EL7457 model bug? or missing parasitics needed?

QSPICE
1

Hi,

Context:
I am in the process of designing a PCB which contains a 2-stage CMOS driver subcircuit.
I picked up the same subcircuit from an existing design with the intention of tweaking some of the passive components. This subcircuit (in the attached KiCad schematic) actually works (on the physical PCB) as I was able to verify using the test points.

Simulation Behavior:
I am trying to simulate this in QSPICE in the QSPICE schematic (cannot attach since I am new user, please help). It seems that without connecting a resistive load there is no pulse on the output of the EL7457. I can live with that at the output of the 2nd stage. However, with regard for the 1st stage, I would rather have all the components connected to the trace between its output and the input of the 2nd stage match what is going on with the actual design (no extra resistive load) with an inclusion of parasitics that is still practical. The problem: X2.INA is not behaving as a resistive so there is no pulse at X1.OUTA.

Workaround attempts:

  • I tried some solutions that model the trace parasitics as transmission lines. The problem is that when the transmission line is terminated correctly (case of T1) it works as a voltage divider. Also why should I assume that these terminations actually reflect the input and output impedances of the ICs. For these reasons (and perhaps others) I don’t feel that a transmission line modeling of the parasitics makes sense. Please correct me if I am wrong and you have the time and patience.
  • Aside from that I can use a simple resistor connected to the trace and to GND, but why should I do this when I know that I am drawing current through it and this does not reflect actual parasitics.

Please let me know what I am doing wrong in QSPICE?

Schematic_KiCad_2_stage_CMOS
Schematic_KiCad_2_stage_CMOS1423×494 45.8 KB

2

Hi, haplessEE.

The schematic would, of course, help. See this for info about trust levels to upload.

