TA0321 STMICROELECTRONICS | Alldatasheet

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Technical content

Lightning protection for LNB supply and control voltage regulator Introduction Communication satellites operate within two frequency bands for TV/Broadband service broadcast signals, C Band and Ku Band. The C Band overall frequency spectrum is 4.0 GHz - 8.0 GHz, while the Ku Band overall frequency spectrum is 10.7 GHz - 18.4 GHz. Within these bands each satellite has a specific uplink and downlink frequency allocation. For example: ■ C Band downlink frequency is 3.7 GHz-4.2 GHz and uplink frequency is 5.925 GHz-6.425 GHz To use the frequencies that are available for satellite broadcast as efficiently as possible, and to accommodate an additional number of channels within a given frequency band, the transmission signal can be formatted to be either vertical and horizontal, or circular right-hand and circular left-hand simultaneously per frequency. UPLINK DOWNLINK

  • Down conversion of the incoming signal from GHz range to the 910 MHz - 2150 MHz (for Europe) range called “first conversion signal”. This conversion allows the signal to be carried by an inexpensive coaxial cable towards the receiver.
  • Signal amplification with good noise figure. The LNB improves the first conversion signal level through the use of a built-in low noise amplifier.
  • Selection of Vertical or Horizontal polarization.
  • Selects operating band by switching its internal oscillator from Low band to High band when the LNB “receives” a 22kHz tone. Specifically, the local oscillator (LO) frequency changes from 9.75 GHz to 10.6 GHz. – C Band - LO frequency 9.75 GHz – Ku Band - LO frequency 10.6 GHz
  • Miscellaneous functions based on 22kHz tone PPM encoding, as discussed later in this paper.

Figure 1. OMNI-LNB architecture

2 Polarization selection

(horizontal or vertical) or Circular (right-hand or left-hand). Figure 2. The four different ways of polarization Generally, only two signals 13 V and 18 V are used with one type of antenna.

18 V(2) - Horizontal Polarization or Circular Left-Hand Polarization (LHCP)

  1. actually from 11.5 to 14V
  2. actually from 15.5 to 21V
  • Low Band (10.7-11.7 GHz)
  • High Band (11.7-12.75 GHz). This is done with the use of a 22kHz tone frequency. A 22 kHz pulse-position modulated signal of about 0.6 V amplitude is superimposed on the LNB's DC power rail. Its coding scheme also allows the remote electronics to perform more complex functions. Traditionally, when other encoding functions do not require the 22 kHz tone, simple presence or absence of this tone selects the operating band by changing the local oscillator frequency of the LNB. The complex encoding of the 22 kHz burst is done with a more sophisticated communication bus protocol named the DiSEqC standard (Digital Satellite Equipment Control). The open DiSEqC standard developed by the European Telecommunication Satellite Organization is a well accepted worldwide standard for communication between satellite receivers and satellite peripheral equipment. The 22 kHz oscillator has to be a tone generator with specific rise and fall time. The wave shape will be a quasi-square wave (sine with flat-top). The required frequency tolerance is ±2 kHz over line and temperature variations.

Table 1. Band and polarization selection table

13 V Vertical polarization Vertical polarization

18 V Horizontal polarization Horizontal polarization

3.2 Modulation method

Figure 3. Modulation scheme Figure 4. Timing diagram for tone burst control signal

4 The Need for Lightning Protection TA0321

4 The Need for Lightning Protection

to 18V DC is generated by a dedicated IC, a LNB Voltage Regulator. generate high current - high voltage surge at the voltage regulator.

  • tr/tf = 8/20 µs
  • Vpp = 3 kV to 6 kV
  • R = 12 Ω
  • Ipp = 250 A to 500 A

Figure 5. IEC61000-4-5 current waveform

5 STMicroelectronics solution

and optimized LNBTVSx-22x devices.

5.1 A segmented & differentiated approach

device relative to the various LNB voltage regulator absolute maximum ratings capabilities. optimize the cost and robustness of the total solution. See Table 3 for recommended fit.

5.2 Features

  • 3 kV, 4 kV and 6 kV protection (8/20 µs)
  • Axial & SMD package
  • Low Vf
  • Low Clamping factor
  • Fast Response Time
  • UL Recognized

Figure 6. Surge tests +4 kV (Standard IEC61000-4-5 - with series resistor of 12 Ω)

5 STMicroelectronics solution TA0321

5.3 Ordering information scheme

Table 2. LNBTVSx-22xx range

5.4 Application diagram

Table 3. Recommended fit between LNB Voltage Regulator and LNBTVSx-22xx

5.5 Benefits

  • Simple and Low Cost Solution
  • Replace current solutions at lower cost and better performances
  • High Reliability Protection Solution
  • Dedicated and Optimized for LNB Voltage Regulator protection
  • Complies with LNB supply voltages
  • Complies with IEC61000-4-5 standard
  • Available in Axial and SMD package
  • Compatible with all LNB Voltage Regulator types and references Criteria Benefits LNBTVSx-22xx Competition Lightning Protection Up to 6 kV - 500 A ++ + Reliability, longevity No diode paralleling ++ - Coverage vs LNB Reg. Various P/N ++ - Cost Low ++ + Design and safety Dedicated for LNB Reg. protection ++ +

6 Conclusion

As explained and demonstrated, all LNB power supplies have to be protected against lightning. The best in class solution for cost effective and reliable protection are the new LNVTVSx-22xx devices from STMicroelectronics. All devices are available and are in mass production.

7 Revision history

09-Jan-2006 1 Initial release.

7 Revision history TA0321

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publicati on are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectro nics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2006 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Ital y - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America