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ISOM8110: Pspice SIM

Brian Wang0928
Genius 14160 points
Part Number: ISOM8110

Customer is interested in this part and did some SIM results with given Pspice model. 

Please help to confirm if below descriptions are ok.

1. When VIN1 goes up to 14.2V, the X1-OUT is about 193mV. 

2. VAN = VF = 1.42V, is this VF value set in the Pspice model? it is fixed one? 

In the d/s, the max. value is 1.4V. why it's set with 1.42V higher than 1.4V?

3. IF calculation

(14.2-1.42)/5.6K-1.42/820 = 0.55mA. it has the same result with Pspice model/SIM.

4. The Sim result of the IC is about 0.935mA , the calculation result is (3.3-0.19)/10K = 0.31mA. Why there are difference?

5. CTR

CTR = 0.934 / 0.55 = 170% (SIM Result)，CTR = 0.31 / 0.55 = 56% (Calculation Result)，

CTR is set in PSpice Library = 120%. is this fixed value?

There are three different CTR values, it looks there are in 50% to 195% range at IF=0.5mA. Which one is close to real application?

  • +1
    TI__Mastermind 29595 points

    Hello Brian,

    Thanks for reaching out. See my responses below:

    The PSpice model is intended only for use as a behavioral model. Therefore, the model will simulate device behavior, however exact device characteristics should not be treated as true to performance. For real device performance the customer should order samples or an EVM and test.

    Please allow me to review your questions about the model with the team and get back to you tomorrow. 

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Genius 14160 points

    Very Thanks. 

    What customer's expectation is to get the accurate simulation results to understand the output behavior of the device at worst-case scenarios in PLC system.

    DELTA thinks the Pspice model should be more accurate so that they can trust that it is identical with real test results on bench. Could you kindly support it or what workaround you're able to offer?  

    One more question about the OPTO-Emulator. How does the device do that is able to acheive high speed and high BW with SiO2 isolated barrier?

    Regards

    Brian

  • +1 in reply to Brian Wang0928
    TI__Guru 55815 points

    Hi Brian,

    Andrew is currently looking into your questions on PSpice model, he will come back to you on those.

    Regarding opto-emulator speed and bandwidth questions, not using LED enables us to support higher speeds and bandwidths compared to a typical opto-coupler that use LED for data transmission. LEDs are typically slow in switching compared other switching components and require high current for faster switching. Thanks.


    Regards,
    Koteshwar Rao

  • +1 in reply to Koteshwar Rao
    TI__Mastermind 29595 points

    Hi Brian, 

    Thank you for waiting. 

    In short, this model was only intended for very basic behavioral tests and not full device simulation support. To understand complete device characteristics, please perform a bench analysis with our EVM. 

    1. When VIN1 goes up to 14.2V, the X1-OUT is about 193mV.
    2. VAN = VF = 1.42V, is this VF value set in the Pspice model? it is fixed one? In the d/s, the max. value is 1.4V. why it's set with 1.42V higher than 1.4V?
      1. VF is not a fixed value as it is in the datasheet (1.2V (typ), 1.4V (max)). 
      2. This is controlled by VON in the model. 
    3. IF: calculation (14.2-1.42)/5.6K-1.42/820 = 0.55mA. it has the same result with Pspice model/SIM.
      1. The customer’s math looks correct if using Vf of 1.42 V.
    4. The Sim result of the IC is about 0.935mA, the calculation result is (3.3-0.19)/10K = 0.31mA. Why there are difference?
      1. When we simulate as shown. The sim shows exactly 120% of the input at the output, but I did have to adjust the output resistor to be 100 ohms to see the current properly – with 10k the device rails out with a very small current flowing.
      2.  
    5. CTR: CTR = 0.934 / 0.55 = 170% (SIM Result), CTR = 0.31 / 0.55 = 56% (Calculation Result), CTR is set in PSpice Library = 120%. is this fixed value? There are three different CTR values, it looks there are in 50% to 195% range at IF=0.5mA. Which one is close to real application?
      1. CTR is fixed to 120% in the simulation, and we expect CTR to be close to the typical value in a real application as well. Please note that the datasheet shows CTR variance getting tighter as IF increases (measured at IF 0.5mA, 2mA and 5mA) this will not be reflected in the model.
      2. Other devices in the ISOM811x family will have different CTR ranges as indicated in the datasheet. 

    I hope this helps.

    Best,
    Andrew

  • 0 in reply to Andrew J
    TI__Genius 14160 points

    Thanks. Please find here for following question in line as Green marked. 