–robert

4 
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      «pin (-400,100) (0,0) 1 0 0 0x0 -1 "L1"»
      «pin (-400,-100) (0,0) 1 0 0 0x0 -1 "L2"»
      «pin (400,100) (0,0) 1 0 0 0x0 -1 "R1"»
      «pin (400,-100) (0,0) 1 0 0 0x0 -1 "R2"»
    »
  »
  «component (100,-4900) 2 0
    «symbol R1
      «type: R»
      «description: Resistor(UK Style Symbol)»
      «shorted pins: false»
      «line (0,-200) (0,-150) 0 0 0x1000000 -1 -1»
      «line (0,150) (0,200) 0 0 0x1000000 -1 -1»
      «rect (50,-150) (-50,150) 0 0 0 0x1000000 0x2000000 -1 0 -1»
      «text (50,0) 1 110 0 0x1000000 -1 -1 "R6"»
      «text (-50,0) 1 109 0 0x1000000 -1 -1 "1000"»
      «pin (0,-200) (0,0) 1 64 0 0x0 -1 "+"»
      «pin (0,200) (0,0) 1 64 0 0x0 -1 "-"»
    »
  »
  «component (2500,900) 2 0
    «symbol R1
      «type: R»
      «description: Resistor(UK Style Symbol)»
      «shorted pins: false»
      «line (0,-200) (0,-150) 0 0 0x1000000 -1 -1»
      «line (0,150) (0,200) 0 0 0x1000000 -1 -1»
      «rect (50,-150) (-50,150) 0 0 0 0x1000000 0x2000000 -1 0 -1»
      «text (50,0) 1 110 0 0x1000000 -1 -1 "R7"»
      «text (-50,0) 1 109 0 0x1000000 -1 -1 "82"»
      «pin (0,-200) (0,0) 1 64 0 0x0 -1 "+"»
      «pin (0,200) (0,0) 1 64 0 0x0 -1 "-"»
    »
  »
  «component (3200,500) 0 0
    «symbol R1
      «type: R»
      «description: Resistor(UK Style Symbol)»
      «shorted pins: false»
      «line (0,-200) (0,-150) 0 0 0x1000000 -1 -1»
      «line (0,150) (0,200) 0 0 0x1000000 -1 -1»
      «rect (50,-150) (-50,150) 0 0 0 0x1000000 0x2000000 -1 0 -1»
      «text (50,150) 1 7 0 0x1000000 -1 -1 "R13"»
      «text (50,-150) 1 7 0 0x1000000 -1 -1 "1K"»
      «pin (0,-200) (0,0) 1 64 0 0x0 -1 "+"»
      «pin (0,200) (0,0) 1 64 0 0x0 -1 "-"»
    »
  »
  «net (-300,-1900) 1 13 0 "GND"»
  «net (-1000,-1900) 1 13 0 "GND"»
  «net (-2000,-200) 1 13 0 "GND"»
  «net (-2000,1300) 1 13 0 "GND"»
  «net (3900,1200) 1 13 0 "GND"»
  «net (4900,-1900) 1 13 0 "GND"»
  «net (7400,-1900) 1 13 0 "GND"»
  «net (5700,-1900) 1 13 0 "GND"»
  «net (-5000,-3800) 1 13 0 "GND"»
  «net (-6900,-3400) 1 13 0 "GND"»
  «net (-200,-3800) 1 13 0 "GND"»
  «net (1200,2300) 1 7 0 "out1"»
  «net (7200,2200) 1 7 0 "out2"»
  «net (4700,-5200) 1 13 0 "GND"»
  «net (3200,-3700) 1 13 0 "GND"»
  «net (4700,-3700) 1 13 0 "GND"»
  «net (-1800,-5200) 1 13 0 "GND"»
  «net (-300,-5200) 1 13 0 "GND"»
  «net (3200,100) 1 13 0 "GND"»
  «junction (7200,900)»
  «junction (6300,1900)»
  «junction (6300,-800)»
  «junction (5700,-1700)»
  «junction (5500,-2900)»
  «junction (5500,-4400)»
  «junction (4900,1900)»
  «junction (4900,1300)»
  «junction (4700,-3400)»
  «junction (4700,-4900)»
  «junction (4000,-4400)»
  «junction (4000,-4900)»
  «junction (3200,900)»
  «junction (3200,-3400)»
  «junction (2500,-2900)»
  «junction (2500,-4400)»
  «junction (1200,900)»
  «junction (1100,-300)»
  «junction (500,-4400)»
  «junction (300,-800)»
  «junction (300,-1700)»
  «junction (-200,-2900)»
  «junction (-300,-500)»
  «junction (-300,-1700)»
  «junction (-300,-4900)»
  «junction (-1000,1900)»
  «junction (-1000,1300)»
  «junction (-5000,-2900)»
  «junction (-5000,-3700)»
  «wire (-500,900) (-2000,900) "N01"»
  «wire (-300,-1700) (-300,-1900) "GND"»
  «wire (600,-300) (600,-100) "N02"»
  «wire (300,-800) (-1000,-800) "N02"»
  «wire (-1000,-1400) (-1000,-1900) "GND"»
  «wire (600,1500) (600,1900) "GND"»
  «wire (600,1900) (1400,1900) "GND"»
  «wire (1400,1900) (1400,-1700) "GND"»
  «wire (300,-1700) (-300,-1700) "GND"»
  «wire (-300,-500) (-300,-1700) "GND"»
  «wire (-2000,900) (-2000,700) "N01"»
  «wire (-2000,300) (-2000,-200) "GND"»
  «wire (-500,1300) (-1000,1300) "N03"»
  «wire (-1000,1300) (-1000,1900) "N03"»
  «wire (-1000,1900) (300,1900) "N03"»
  «wire (300,1900) (300,1500) "N03"»
  «wire (-1000,1900) (-1000,2400) "N03"»
  «wire (-1000,2400) (-2000,2400) "N03"»
  «wire (-2000,2400) (-2000,1900) "N03"»
  «wire (-2000,1500) (-2000,1300) "GND"»
  «wire (-1000,200) (-1000,1300) "N03"»
  «wire (-1000,-200) (-1000,-500) "GND"»
  «wire (-1000,-500) (-300,-500) "GND"»
  «wire (-300,-100) (-300,-500) "GND"»
  «wire (300,-1000) (300,-800) "N02"»
  «wire (300,-1400) (300,-1700) "GND"»
  «wire (1400,-1700) (300,-1700) "GND"»
  «wire (7200,900) (7400,900) "out2"»
