LNBS21_04

LNBS21 LNB SUPPLY AND CONTROL IC WITH STEP-UP CONVERTER AND I2C INTERFACE s s s s s s s s s s COMPLETE INTERFACE BETWEEN LNB AND I2CTM BUS BUILT-IN DC/DC CONTROLLER FOR SINGLE 12V SUPPLY OPERATION ACCURATE BUILT-IN 22KHz TONE OSCILLATOR SUITS WIDELY ACCEPTED STANDARDS FAST OSCILLATOR START-UP FACILITATES DiSEqCTM ENCODING BUILT-IN 22KHz TONE DETECTOR SUPPORTS BI-DIRECTIONAL DiSEqCTM LOOP-THROUGH FUNCTION FOR SLAVE OPERATION LNB SHORT CIRCUIT PROTECTION AND DIAGNOSTIC CABLE LENGTH DIGITAL COMPENSATION INTERNAL OVER TEMPERATURE PROTECTION PowerSO-20 DESCRIPTION Intended for analog and digital satellite STB receivers/SatTV, sets/PC cards, the LNBS21 is a monolithic voltage regulator and interface IC, Figure 1: Schematic Diagram Gate Sense Step-up Controller assembled in PowerSO-20, specifically designed to provide the power and the 13/18V, 22KHz tone signalling to the LNB downconverter in the antenna or to the multiswitch box. In this application field, it offers a complete solution with extremely low component count, low power dissipation together with simple design and I2CTM standard interfacing. This IC has a built in DC/DC step-up controller that, from a single supply source ranging from 8 to 15V, generates the voltages that let the linear LNBS21 LT1 Feedback LT2 Vup Vcc Byp OUT Preregul.+ U.V.lockout +P.ON res. Enable I Select V Select Linear Post-reg +Modulator +Protections EXTM SDA SCL ADDR DSQIN I²C interf. 22KHz Oscill. Diagnostics DETIN Tone Detector DSQOUT October 2004 Rev. 3 1/21 LNBS21 post-regulator to work at a minimum dissipated power. An UnderVoltage Lockout circuit will disable the whole circuit when the supplied VCC drops below a fixed threshold (6.7V typically). The internal 22KHz tone generator is factory trimmed in accordance to the standards, and can be controlled either by the I2CTM interface or by a dedicated pin (DSQIN) that allows immediate DiSEqCTM data encoding (*). All the functions of this IC are controlled via I2CTM bus by writing 6 bits on the System Register (SR, 8 bits). The same register can be read back, and two bits will report the diagnostic status. When the IC is put in Stand-by (EN bit LOW), the power blocks are disabled and the loop-through switch between LT1 and LT2 pins is closed, thus leaving all LNB powering and control functions to the Master Receiver (**). When the regulator blocks are active (EN bit HIGH), the output can be logic controlled to be 13 or 18 V (typ.) by mean of the VSEL bit (Voltage SELect) for remote controlling of non-DiSEqC LNBs. Additionally, it is possible to increment by 1V (typ.) the selected voltage value to compensate for the excess voltage drop along the coaxial cable (LLC bit HIGH). In order to minimize the power dissipation, the output voltage of the internal step-up converter is adjusted to allow the linear regulator to work at minimum dropout. Another bit of the SR is addressed to the remote control of non-DiSEqC LNBs: the TEN (Tone ENable) bit. When it is set to HIGH, a continuous 22KHz tone is generated regardless of the DSQIN pin logic status. The TEN bit must be set LOW when the DSQIN pin is used for DiSEqCTM encoding. The fully bi-directional DiSEqCTM interfacing is completed by the built-in 22KHz tone detector. Its input pin (DETIN) must be AC coupled to the DiSEqCTM bus, and the extracted PWK data are available on the DSQOUT pin (*). In order to improve design flexibility and to allow implementation of newcoming LNB remote control standards, an analogic modulation input pin is available (EXTM). An appropriate DC blocking capacitor must be used to couple the modulating signal source to the EXTM pin. When external modulation is not used, the relevant pin can be left open. The current limitation block has two thresholds that can be selected by the ISEL bit of the SR; the lower threshold is between 650 and 900mA (ISEL=HIGH), while the higher threshold is between 750 and 1000mA (ISEL=LOW). The current protection block is SOA type. This limits the short circuit current (ISC) typically at 300mA with ISEL=HIGH and at 400mA with ISEL=LOW when the output port is connected to ground. It is possible to set the Short Circuit Current protection either statically (simple current clamp) or dynamically by the PCL bit of the SR; when the PCL (Pulsed Current Limiting) bit is set to LOW, the overcurrent protection circuit works dynamically: as soon as an overload is detected, the output is shut-down for a time toff, typically 900ms. Simultaneously the OLF bit of the System Register is set to HIGH. After this time has elapsed, the output is resumed for a time ton=1/ 10toff (typ.). At the end of ton, if the overload is still detected, the protection circuit will cycle