other register combinations and at scan rates outside
TABLE 3. OSD Register recommendations
FIGURE 8. ABL Gain Reduction Curve
25 - 45
45 - 89
PPL=2
NR
82 - 110
25 - 41
41 - 82
PPL=3
V
8
CC
= 5V, T
75 - 110
25 - 37
37 - 75
PPL=4
CC
A
(5.0V) to 2V. The gain reduction is small until V
= 25˚C unless otherwise specified (Continued)
69 - 110
25 - 34
34 - 69
PPL=5
CC
64 - 110
20023460
25 - 32
32 - 64
PPL=6
to around 2 volts. Figure
60 - 110
25 - 30
30 - 60
PPL=7
22