  «wire (6600,1500) (6600,1900) "N04"»
  «wire (5500,1300) (4900,1300) "N04"»
  «wire (4900,1900) (6300,1900) "N04"»
  «wire (6300,1900) (6300,1500) "N04"»
  «wire (4900,1900) (4900,2400) "N04"»
  «wire (4900,2400) (3900,2400) "N04"»
  «wire (3900,2400) (3900,1800) "N04"»
  «wire (3900,1400) (3900,1200) "GND"»
  «wire (6600,1900) (6300,1900) "N04"»
  «wire (4900,200) (4900,1300) "N04"»
  «wire (4900,-1400) (4900,-1900) "GND"»
  «wire (6600,-300) (6600,-100) "N05"»
  «wire (7400,900) (7400,300) "out2"»
  «wire (7400,-100) (7400,-1900) "GND"»
  «wire (4900,1300) (4900,1900) "N04"»
  «wire (6300,-800) (4900,-800) "N05"»
  «wire (4900,-800) (4900,-1000) "N05"»
  «wire (4900,-200) (4900,-500) "GND"»
  «wire (4900,-500) (5700,-500) "GND"»
  «wire (5700,-1700) (5700,-500) "GND"»
  «wire (5700,-1700) (6300,-1700) "GND"»
  «wire (6300,-1000) (6300,-800) "N05"»
  «wire (6300,-1400) (6300,-1700) "GND"»
  «wire (5700,-1900) (5700,-1700) "GND"»
  «wire (5700,-100) (5700,-300) "N02"»
  «wire (1100,-300) (600,-300) "N02"»
  «wire (-6900,-3400) (-6900,-3100) "GND"»
  «wire (-6900,-3100) (-6500,-3100) "GND"»
  «wire (-5000,-2900) (-3700,-2900) "N06"»
  «wire (-5400,-3100) (-5700,-3100) "GND"»
  «wire (-5000,-3700) (-5000,-3600) "GND"»
  «wire (-6500,-2900) (-7100,-2900) "N07"»
  «wire (-5400,-3100) (-5400,-3700) "GND"»
  «wire (-5400,-3700) (-5000,-3700) "GND"»
  «wire (-5000,-3800) (-5000,-3700) "GND"»
  «wire (-5000,-3200) (-5000,-2900) "N06"»
  «wire (-5700,-2900) (-5000,-2900) "N06"»
  «wire (-200,-2900) (1400,-2900) "N08"»
  «wire (-200,-2900) (-200,-3200) "N08"»
  «wire (-600,-2900) (-200,-2900) "N08"»
  «wire (-200,-3800) (-200,-3600) "GND"»
  «wire (1200,900) (1100,900) "out1"»
  «wire (5700,-300) (1100,-300) "N02"»
  «wire (1100,-800) (300,-800) "N02"»
  «wire (6300,-800) (7100,-800) "N05"»
  «wire (7100,-300) (6600,-300) "N05"»
  «wire (300,-100) (300,-800) "N02"»
  «wire (1100,-800) (1100,-300) "N02"»
  «wire (6300,-100) (6300,-800) "N05"»
  «wire (7100,-800) (7100,-300) "N05"»
  «wire (-1000,-1000) (-1000,-800) "N02"»
  «wire (1200,2300) (1200,2400) "out1"»
  «wire (7200,2200) (7200,2400) "out2"»
  «wire (7100,900) (7200,900) "out2"»
  «wire (1200,900) (1200,2300) "out1"»
  «wire (7200,900) (7200,2200) "out2"»
  «wire (5500,-4400) (6400,-4400) "N09"»
  «wire (4700,-4900) (4900,-4900) "GND"»
  «wire (4700,-5200) (4700,-4900) "GND"»
  «wire (5300,-4900) (5500,-4900) "N09"»
  «wire (5500,-4900) (5500,-4400) "N09"»
  «wire (2600,-4900) (2500,-4900) "N09"»
  «wire (2500,-4900) (2500,-4400) "N09"»
  «wire (2500,-4400) (2100,-4400) "N09"»
  «wire (4000,-4900) (4700,-4900) "GND"»
  «wire (3000,-4900) (4000,-4900) "GND"»
  «wire (4000,-4400) (5500,-4400) "N09"»
  «wire (4000,-4400) (4000,-4500) "N09"»
  «wire (2500,-4400) (4000,-4400) "N09"»
  «wire (3200,-3400) (3200,-3100) "GND"»
  «wire (3200,-3100) (3600,-3100) "GND"»
  «wire (4700,-3100) (4400,-3100) "GND"»
  «wire (4700,-3400) (4700,-3100) "GND"»
  «wire (5500,-2900) (6400,-2900) "N10"»
  «wire (3000,-3400) (3200,-3400) "GND"»
  «wire (3200,-3700) (3200,-3400) "GND"»
  «wire (4700,-3400) (4900,-3400) "GND"»
  «wire (4700,-3700) (4700,-3400) "GND"»
  «wire (5300,-3400) (5500,-3400) "N10"»
  «wire (5500,-3400) (5500,-2900) "N10"»
  «wire (4400,-2900) (5500,-2900) "N10"»
  «wire (2600,-3400) (2500,-3400) "N11"»
  «wire (2500,-3400) (2500,-2900) "N11"»
  «wire (3600,-2900) (2500,-2900) "N11"»
  «wire (2500,-2900) (2100,-2900) "N11"»
  «wire (-1800,-4600) (-1400,-4600) "GND"»
  «wire (-300,-4600) (-600,-4600) "GND"»
  «wire (-300,-4900) (-300,-4600) "GND"»
  «wire (500,-4400) (1400,-4400) "N12"»
  «wire (-1800,-5200) (-1800,-4600) "GND"»
  «wire (-300,-4900) (-100,-4900) "GND"»
  «wire (-300,-5200) (-300,-4900) "GND"»
  «wire (300,-4900) (500,-4900) "N12"»
  «wire (500,-4900) (500,-4400) "N12"»
  «wire (-600,-4400) (500,-4400) "N12"»
  «wire (-1400,-4400) (-2900,-4400) "N13"»
  «wire (-7500,-2900) (-8000,-2900) "N14"»
  «wire (-1000,-2900) (-2900,-2900) "N15"»
  «wire (1200,900) (2300,900) "out1"»
  «wire (3200,900) (5500,900) "N16"»
  «wire (2700,900) (3200,900) "N16"»
  «wire (3200,300) (3200,100) "GND"»
  «wire (3200,900) (3200,700) "N16"»
  «text (-3500,-1200) 1 7 0 0x1000000 -1 -1 ".tran 40µ"»
  «text (-3500,-1400) 1 7 0 0x1000000 -1 -1 ".plot V(out1) V(out2)"»
»
5

