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| 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, 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 IC interf. 22KHz Oscill. Diagnostics DETIN Tone Detector DSQOUT November 2002 1/19 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 minimise 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 encoding. The fully bi-directional DiSEqCTM 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 capaci-tor 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 dy-namically 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 150C (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 140C (typ.). (*): External components are needed to comply to bi-directional DiSEqCTM bus hardware require-ments. 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. 2/19 LNBS21 ORDERING CODES TYPE LNBS21 PowerSO-20 (Tube) LNBS21PD PowerSO-20 (Tape & Reel) LNBS21PD-TR 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. THERMAL DATA Symbol Rthj-case Parameter Thermal Resistance Junction-case PowerSO-20 2 Unit C/W PIN CONFIGUARATION (top view) PowerSO-20 3/19 LNBS21 TABLE A: PIN CONFIGURATIONS SYMBOL VCC NAME Supply Input FUNCTION 8V to 15V supply. A 220F 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 bus. When the TEN bit of the System Register is LOW, this pin will accept the DiSEqC code from the main controller. The LNBS21 will use this code to modulate the internally generated 22kHz carrier. Set to GND thi pin if not used. 22kHz Tone Detector Input. Must be AC coupled to the DiSEcQ bus. Open collector output of the tone Detector to the main controller for DiSEcQ 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. Circuit Ground. It is internally connected to the die frame for heat dissipation. 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 loopthrough function is not needed. Same as above Four I C bus addresses available by setting the Address Pin level voltage 2 PIN NUMBER vs PACKAGE 18 GATE SENSE Vup Exrernal 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 I2C DETIN Detector In 9 15 DSQOUT DiSEqC Output EXTM GND BYP LT1 Extrernal Modulator Ground Bypass Capacitor Loop Through Switch 5 1, 10, 11, 20 8 4 LT2 ADDR Loop Through Switch Address Setting 3 7 4/19 LNBS21 TYPICAL APPLICATION CIRCUIT D1 1N4001 IC1 Master STB Vup C2 220F C3 470nF Ceramic LT1 C7 10nF Schottky diode STPS3L40S or 1N5821 LT2 270H Gate MOSFET STN4NF03L to LNB Vout C8 10nF D2 BAT43 LNBS21 Sense DETIN(*) 15 ohm (**) see note L1=22H Rsc 0.05 C6 10nF Byp Vcc C5 470nF Vin 12V C1 220F C4 470nF Ceramic DSQIN(*) SCL SDA GND EXTM ADDRESS DSQOUT 0 I2C BUS INTERFACE Data transmission from main P to the LNBS21 and viceversa takes place through the 2 wires I2C bus interface, consisting of the two lines SDA and SCL (pull-up resistors to positive supply voltage must be externally connected). DATA VALIDITY As shown in fig. 1, the data on the SDA line must be stable during the high period of the clock. The HIGH and LOW state of the data line can only change when the clock signal on the SCL line is LOW. START AND STOP CONDITIONS As shown in fig.2 a start condition is a HIGH to LOW transition of the SDA line while SCL is HIGH. The stop condition is a LOW to HIGH transition of the SDA line while SCL is HIGH. A STOP condi-tions must be sent before each START condition. BYTE FORMAT Every byte transferred to the SDA line must contain 8 bits. Each byte must be followed by an ac-knowledge bit. The MSB is transferred first. ACKNOWLEDGE The master (P) puts a resistive HIGH level on the SDA line during the acknowledge clock pulse (see fig. 3). The peripheral (LNBS21) that acknowledges has to