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PHASE LOCKED LOOP APPLICATIONSRAMP GENERATORS (566)Figure 8-62 shows how the 566 can be wired as a positiveor negative ramp generator. I n the positive ramp generator,the external transistor driven by the pin 3 output rapidlydischarges C1 at the end of the charging period so thatcharging can resume instantaneously. The pnp transistorlikewise rapidly charges the timing capacitor C1 at the endof the discharge period. Because the circuits are reset soquickly, the temperature stability of the ramp generator isexcellent. The period T is 1/2fo where fo is the 566 freerunningfrequency in normal operation. Therefore,1 RTC1V+7 = - =2fo 5(V+ - V c)where V c is the bias voltage 7 pin 5 and RT is the totalresistance between pin 6 and V+. Note that a short pulse isavailable at pin 3. (Placing collector resistance in serieswith the external transistor collector will lengthen thepulse.)SAWTOOTH AND PULSE GENERATOR (566)Figure 8-63 shows how pin 3 output can be used toprovide different charge and discharge currents for C1 sothat a sawtooth output is available at pin 4 and a pulse atpin 3. The pnp transistor should be well saturated topreserve good temperature stability. The charge anddischarge times may be estimated by using the formulaRTC1V+7 =5(V+ - Vc )where RT is the combined resistance between pin 6 andV+ for the interval considered.v+POSITIVE SAWTOOTH ANDPULSE GENERATORNEGATIVE RAMP GENERATORv+1.5K1.5Kvc10K,....&..--...... I--I--~A/'v SAWTOOTH~PULSEvc10KFigure 8-63aFigure 8-62aPOSITIVE RAMP GENERATORv+NEGATIVE SAWTOOTH ANDPULSE GENERATORv+20K1.5K1.5K5 6 8 4566~TOOTH4.7K10K~LSE22KFigure 8-62bFigure 8-63b62