Thanks @RDunn,

In accordance with the forum entry you referred to, I uploaded the code of the schematic.

Note that the embedded EL7457 symbol in the schematic is translated from the SPICE symbol provided by RENESAS.

6

Are you referring to model download from EL7457 - 40MHz Non-Inverting Quad CMOS Driver | Renesas
This is simulation result from Renesas EL7457C SPICE model, but series resistor between symbols is not required.

example.EL7457C.CMOS-Driver.qsch (40.6 KB)
Renesas-EL7457C.qsym (3.8 KB)

image
image1489×475 72.2 KB

7

Thanks @KSKelvin,

Yes, we are using the same model. I used Mike’s explanation in the youtube video to generate mine from the symbol that I downloaded from the same RENESAS webpage you refer to. I think you added a drawing from the datasheet which makes the symbol look nicer in the schematic. I am a beginner so I am only trying to get my subcircuits to function in QSPICE.

I ran your configuration and I can see that it works.

However you have configured the circuit differently compared to the .qsch which I uploaded.
I slightly adjusted your schematic just to change the voltage levels on the 1st stage to match my subcircuit and now it no longer works again (I detached the 2nd stage since clearly the problem is in the configuration of the single IC). Why is that? The levels are all still within the limits in the table (I checked the datasheet before asking of course.)

example.EL7457C.CMOS-Driver_edited1
example.EL7457C.CMOS-Driver_edited11501×927 59.5 KB

8

The schematic you shown with first stage VH to GND, OUTA high level is 0V? And second stage has nothing connect to VIN. Is this screen capture correct?

9

Hi @KSKelvin,

Yes this is intentional. I want VH for 1st stage to be 0V. I just disconnected the 2nd stage to observe what is going on with the 1st stage only.

10

If VH=0V, OUTA1 high level is 0V. This looks normal.

image
image1453×545 71.2 KB

You know that INA (or VIN) must be larger than 2V as logic HIGH for input, right?

image
image1239×294 31.2 KB

11

In your uploaded schematic, the GND of the second stage is connected to -4.4V. It is possible that the model from Renesas does not account for this operating condition. Is this your physical connection, and does it actually work?
Simulation model may not cover connections that fall outside its intended use. In general, the GND pins would generally be expected to be connected together to same the same ground or same floating ground.

image
image956×407 32.3 KB