Other Parts Discussed in Thread: SN74HC14,
Tool/software:
I believe the spice model for the SC74AC14 (as seen on the product page) has a critical flaw: the values for `RA` and `RB` effectively short the input pins to ground.
* When I attempt to simulate a Schmitt inverter oscillator with the SC74HC14 model, it works as expected.
* When I use the SC74AC14 instead, the inputs suck all the loopback current, my capacitor doesn't charge, and the part draws kA of current on its VCC.
.title KiCad schematic .include "SN74AC14.cir" .save all .probe alli .probe p(XU1) .probe p(R2) .probe p(C1) .probe p(V1) .tran .05u 2m XU1 /out /in +3V3 GND SN74AC14 R2 /in /out 1k C1 /in GND 100p V1 +3V3 GND DC 3.3 .end
If I diff SN74HC14.cir and SN74AC14.cir, I see the former sets the parameters RA and RB to 240000000 (aka 2.4e+07). The latter sets those parameters to 2.5e-05. I'm unsure of the correct value, but simulation succeeds if I remove the minus sign from the exponent.
$ diff -u SN74HC14.cir SN74AC14.cir
--- SN74HC14.cir 2020-01-13 09:13:22
+++ SN74AC14.cir 2020-01-13 09:05:28
@@ -1,5 +1,5 @@
********************************************************************************
-* SN74HC14.cir
+* SN74AC14.cir
* 2.0
* 2019-11-14 00:00:00
* Texas Instruments Incorporated.
@@ -30,36 +30,36 @@
*
*
********************************************************************************
-* SN74HC14
+* SN74AC14
********************************************************************************
-.SUBCKT SN74HC14 Y A VCC AGND
-XU1 Y A VCC VCC AGND LOGIC_GATE_2PIN_OD_HC_1i_NAND_PP_ST_SN74HC14
+.SUBCKT SN74AC14 Y A VCC AGND
+XU1 Y A VCC VCC AGND LOGIC_GATE_2PIN_OD_AHC_1i_NAND_PP_ST_SN74AC14
.ENDS
-.SUBCKT LOGIC_GATE_2PIN_OD_HC_1i_NAND_PP_ST_SN74HC14 OUT A B VCC GND
+.SUBCKT LOGIC_GATE_2PIN_OD_AHC_1i_NAND_PP_ST_SN74AC14 OUT A B VCC GND
.PARAM VCC_ABS_MAX = 7
.PARAM VCC_MAX = 6
-.PARAM RA = 240000000
-.PARAM RB = 240000000
-.PARAM CA = 1e-11
-.PARAM CB = 1e-11
-.PARAM ROEZ = 5000
+.PARAM RA = 2.4e-05
+.PARAM RB = 2.4e-05
+.PARAM CA = 2.8e-12
+.PARAM CB = 2.8e-12
+.PARAM ROEZ = 2000
.PARAM COEZ = 3e-12
RA A GND {RA}
RB B GND {RB}
...