pull-down (LOW) the SDA line during the acknowledge clock pulse, so that the SDA line is stable LOW during this clock pulse. The peripheral which has been addressed has to generate an acknowledge after the reception of each byte, other-wise the SDA line remains at the HIGH level during the ninth clock pulse time. In this case the master transmitter can generate the STOP information in order to abort the transfer. The LNBS21 won't gen-erate the acknowledge if the Vcc supply is below the Undervoltage Lockout threshold (6.7V typ.). TRANSMISSION WITHOUT ACKNOWLEDGE Avoiding to detect the acknowledge of the LNBS21, the P can use a simpler transmission: simply it waits one clock without checking the slave acknowledging, and sends the new data. This approach of course is less protected from misworking and decreases the noise immunity. 5/19 LNBS21 Figure 1 : DATA VALIDITY ON THE I2C BUS Figure 2 : TIMING DIAGRAM ON I2C BUS Figure 3 : ACKNOWLEDGE ON I2C BUS 6/19 LNBS21 LNBS1 SOFTWARE DESCRIPTION INTERFACE PROTOCOL The interface protocol comprises: - A start condition (S) CHIP ADDRESS MSB 0 LSB MSB R/W ACK - A chip address byte = hex 10 / 11 (the LSB bit determines read(=1)/write(=0) transmission) - A sequence of data (1 byte + acknowledge) - A stop condition (P) DATA LSB ACK P S 0 0 1 0 0 0 ACK= Acknowledge S= Start P= Stop R/W= Read/Write SYSTEM REGISTER (SR, 1 BYTE) MSB R, W PCL R, W ISEL R, W TEN R, W LLC R, W VSEL R, W EN R OTF LSB R OLF R,W= read and write bit R= Read-only bit All bits reset to 0 at Power-On TRANSMITTED DATA (I2C BUS WRITE MODE) When the R/W bit in the chip address is set to 0, the main P can write on the System Register (SR) of the LNBS21 via I2C bus. Only 6 bits out of PCL ISEL TEN LLC VSEL 0 0 1 1 0 1 0 1 0 1 X 0 1 0 1 EN 1 1 1 1 1 1 1 1 1 1 0 OTF X X X X X X X X X X X OLF X X X X X X X X X X X the 8 available can be written by the P, since the re-maining 2 are left to the diagnostic flags, and are read-only. Function VOUT=13V, VUP=16V Loopthrough switch open VOUT=18V, VUP=21V Loopthrough switch open VOUT=14V, VUP=17V Loopthrough switch open VOUT=19V, VUP=22V Loopthrough switch open 22KHz tone is controlled by DSQIN pin 22KHz tone is ON, DSQIN pin disabled IOUT(min)=750mA, IOUT(max)=1A ISC=300mA IOUT(min)=600mA, IOUT(max)=900mA ISC=300mA Pulsed (dynamic) current limiting is selected Static current limiting is selected Power blocks disabled, Loopthrough switch closed X X X X X= don't care. Values are typical unless otherwise specified RECEIVED DATA (I2C bus READ MODE) The LNBS21 can provide to the Master a copy of the SYSTEM REGISTER information via I2C bus in read mode. The read mode is Master activated by sending the chip address with R/W bit set to 1. At the following master generated clocks bits, the LNBS21 issues a byte on the SDA data bus line (MSB transmitted first). At the ninth clock bit the MCU master can: - acknowledge the reception, starting in this way the transmission of another byte from the LNBS21; 7/19 LNBS21 - no acknowledge, stopping the read mode communication. PCL ISEL TEN LLC VSEL EN OTF 0 These bits are read exactly the same as they were left after last write operation Values are typical unless otherwise specified While the whole register is read back by the P, only the two read-only bits OLF and OTF convey di-agnostic informations about the LNBS21. Function TJ<140C, normal operation TJ>150C, power block disabled, Loothrough switch open OLF 1 0 1 IOUT POWER-ON I2C INTERFACE RESET The I2C interface built in the LNBS21 is automatically reset at power-on. As long as the Vcc stays be-low the UnderVoltage Lockout threshold (6.7V typ.), the interface will not respond to any I2C