    1. When VIN1 goes up to 14.2V, the X1-OUT is about 193mV. 
    2. VAN = VF = 1.42V, is this VF value set in the Pspice model? it is fixed one? In the d/s, the max. value is 1.4V. why it's set with 1.42V higher than 1.4V?[Question Oct/5] Why 1.42V is set in SIM model, In the d/s the VF,max is 1.4, isn't?  
      1. VF is not a fixed value as it is in the datasheet (1.2V (typ), 1.4V (max)). 
      2. This is controlled by VON in the model. 
    3. IF: calculation (14.2-1.42)/5.6K-1.42/820 = 0.55mA. it has the same result with Pspice model/SIM.
      1. The customer’s math looks correct if using Vf of 1.42 V. [Question Oct/5] When CTR = 120% and IC,max = 3.3V/10K =0.33mA, IF = 0.33/CTR =0.275mA, VF =1.42V. VIN1 shuld be (1.42V/820 +0.275mA)x5.6K ohm =11.2V; as a result when VIN1 reachs to 11.2V, the X1-OUT is LOW state, correct? Why 1.42V is set here?
    4. The Sim result of the IC is about 0.935mA, the calculation result is (3.3-0.19)/10K = 0.31mA. Why there are difference?
      1. When we simulate as shown. The sim shows exactly 120% of the input at the output, but I did have to adjust the output resistor to be 100 ohms to see the current properly – with 10k the device rails out with a very small current flowing.
      2. [Question Oct/5] Regarding to the pull-up resistor of 10K Ohm, it looks the device can accept 100Ohm in pull-up resistor, and 10K is not accepted, right? 
      3. [Question Oct/5] What's the minimum value suggestion of this pull-up resistor to meet IC's requirement?  
      4.  
    5. CTR: CTR = 0.934 / 0.55 = 170% (SIM Result), CTR = 0.31 / 0.55 = 56% (Calculation Result), CTR is set in PSpice Library = 120%. is this fixed value? There are three different CTR values, it looks there are in 50% to 195% range at IF=0.5mA. Which one is close to real application?
      1. CTR is fixed to 120% in the simulation, and we expect CTR to be close to the typical value in a real application as well. Please note that the datasheet shows CTR variance getting tighter as IF increases (measured at IF 0.5mA, 2mA and 5mA) this will not be reflected in the model.
      2. Other devices in the ISOM811x family will have different CTR ranges as indicated in the datasheet. 
      3. [Oct/5] For the SIM model support, we'll discuss on the other mail. 

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    TI__Mastermind 29595 points

    Hi Brian,

    Thank you for the follow up.

    Brian Wang0928 said:
    [Question Oct/5] Why 1.42V is set in SIM model, In the d/s the VF,max is 1.4, isn't?  

    I have received some clarification from the team here. We chose to use the worst-case value for the device family (1.5V) as shown in the below screen capture. This is set in the model as 1.49V in line 71 and can be changed to 1.39V to match the ISOM8110's max. We are still looking into the reason why 1.42 is the number.

     

    .MODEL IN_DIODE VSWITCH VON = {1.49} VOFF = {1.35} RON = 1 ROFF = 5E6

    Brian Wang0928 said:
     [Question Oct/5] When CTR = 120% and IC,max = 3.3V/10K =0.33mA, IF = 0.33/CTR =0.275mA, VF =1.42V. VIN1 shuld be (1.42V/820 +0.275mA)x5.6K ohm =11.2V; as a result when VIN1 reachs to 11.2V, the X1-OUT is LOW state, correct? Why 1.42V is set here?

    The diode will not turn on when IF < 0.500mA. Based on your calculations the 10k resistor is too much and not allowing the diode to turn on. The input current of 0.275mA is not enough to turn the input diode on. 

    Brian Wang0928 said:
    • [Question Oct/5] Regarding to the pull-up resistor of 10K Ohm, it looks the device can accept 100Ohm in pull-up resistor, and 10K is not accepted, right? 
    • [Question Oct/5] What's the minimum value suggestion of this pull-up resistor to meet IC's requirement?  

    The pull-up resistor max size should be such that the Rpull-up = VCC / (0.500mA*CTR) or 5.5kohms (assuming 3.3V and 120% CTR). The minimum pull-up resistor value is limitid by the device current limit (50mA) Rmin = 3.3V/50mA = 66ohms.  

    Brian Wang0928 said:
    [Oct/5] For the SIM model support, we'll discuss on the other mail. 

    We will discuss further support over email, and I can continue to answer questions about the TI model here as needed. Let me know when the questions are sufficiently answered. 

    Best,
    Andrew