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LM7480-Q1: Protection against ISO7637-2 and ISO 16750-2

william Washington
Prodigy 40 points
Part Number: LM7480-Q1
Other Parts Discussed in Thread: LM74900, LM74900-Q1, TINA-TI, LM74800-Q1,

My first question relates to the M74800EVM-CS evaluation module - on Figure 3-1 it says 2A max current but there is no indication why this is the max current since the FET is rated at 34A, can you please explain why there is a 2A max current?

Second Question:
In Clamped mode, with a 200V surge VS is clamped to ~56V + by D4 and VOUT is set at ~33V(falling nominal) by R6/R4. OUT will be less than 1V higher that VOUT (drop across Q2) giving an OUT to VS of greater than ~+22V. Absolute maximum  OUT to VS is stated as -65 to +16.5V which appears to be exceeded in the scenario. Can you please explain?

Third Question - what is the function of D6?

I could see D6 providing protection to OUT/VS if it was a zener, but as a rectifier I do not see the purpose of it

Fourth Question
It is not stated anywhere that I can see, but is the LM74801 not suitable for the CS configuration? and also the LM74900 is probably not useable in the CS configuration because of the lower VOUT to VS (-65 to +5) positive maximum.

I am looking for un-suppressed load dump protection for 12V and 24V vehicle systems which must provide load dump ride through - ie continued operation during the load dump plus protection against the full range of transients and other conditions included in ISO7637-2 and ISO 16750-2.  So for Load dump that means input up to ~202V with over voltage continuing for ~350ms.
Normal load current is expected to be around 1.5 to 2A, but going up to ~7 or 8A on occasions.
I also therefore wanted an over current shut down at ~9.5A as a safety feature.

  • 0
    TI__Guru 57737 points

    Hi William,

    Please find my response inline  below,

    My first question relates to the M74800EVM-CS evaluation module - on Figure 3-1 it says 2A max current but there is no indication why this is the max current since the FET is rated at 34A, can you please explain why there is a 2A max current?

    The Rds(on) of Q1 - 200V FET is very high and the power loss in it increases drastically with increase in load current. You can test the EVM only upto 2A at higher temperatures but you can go up to 5A for testing at room temperature. 

    Second Question:
    In Clamped mode, with a 200V surge VS is clamped to ~56V + by D4 and VOUT is set at ~33V(falling nominal) by R6/R4. OUT will be less than 1V higher that VOUT (drop across Q2) giving an OUT to VS of greater than ~+22V. Absolute maximum  OUT to VS is stated as -65 to +16.5V which appears to be exceeded in the scenario. Can you please explain?

    OUT-VS = 33V - 56V = -23V is within the range of -65V to +16.5V

    Third Question - what is the function of D6?

    I could see D6 providing protection to OUT/VS if it was a zener, but as a rectifier I do not see the purpose of it

    D6 is used to provide low impedance path between power supply and VS pin when HGATE is high. Without D6, there is a 10kohms resistance between power supply and VS pin. D6 is especially useful when low voltage operation (VS<5V) is required where the Iq is very high and the drop across the 10k will be significantly high.   

    Fourth Question
    It is not stated anywhere that I can see, but is the LM74801 not suitable for the CS configuration? and also the LM74900 is probably not useable in the CS configuration because of the lower VOUT to VS (-65 to +5) positive maximum.

    LM74801-Q1 can be used in CS topology.

    LM74900-Q1 cannot be used in CS topology due to the device internal architecture. 

    I am looking for un-suppressed load dump protection for 12V and 24V vehicle systems which must provide load dump ride through - ie continued operation during the load dump plus protection against the full range of transients and other conditions included in ISO7637-2 and ISO 16750-2.  So for Load dump that means input up to ~202V with over voltage continuing for ~350ms.
    Normal load current is expected to be around 1.5 to 2A, but going up to ~7 or 8A on occasions.
    I also therefore wanted an over current shut down at ~9.5A as a safety feature.