com-mand and the System Register (SR) is initialised to all zeroes, thus keeping the power blocks disabled. Once the Vcc rises above 7.3V, the I2C interface becomes operative and the SR can be configured by the main P. This is due to About 500mV of hysteresis provided in the UVL threshold to avoid false retriggering of the Power-On reset circuit. DiSEqCTM IMPLEMENTATION The LNBS21 helps the system designer to implement the bi-directional (2.x) DiSEqC protocol by al-lowing an easy PWK modulation/ demodulation of the 22KHz carrier. The PWK data are exchanged between the LNBS21 and the main P using logic levels that are compatible with both 3.3 and 5V mi-crocontrollers. This data exchange is made through two dedicated pins, DSQIN and DSQOUT, in or-der to maintain the timing relationships between the PWK data and the PWK modulation as accurate as possible. These two pins should be directly connected to two I/O pins of the P, thus leaving to the resident firmware the task of encoding and decoding the PWK data in accordance to the DiSEqC pro-tocol. Full compliance of the system to the specification is thus not implied by the bare use of the LNBS21. The system designer should also take in consideration the bus hardware requirements, that include the source impedance of the Master Transmitter measured at 22KHz. To limit the attenuation at car-rier frequency, this impedance has to be 15ohm at 22KHz, dropping to zero ohm at DC to allow the power flow towards the peripherals. This can be simply accomplished by the LR termination put on the OUT pin of the LNBS, as shown in the Typical Application Circuit on page 5. Unidirectional (1.x) DiSEqC and non-DiSEqC systems normally don't need this termination, and the OUT pin can be directly connected to the LNB supply port of the Tuner. There is also no need of Tone Decoding, thus, it is recommended to connect the DETIN and DSQOUT pins to ground to avoid EMI. ADDRESS PIN Connecting this pin to GND the Chip I2C interface address is 0001000, but, it is possible to choice among 4 different addresses simply setting this pin at 4 fixed voltage levels (see table on page 10). ELECTRICAL CHARACTERISTICS FOR LNBS SERIES (TJ = 0 to 85C, EN=1, LLC=0, TEN=0, ISEL=0, PCL=0, DSQIN=0, VIN=12V, IOUT=50mA, unless otherwise specified. See software description section for I2C access to the system register) Symbol VIN VLT1 IIN VO VO Parameter Supply Voltage LT1 Input Voltage Supply Current Output Voltage Output Voltage IO = 0mA TEN=VSEL=LLC=1 IO = 750 mA VSEL=1 IO = 750 mA VSEL=0 EN=1 EN=0 LLC=0 LLC=1 LLC=0 LLC=1 20 2.5 18 19 13 14 Test Conditions IO = 750 mA TEN=VSEL=LLC=1 Min. 8 Typ. Max. 15 20 40 5 18.7 13.5 Unit V V mA mA V V V V 17.3 12.5 8/19 LNBS21 Symbol VO VO IMAX ISC tOFF tON fTONE ATONE DTONE tr, tf VEXTM ZEXTM VLT fSW fDETIN VDETIN ZDETIN VOL IOZ VIL VIH IIH IOBK TSHDN Parameter Line Regulation Load Regulation Output Current Limiting Output Short Circuit Current Dynamic Overload protection OFF Time Dynamic Overload protection ON Time Tone Frequency Tone Amplitude Tone Duty Cycle Tone Rise and Fall Time External Modulation Input Voltage External Modulation Impedance Loopthrough Switch Voltage Drop (lt1 to LT2) DC/DC Converter Switch Frequency Tone Detector Frequency Capture Range Tone Detector Input Amplitude Tone Detector Input Impedance Overload Flag Pin Logic LOW Overload Flag Pin OFF State Leakage Current DSQIN Input Pin Logic LOW DSQIN Input Pin Logic HIGH DSQIN Pins Input Current Output Backward Current PCL=0 PCL=0 TEN=1 TEN=1 TEN=1 TEN=1 Test Conditions VSEL=0 VSEL=1 VSEL=0 or 1 IOUT = 50 to 750mA ISEL=1 ISEL=0 ISEL=1 ISEL=0 Output Shorted Output Shorted VIN1=8 to 15V Min. Typ. 