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LM1893 Datasheet(PDF) 8 Page - National Semiconductor (TI) |
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LM1893 Datasheet(HTML) 8 Page - National Semiconductor (TI) |
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8 / 24 page  Application Information (Continued) Recommended Purpose Effect of making the component value Notes Value Smaller Larger CO 560 pF Together CO and RO Increases FO Decreases FO g 5% NPO ceramic Use low TC RO 62 kX set ICO FO Increases FO Decreases FO 2 k pot and 56 k fixed R k 56 k not recommended l 76 k not recommended Poor FO TC with k5 6kRO CF 0047 mF PLL loop filter pole Less noise immune higher More noise immune lower Depending on RF value and fDATA more PLL stability fDATA less PLL stability FO PLL unstable with large RF 33 kX PLL loop filter zero PLL less stable allows PLL more stable allows CF See Apps Info CF less CF Less ringing more CF More ringing and RF values not critical CC 022 mF Couples FO to line Low TX line amplitude Drives lower line Z t 250 V non-polar Use 2CC CC and T1 low-pass Less 60 Hz T1 current More 60 Hz T1 current on hot and neutral for max attenuates 60 Hz Less stored charge More stored charge line isolation safety CQ 0033 mF Tank matches line Z Tank FO up or increase Tank FO down or decrease 100 V nonpolar low TC g10% bandpass filters L of T1 for constant FO L of T1 for constant FO High large-signal Q needed T1 Use isolates from line Smaller L higher FO or Larger L lower FO or Optimize for low FO line recommended and attenuates increase CC decreased FO decrease CC increased FO pull with control of FO TC XFMR transients line pull line pull and Q CA 01 mF ALC pole Noise spikes turn ALC off Slower ALC response RA optional ALC stable RA 10 kX ALC zero Less stable ALC More stable ALC for CAt100 pF CL 0047 mF Limiter 50 kHz pole Higher pole F more 60 Hz Lower pole F less 60 Hz Any reasonably low TC cap 60 Hz rejection reject FO attenuation reject more noise BW 300 pF guarantees stability CM 047 mF Holds RX path VOS Less noise immune shorter More noise immune longer Low leakage g20% cap VOS hold faster VOS aqui- VOS hold slower VOS aqui- Scale with fDATA sition shorter preamble sition longer preamble CI 0047 mF Rejects short pulses Less impulse reject less More impulse reject more CI charge time bit nom like impulse noise delay more pulse jitter delay less pulse jitter Must be k1 bit worst-case RC 10 kX Open-col pull-up Less available sink I Less available source I RCt15 kX on 56 V RZ 12 kX 56 V Zener bias Larger shunt current Smaller shunt current 1kIZk30 mA recommended more chip dissipation less Va current draw (Chip power-up needs 56 V) ZT t44 V BV Transient clamp ZT failure higher series ZT costly lower series Recommend Zener rated k 60 V peak R-excess peak V Zener R gives enhanced for t500 W for 1 ms and chip damage transient clamp less ruggedness more ruggedness RT 47 X Transient I limit Damage ZT pull up Va Excessive TX attenuation Carbon comp recommended DT t44V BV Over-drive Clamp Failure on Transient Costly IRF 11DQ05 or 1N5819 RB 180 X Base bleed Faster lower THD IO Inadequate turn-off speed Boost optional QB F(b3 dB) QB Power NPN Boost gain device Excessive TJ and VSAT More rugged but costly of l200 MHz RB l 24 Ohm RG 11 X Current setting R More IO need higher hfe Less IO lower min hfe IOe70 (10aRG)RG mApp CB t47 mF Supply bypass Transients destroy chip Less supply spike Va never over abs max ZA 51V Stop ALC charge Excess ALC ALC RX charging ZA optional - 51V in RX mode current flow not inhibited over TJ g 20% low leakage type FIGURE 5 A quick explanation of the external component function using the circuit of Figure 4 Values given are for Va e 18 V FO e 125 kHz fDATA e 360 Baud (180 Hz) using a 115 V 60 Hz power line Component Selection Assuming the circuit of Figure 4 is used with something oth- er than the nominal 125 kHz carrier frequency 180 Hz data rate 18V supply voltage etcetera the component values listed in Figure 5 will need changing This section will help direct the CCT designer in finding the required component values with emphasis placed on look-up tables and charts It is assumed that the designer has selected values for carrier center frequency FO data rate fDATA supply voltage Va power line voltage VL and power line frequency FL Ifone or more of those parameters is not defined one may read the data sheet and make an educated guess Maxims to keep in mind based on CCT electrical perform- ance considerations only are 1) the higher the FO the bet- ter 2) the lower the maximum data rate the better and 3) the more time and frequency filtering the better Use Figure 5 as a quick reference to the external compo- nent function THE TRANSMITTER CO Central to chip operation is the low TC of FO emitter-cou- pled oscillator With proper CO the FO of the 2VBE ampli- tude triangle-wave oscillator output may vary from near DC to above 300 kHz While CO may have any value CO should 8 |
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