データシートサーチシステム |
|
LM1270N データシート(PDF) 9 Page - National Semiconductor (TI) |
|
|
LM1270N データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 27 page Functional Description (Continued) Using the data encoded on the video eliminates one stage of communicating with the LM1270, allowing for a faster re- sponse time for changes in the Hi-Brite window. V REF Proper operation of the LM1270 does require a very accu- rate reference voltage. This voltage is generated in the V REF block. To insure an accurate voltage over temperature, an external resistor is used to set the current in the V REF stage. The external resistor is connected to pin 23. This resistor should be 1% and have a temperature coefficient under 100 ppm/˚C. ALL VIDEO SIGNALS MUST BE KEPT AWAY FROM PIN 23. 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 12 is a good example of trace routing near pin 23. The output of the V REF stage goes to a number of blocks in the video section and also to pin 22. 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 µA. Pin 22 is bi-directional, allowing the LM1270 to be referenced to a pre-amp V REF. This configuration makes it possible to DC couple to the pre-amp, but for accurate DC level, it is recommended that AC coupling be used between the LM1270 and the pre-amp. It is also recommended that the internal V REF be used for best performance. Note: Any noise injected into pin 22 will appear on the video. The voltage reference must be kept very clean for best perfor- mance of the LM1270. H FLYBACK H Flyback is an analog signal input from the monitor hori- zontal scan. This flyback signal goes to the internal horizon- tal flyback pulse generation circuit. An optional capacitor and/or resistor to ground may be needed if noise interferes with the H Flyback signal or if there is ringing on the H Flyback signal. Note: there is no blanking pedestal on the output video. If horizontal blanking is to be added to the video signal it must be done at the pre-amp. R LIMIT is used to limit the input current into the IC to a maximum 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, R LIMIT = 100 k Ω. The internal input imped- ance of pin 16 is low to limit the maximum voltage swing at the input to be within the supply rail and ground. Figure 2 shows the H flyback waveforms and the location of R LIMIT.A 56 pF capacitor has been added to the H Flyback pin for filtering noise on the H Flyback signal. VERTICAL BLANKING A similar vertical pulse generation circuit to the LM1238 is included internal to the LM1270. The leading edge of the vertical sync is used to start the programmable vertical blanking signal directly. The Vertical Blank Duration Control Register sets the width of the pulse. When vertical blanking is enabled its polarity is programmable. CLAMPING Pin 24, the clamp pin, can be set for either an input or and output. If used as an input, then this pin functions just like the clamp input pins to the video pre-amps. One should use a series 1 k Ω resistor to pin 24 and a small capacitor may also be needed between pin 24 and ground to filter high fre- quency noise. 20063519 FIGURE 2. H Flyback Input Pulse www.national.com 9 |
同様の部品番号 - LM1270N |
|
同様の説明 - LM1270N |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |