* TX Path - R2 Sweep at Worst-Case CTR (Igain=0.5m ~ PC817A min)
* Finding optimal R2 for 3.3V ESP32 design
* PC817 pin order: 1=Anode, 2=Cathode, 3=Collector, 4=Emitter

.param R2val 470

V_BAT V12 0 12
V_MCU VCC 0 3.3
V_TX TX 0 PWL(0u 0 199.5u 0 200u 3.3 512u 3.3 512.5u 0 2000u 0)
R_PULL V12 IBUS 4.7k
C_BUS IBUS 0 100p
R5 TX R5_R3 470
R3 R5_R3 Q1B 10k
Q1 Q1C Q1B 0 BC547B
R2 VCC U2_A {R2val}
XU2 U2_A Q1C IBUS 0 PC817 Igain=0.5m
R1_RX IBUS U1_A 2k
XU1 U1_A 0 VCC RX PC817 Igain=0.5m
R4_RX RX 0 1k

.subckt PC817 1 2 3 4
R1 N003 2 2
D1 1 N003 LD
G1 3 N004 N003 2 {Igain}
C1 1 2 18p
Q1 3 N004 4 [4] NP
.model LD D(Is=1e-20 Cjo=18p)
.model NP NPN(Bf=1200 Vaf=140 Ikf=100m Rc=1 Cjc=19p Cje=7p Cjs=7p C2=3e-15)
.ends PC817

.model BC547B NPN(IS=2.39E-14 NF=1.008 ISE=3.545E-15 NE=1.541 BF=294.3 IKF=0.1357 VAF=63.2 NR=1.004 ISC=6.272E-14 NC=1.243 BR=7.946 IKR=0.1144 VAR=25.9 RB=1 IRB=1.00E-06 RBM=1 RE=0.4683 RC=0.85 XTB=0 EG=1.11 XTI=3 CJE=1.358E-11 VJE=0.65 MJE=0.3279 TF=4.391E-10 XTF=120 VTF=2.643 ITF=0.7495 PTF=0 CJC=3.728E-12 VJC=0.3997 MJC=0.2955 XCJC=0.6193 TR=1.00E-32 CJS=0 VJS=0.75 MJS=0.333 FC=0.9579 Vceo=45 Icrating=100m mfg=NXP)

.step param R2val list 100 150 220 270 330 390 470
.tran 0 1500u 0 0.5u
.meas tran IBUS_LOW MIN V(IBUS)
.meas tran IBUS_HIGH MAX V(IBUS)
.meas tran LED_CURRENT MAX I(R2)
.meas tran BUS_RISE TRIG V(IBUS) VAL=0.5 RISE=1 TARG V(IBUS) VAL=3.5 RISE=1
.backanno
.end