Part # Application Note General Purpose Products LNBP21 AN1550 datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: LNBP21: a DiSEqCdatasheet 2.0 compliant single supply solution for LNB power and logic control


Part Details:

AN1550 APPLICATION NOTE LNBP21: A DiSEqCTM 2.0 COMPLIANT SINGLE SUPPLY SOLUTION FOR LNB POWER AND LOGIC CONTROL S. Mauro 1. INTRODUCTION. A typical satellite receiver system is formed by the blocks reported in figure 1:- The parabola is the antenna of the system and focuses the satellite signal to the LNB;- The LNB (low noise block) is placed on the focus of the parabola and converts the incoming signal inthe 10GHz range to a lower frequency signal (in the 1-2GHz range) called "first conversion signal". Figure 1: Basic Satellite TV Installation LNB Parabola Coaxial Cable Satellite To TV Set Receiver This allows the signal to be carried by an inexpensive coaxial cable towards the receiver. Additionally itimproves the first conversion signal level by a built-in low noise amplifier. A universal LNB can changepolarization type (Horizontal or Vertical) or operative band by command signals sent by the receiver. - The coaxial cable joins the LNB to the receiver and carries out 3 functions:a) to transfer the first conversion signal from the LNB to the receiver;b) to transfer command signals from the receiver to the LNB to change polarization or signal band;c) to carry the DC voltage to supply the LNB. - The receiver converts the first conversion signal in control signals for the TV system. The supply/interface block is placed inside the receiver, which provides for two important features:- to supply the LNB block- to generate all the signals/voltages that LNB needs to operate correctly. The supply/interface block must perform the following functions:- be ready to accept future digital standards with an external modulation input and fast oscillator start-up;- implement the loop-through function in slave condition for single dish, multiple receiver system; July 2002 1/19 AN1550 - APPLICATION NOTE - accept the paralleling of 2 or more receivers and in this condition avoid the flow of reverse current fromthe output to GND;- give accurate, thermal compensated outputs with the possibility to compensate the DC voltage dropcaused by long coaxial cables;- be reliable;- provide overload (better if a dynamic one) and thermal protection with diagnostic;- avoid every type of trimming;- provide the possibility to be driven by a microcontroller or a simple digital logic to implement all thesefunctions;- it must be cheap and get a small area on the board. All these functions are hard to be implemented with discrete components, but are greatly made easier byusing an integrated device as like LNBP21 that has been specially designed for the purpose. 1.2. LNBP21. LNBP21 is the integrated solution for supplying/interfacing satellite LNB modules. It gives goodperformance in a simple and economical way, with minimum use of external components. It comprises alot of functions that allow to realize LNB supplying/interfacing in accordance to the international standards. Besides, it includes an I2CTM(*) bus interface and, thanks to an integrated step-up DC/DCcontroller, it works with a single input voltage supply. 2. BLOCK DIAGRAM GENERAL DESCRIPTION. Here below a description of the LNBP21 internal blocks. 2.1. Step-up Controller. The LNBP21 has a built in step-up DC/DC converter controller that, from a single supply source rangingfrom 8V to 15V, generates the voltages that let the linear post-regulator work at a minimum powerdissipation. The DC/DC converter external components will be connected to the Gate, Sense and VUPpins. 2.2. Preregulator + U. V. Lockout + P. On Reset. This block includes a 5V voltage reference connected to the Byp pin, an Undervoltage Lockout circuit,intended to disable the whole circuit when the supplied Vcc drops below a fixed threshold (6.7V typ.), and a Power On Reset that sets all the I2C registers to zero when the Vcc is turned on and rises fromzero above the on threshold (7.3V typ). 2.3. I2C Interface. All the functions of this IC, except for the DETIN/ DSQOUT, are controlled via I2C bus by writing 6 bits onthe System Register (SR, 8 bits). The same register can be read back, and two bits will report the diagnostic status. The LNBP21 I2C interface Address can be selected among four different addressesby setting the voltage level of the dedicated ADDR pin. 2/19 AN1550 - APPLICATION NOTE 2.4. 22kHz Oscillator. The internal 22kHz tone generator is factory trimmed in accordance to the standards, and can be controlled either by the I2C interface or by a dedicated pin (see DSQIN in figure 2) that allows immediateDiSEqCTM(**) data encoding. The rise and fall edges are controlled to be in the 5µs to 15µs range, 8µstyp., to avoid RF pollution towards the receiver. The Duty cycle is 50% typ. It modulates the DC outputwith a ± 0.35V amplitude and 0V average. Figure 2: Block Diagram Gate LT1 Sense Step-up Feedback Controller LT2 VUP OUT


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Application Note General Purpose Products LNBP21 AN1550.pdf Datasheet