5 5 Max. 40 60 200 900 1000 Unit mV mV mV mA mA mA mA ms ms 650 750 300 400 900 tOFF/10 20 0.55 40 5 22 0.72 50 8 6 24 0.9 60 15 400 KHz Vpp % s mVpp GEXTM External Modulation Gain VOUT/VEXTM, AC Coupling f = 10Hz to 50KHz EN=0, f = 10Hz to 40KHz 260 VMI=12 or 19V 0.35 220 0.6 ILT=300mA, V kHz 0.4Vpp sinewave fIN=22kHz sinewave 18 0.2 150 24 1.5 kHz Vpp k Tone present Tone absent IOL=2mA VOH = 6V 0.3 0.5 10 0.8 V A V V 2 VIH = 5V EN=0 VOBK = 18V 15 -4 150 15 -10 A mA C C Temperature Shutdown Threshold TSHDN Temperature Shutdown Hysteresis 9/19 LNBS21 GATE AND SENSE ELECTRICAL CHARACTERISTICS (TJ = 0 to 85C, VIN=12V) Symbol Parameter Test Conditions IGATE=-100mA IGATE=100mA Min. Typ. 4.5 4.5 200 Max. Unit mV RDSON-L Gate LOW RDSON RDSON-H Gate LOW RDSON VSENSE Current Limit Sense Voltage I2C ELECTRICAL CHARACTERISTICS (TJ = 0 to 85C, VIN=12V) Symbol VIL VIH IIH VIL fMAX Parameter LOW Level Input Voltage HIGH Level Input Voltage Input Current SDA, SCL SDA, SCL SDA, SCL, VIN= 0.4 to 4.5V 2 -10 10 0.6 500 Test Conditions Min. Typ. Max. 0.8 Unit V V A V KHz DSQIN Input Pin Logic SDA (open drain), IOL = 6mA LOW Maximum Clock Frequency SCL ADDRESS PIN CHARACTERISTICS (TJ = 0 to 85C, VIN=12V) Symbol Parameter Test Conditions Min. 0 1.3 2.3 3.3 Typ. Max. 0.7 1.7 2.7 5 Unit V V V V VADDR-1 "0001000" Addr Pin Voltage VADDR-2 "0001001" Addr Pin Voltage VADDR-3 "0001010" Addr Pin Voltage VADDR-4 "0001011" Addr Pin Voltage TEST CIRCUIT 1N4001 ILT Vup STPS3L40A 220F 470nF VMI, VOBK LT1 10nF A V VLT Scope Probe STN4NF03L Gate L1=22H LT2 IOUT, IOBK 10nF Sense Rsc 0.05 Vin IIN OUT Vcc A VOUT 20F Load A 220F 470nF LNBS21 V From I2C Master { EXTM SDA SCL SDA SCL 10nF VEXTM, VDETIN DETIN DSQIN 470nF Pulse Gen. BYP ADDRESS DSQOUT VOL A V IOZ / IOL VOH / IOL 10/19 LNBS21 TYPICAL CHARACTERISTICS (unless otherwise specified Tj = 25C) Figure 4 : Output Voltage vs Temperature Figure 7 : Line Regulation vs Temperature Figure 5 : Output Voltage vs Temperature Figure 8 : Load Regulation vs Temperature Figure 6 : Line Regulation vs Temperature Figure 9 : Load Regulation vs Temperature 11/19 LNBS21 Figure 10 : Supply Current vs Temperature Figure 13 : Dynamic Overload Protection OFF Time vs Temperature Figure 11 : Supply Current vs Temperature Figure 14 : Output Current Limiting vs Temperature Figure 12 : Dynamic Overload Protection ON Time vs Temperature Figure 15 : Output Current Limiting vs Temperature 12/19 LNBS21 Figure 16 : Tone Frequency vs Temperature Figure 19 : Tone Rise Time vs Temperature Figure 17 : Tone Amplitude vs Temperature Figure 20 : Tone Fall Time vs Temperature Figure 18 : Tone Duty Cicle vs Temperature Figure 21 : Loopthrought Switch Drop Voltage vs Temperature 13/19 LNBS21 Figure 22 : Loopthrought Switch Drop Voltage vs Temperature Figure 25 : DSQOUT Pin Logic Low vs Temperature Figure 23 : Loopthrought Switch Drop Voltage vs Loopthrought Current Figure 26 : Undervoltage Lockout Threshold vs Temperature Figure 24 : Loopthrought Switch Drop Voltage vs Loopthrought Current Figure 27 : Output Backward Current vs Temperature 14/19 LNBS21 Figure 28 : DC/DC Converter Efficiency vs Temperature Figure 31 : DSQIN Tone Enable Transient Response VCC=12V, IO=50mA, EN=1, TEN=0 Figure 29 : Current Limit Sense vs Temperature Figure 32 : DSQIN Tone Enable Transient Response VCC=12V, IO=50mA, EN=1, TEN=0 Figure 30 : 22kHz Tone Figure 33 : DSQIN Tone Disable Transient Response VCC=12V, IO=50mA, EN=TEN=1 VCC=12V, IO=50mA, EN=1, TEN=0 15/19 LNBS21 Figure 34 : Output Voltage Transient Response from 13V to 18V Figure 35 : Output Voltage Transient Response from 13V to 18V VCC=12V, IO=50mA, VSEL=from 0 to 1, EN=1 VCC=12V, IO=50mA, VSEL=from 