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TMUX7462F: Automotive 1PPS & ADC (5V) input with short to battery (36V) protection

Vincent Chiu
Prodigy 190 points
Part Number: TMUX7462F
Other Parts Discussed in Thread: TMUX1308-Q1

Tool/software:

Hi TI Expert

I read the application note #scpa071 (Short to Battery Protection with TI Analog Switches and Multiplexers) and want to survey the input protection component for 1PPS and ADC input, all are 5V level, for automotive application. And PPS and ADC ports need to test with ISO 16750-2 short to battery test with 36V/60 sec.

Could TI expert recommend the feasible part, TMUC7462F is feasible solution?

 

Regards,

Vincent

  • 0
    TI__Mastermind 29648 points

    Hi Vincent,

    I'm not really familiar with the details of ISO 16750-2 but from a quick look up it looks like it doesn't exceed about 36V but I couldn't really find anything about the current.
    TMUX7462F should be able to support the voltage need (supports up to +/-60V but would you be able to provide what the max current needed here would be?

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 190 points

    Hi Rami

    The test is the input/output pins of vehicle ECU need to be protected/ not damaged when pins short to vehicle battery (our condition is 36V) or GND, the time duration is 60 sec.

    TI's document # scpa071 (Short to Battery Protection with TI Analog Switches and Multiplexers). Our current solution is same as declaration with "implementing external diode and resistor networks as shown in Figure 1-1 to keep the input signals within the supply voltage" in SCPA071. However, we found the power source of 5V may be damaged.

    TMUX1308-Q1/TMUX 1309-Q1 may be the feasible solution for us, but we need 4 channel 1:1 multiplexier (same as TMUX7462F). Does TI has recommend parts?

    Thanks

    Vincent  

  • 0 in reply to Vincent Chiu
    Prodigy 190 points

    Hi Rami

    TUX1308-Q1 or TUX1309-Q1 not meet our requirement is because the absolute maximum rating of Vs is only 6V with VDD=5V condition.

    Please help us to check if TMUX7462F the input IO could be shorting to the battery voltage, VBAT (36V) and without damaged?

    Regards,

    Vincent

  • 0 in reply to Vincent Chiu
    TI__Mastermind 29648 points

    Hi Vincent,

    For the 1308/1309-Q1 the Vbat level can be above the abs max. It's specifically highlighted in the datasheet in section 10-2
    But an Rlim will be required. 
    For example here's the table for 12.5mA through the switch. 


    We won't have a 1:1 version though so 1309-Q1 would be the best option.

    If we wanted to go with TMUX7462F, it could also work we just don't have testing done on it for that specific event. But really it will just go Hi-Z when they go above the supply + threshold.

    A few things that may make it not work would be the supply voltage, threshold, and the response time.
    The low end supply voltage for single sided is 8V so they would need atleast an 8V rail or they could do +/-5V. Of course this depends on the regular voltage they would be using in normal operating conditions. But given that the fault will only trigger at VDD + threshold. So they would need to make sure that the downstream devices can handle the operating voltage + the 0.7V (typ) threshold. They may also want to add some limiting resistor on the input just for extra safety in theory it shouldn't be required since the device will fault above the supply and the current should be limited.
    Should be aware as well 500ns for the response time. 

    Thanks,
    Rami