again through Toff and Ton. At the end of a full Ton in which no overload is detected, normal operation is resumed and the OLF bit is reset to LOW. Typical Ton+Toff time is 990ms and it is determined by an internal timer. This dynamic operation can greatly reduce the power dissipation in short circuit condition, still ensuring excellent power-on start up in most conditions (**). However, there could be some cases in which an highly capacitive load on the output may cause a difficult start-up when the dynamic protection is chosen. This can be solved by initiating any power start-up in static mode (PCL=HIGH) and then switching to the dynamic mode (PCL=LOW) after a chosen amount of time. When in static mode, the OLF bit goes HIGH when the current clamp limit is reached and returns LOW when the overload condition is cleared. This IC is also protected against overheating: when the junction temperature exceeds 150°C (typ.), the step-up converter and the linear regulator are shut off, the loop-trough switch is opened, and the OTF bit of the SR is set to HIGH. Normal operation is resumed and the OTF bit is reset to LOW when the junction is cooled down to 140°C (typ.). (*): External components are needed to comply to bi-directional DiSEqCTM bus hardware requirements. Full compliance of the whole application to DiSEqCTM specifications is not implied by the use of this IC. (**): The current limitation circuit has no effect on the loop-through switch. When EN bit is LOW, the current flowing from LT1 to LT2 must be externally limited. 2/21 LNBS21 Table 1: Ordering Codes TYPE LNBS21 PowerSO-20 (Tube) LNBS21PD PowerSO-20 (Tape & Reel) LNBS21PD-TR Table 2: Absolute Maximum Ratings Symbol VCC VUP IO VO VI VDETIN VOH ILT VLT IGATE VSENSE Tstg Top DC Input Voltage DC Input Voltage Output Current DC Output Pin Voltage Logic Input Voltage (SDA, SCL, DSQIN) Detector Input Signal Amplitude Logic High Output Voltage (DSQOUT) Bypass Switch ON Current Bypass Switch OFF Voltage Gate Current Current Sense Voltage Storage Temperature Range Operating Junction Temperature Range Parameter Value 16 25 20 Internally Limited -0.3 to 22 -0.3 to 7 2 7 900 ±20 ±400 -0.3 to 1 -0.3 to 7 -40 to +150 -40 to +125 Unit V V V mA V V VPP V mA V mA V V °C °C VLT1, VLT2 DC Input Voltage VADDRESS Address Pin Voltage Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied. Table 3: Thermal Data Symbol Rthj-case Parameter Thermal Resistance Junction-case PowerSO-20 2 Unit °C/W Figure 2: Pin Connection (top view) PowerSO-20 3/21 LNBS21 Table 4: Pin Description SYMBOL VCC NAME Supply Input FUNCTION 8V to 15V supply. A 220µF bypass capacitor to GND with a 470nF (ceramic) in parallel is recommended External MOS switch Gate connection of the step-up converter Current Sense comparator input. Connected to current sensing resistor Input of the linear post-regulator. The voltage on this pin is monitored by internal step-ut controller to keep a minimum dropout across the linear pass transistor Output of the linear post regulator modulator to the LNB. See truth table for voltage selections. Bidirectional data from/to I2C bus. Clock from I2C bus. When the TEN bit of the System Register is LOW, this pin will accept the DiSEqC code from the main µcontroller. The LNBS21 will use this code to modulate the internally generated 22kHz carrier. Set to GND the pin if not used. 22kHz Tone Detector Input. Must be AC coupled to the DiSEqC bus. Open collector output of the tone Detector to the main µcontroller for DiSEqC data decoding. It is LOW when tone is detected. External Modulation Input. Need DC decoupling to the AC source. If not used, can be left open. Pins to be connected to ground. Needed for internal preregulator filtering In standby mode the power switch between LT1 and LT2 is closed. Max allowed current is 900mA. this pin can be left open if loop through function is not needed. Same as above bus addresses available by setting the Four Address Pin level voltage I2C PIN NUMBER vs. PACKAGE 18 GATE SENSE Vup External Switch Gate Current Sense Input Step-up Voltage 17 16 19 OUT SDA SCL DSQIN Output Port Serial Data Serial Clock DiSEqC Input 2 12 13 14 DETIN Detector In 9 15 DSQOUT DiSEqC Output EXTM GND BYP LT1 External Modulator Ground Bypass Capacitor Loop Through Switch 5 1, 6, 10, 11, 20 8 4 LT2 ADDR Loop Through Switch Address Setting 3 7 4/21 LNBS21 Figure 3: Typical Application Circuit D1 1N4001 IC1 Master STB Vup C2 220µF C3 470nF Ceramic LT1 C7 10nF IC2 (Note 3) STS4DNFS30L LT2 270µH Gate Vo C8 10nF D2 BAT43 to LNB LNBS21 L1=22µH Rsc 0.1Ω 15 ohm see Note 2 DETIN (Note 1) Byp Sense (Note 4) C6 10nF Vcc C5 470nF Vin 12V C1 220µF C4 470nF Ceramic DSQIN(Note 1) SCL SDA GND EXTM ADDRESS DSQOUT 0