1 to 0, EN=1 TERMAL DESIGN NOTES During normal operation, this device dissipates some power. At maximum rated output current (500mA), the voltage drop on the linear regulator lead to a total dissipated power that is of about 1.7W. The heat generated requires a suitable heatsink to keep the junction temperature below the overtemperature protection threshold. Assuming a 40C temperature inside the Set-Top-Box case, the total Rthj-amb has to be less than 50C/W. While this can be easily achieved using a through-hole power package that can be attached to a small heatsink or to the metallic frame of the receiver, a surface mount power package must rely on PCB solutions whose thermal efficiency is often limited. The simplest solution is to use a large, con-tinuous copper area of the GND layer to dissipate the heat coming from the IC body. The SO-20 package of this IC has 4 GND pins that are not just intended for electrical GND connec-tion, but also to provide a low thermal resistance path between the silicon chip and the PCB heatsink. Given an Rthj-c equal to 15C/W, a maximum of 35C/W are left to the PCB heatsink. This figure is achieved if a minimum of 25cm2 copper area is placed just below the IC body. This area can be the inner GND layer of a multi-layer PCB, or, in a dual layer PCB, an unbroken GND area even on the opposite side where the IC is placed. In both cases, the thermal path between the IC GND pins and the dissipating copper area must exhibit a low thermal resistance. In figure 4 , it is shown a suggested layout for the SO-20 package with a dual layer PCB, where the IC Ground pins and the square dissipating area are thermally connected through 32 vias holes, filled by solder. This arrangement, when L=50mm, achieves an Rthc-a of about 25C/W. Different layouts are possible, too. Basic principles, however, suggest to keep the IC and its ground pins approximately in the middle of the dissipating area; to provide as many vias as possible; to de-sign a dissipating area having a shape as square as possible and not interrupted by other copper traces. Due to presence of an exposed pad connected to GND below the IC body, the PowerSO-20 package has a Rthj-c much lower than the SO-20, only 2C/W. As a result, much lower copper area must be provided to dissipate the same power and minimum of 12cm2 copper area is enough, see figure 5. 16/19 LNBS21 Figure 36 : SO-20 SUGGESTED PCB HEATSINK LAYOUT Figure 37 : PowerSO-20 SUGGESTED PCB HEATSINK LAYOUT 17/19 LNBS21 PowerSO-20 MECHANICAL DATA DIM. A a1 a2 a3 b c D (1) E e e3 E1 (1) E2 G h L N S T 0 10.0 0.80 0 10.90 0 0.40 0.23 15.80 13.90 1.27 11.43 11.10 2.90 0.10 1.10 1.10 10 8 0 0.3937 0.0314 0.0000 0.4291 0.10 mm. MIN. TYP MAX. 3.60 0.30 3.30 0.10 0.53 0.32 16.00 14.50 0 0.0157 0.0090 0.6220 0.5472 0.0500 0.4500 0.4370 0.1141 0.0039 0.0433 0.0433 10 8 0.0039 MIN. inch TYP. MAX. 0.1417 0.0118 0.1299 0.0039 0.0209 0.0013 0.630 0.5710 (1) "D and E1" do not include mold flash or protusions - Mold flash or protusions shall not exceed 0.15mm (0.006") N N a2 A R c a1 DETAIL B E b DETAIL A D e3 e lea d DETAIL A 20 11 a3 DETAIL B E2 T E1 Gage Plan e 0.35 slug - C- S L SEATI NG PLANE GC (COPLANARITY) 1 1 0 PSO20MEC h x 45 0056635 18/19 LNBS21 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 publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. (c) The ST logo is a registered trademark of STMicroelectronics (c) 2002 STMicroelectronics - Printed in Italy - All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco Singapore - Spain - Sweden - Switzerland - United Kingdom - United States. (c) http://www.st.com 19/19 |
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