    We do have a device which will be released in a couple of months which can work in CS topology and also has over current and short circuit protection. 

  • 0 in reply to Praveen GD
    Prodigy 40 points

    Thank you Praveen,
    In my second question I was subtracting the wrong way.
    Your response has been very helpful.

    I am very interested in this new device to be released in a couple of months, are you able, please to share some more information?
    Part number? preliminary specification/data sheet? expected release date?

    Can you also please recommend an overcurrent protection chip to use in conjunction with an LM74800?

  • 0 in reply to william Washington
    TI__Guru 57737 points

    Hi William,

    I will be able to share the below information with you only under NDA.

    • Part number? preliminary specification/data sheet? expected release date?

    If there is no NDA, we will be making the device available on TI.com by mid-august which is around one month from now. 

  • 0 in reply to Praveen GD
    Prodigy 40 points

    We should have one .... we are checking

  • 0 in reply to william Washington
    TI__Guru 57737 points

    Sure. Please let me know if we have an NDA.

  • 0 in reply to william Washington
    Prodigy 40 points

    While that information is being found, I have another question relating to the LM74800:
    On Friday I downloaded TINA-TI and the TINA-TI CS transient model for LM74800 - I loaded it into TINA and tried to run it but it contains several subcircuit models for other components (FETs, Diodes, Capacitors) which are not included, therefore It won't run in TINA-TI.....

    Are you able to help, please?

  • 0 in reply to william Washington
    TI__Guru 57737 points

    Hi William,

    You can replace the FETs, Diodes in the schematic with the ones available in TINA to resolve the issue.

    Else, you will have to import the Spice Library file for the components you like to simulate into TINA. You can refer to the training video below.

    Importing SPICE models into TINA-TI(TM) simulator

  • 0 in reply to Praveen GD
    Prodigy 40 points

    I could not find any suitable FETs in TINA-TI's library, so I downloaded Pspice for TI and the LM74800  CS model for Pspice, but get errors when I try to run it:
    --------------- INFO(ORPROBE-3209): Simulation Profile:  LM74800-Q1_CS_configuration-trans ---------------
    INFO(ORPROBE-3183): Simulation running...
    ** Profile: "LM74800-Q1_CS_configuration-trans"  [ C:\DATA Sheets\TI\slvmdb8\LM74800-Q1_PSPICE_TRANS\lm74800-q1_trans-pspicefiles\lm
    Reading and checking circuit
    ERROR(ORPSIM-16306): Must be a two terminal device
    Circuit has errors ... run aborted
    See output file for details
    INFO(ORPROBE-3188): Simulation aborted

    The error reported makes no sense to me, are you able to help please?

  • 0 in reply to william Washington
    TI__Guru 57737 points

    Hi William,

    Let me check and get back to you.

  • 0 in reply to Praveen GD
    Prodigy 40 points

    We are still waiting for our legal/admin people to get back with the NDA details....

  • 0 in reply to william Washington
    TI__Guru 57737 points

    Hi William,

    I have shared with you the unencrypted PSpice model of LM7480-Q1 in private chat.

  • 0 in reply to william Washington
    Prodigy 40 points

    Hi Praveen,
    Apologies that it has taken so long to get the NDA details.
    Please refer to NDA with Seeing Machines 2020-07-07-85343 effective 07/07/2020 including amendments dated 12 March 2021 and 24 September 2021.
    We are interested to the new device which you referred to earlier in this chat:
    "We do have a device which will be released in a couple of months which can work in CS topology and also has over current and short circuit protection."

    Are you able, please to share with us privately the new part number and preliminary data sheet?

    Best Regards
    Bill

  • 0 in reply to william Washington
    Prodigy 40 points

    To clarify, the NDA is between Seeing Machines and TI.

  • +1 in reply to william Washington
    TI__Guru 57737 points

    Hi William,

    Let us take this discussion on email.