• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 14 subscribers
  • Views 2275 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Component for driver input isolation

Julien Djn
Intellectual 840 points
Other Parts Discussed in Thread: ISO7841, SN6501

Hello,

We are developping a solenoid driver that will be mainly used in automotive applications.

In our driver, we will receive the command signals directly from the car controler (wire signal tied to GND or open). Frequencies can reach up to 1-2kHz.

I look for a component to isolate these signals, to avoid any perturbation and false detection.

Plus, this component has to be very small for an easy integration in our electronic.

I already know the ISO7320 and ISO7841, that I used before on PWM application (for electric motor control). Can I use the same isolator ?

Or would you recommand to use other isolator ? Shall I add Schmitt-trigger on all my inputs ?

Thank you,

Best regards,

Julien

  • 0
    TI__Guru 62480 points
    Julien ,

    Moving to industrial interface forum for support.
  • 0 in reply to ShreyasRao
    TI__Guru 55815 points
    Hi Julien,

    Based on the isolation rating required, you could use ISO73xx (basic) or ISO78xx (reinforced) both of them should work fine. If the car controller output is CMOS or is compatible to ISO7xxx inputs, you could use it directly. If the car controller output isn't compatible you may need a compatible Schmitt to get CMOS logic levels.

    If you do not have isolated power on the other side and need to generate isolates power for ISO7xxx, you can use SN6501 / SN6505 to do the same.

    Regards,
    Koteshwar Rao
  • 0 in reply to Koteshwar Rao
    Intellectual 840 points

    Hello Rao,

    Thank you for your answer.

    One question : how can I check if the car controller has a CMOS output ? For the moment all that I know is : injection ON when signal is tied to GND ; injection OFF when signal floating. I will try to get the exact schematics.

    Would you have any application note that talks about compatibility between controller outputs and isolator (or other kind of devices) inputs ?

    Best regards,

    Julien

  • 0 in reply to Julien Djn
    TI__Guru 55815 points

    Hello Julien,

    I am attaching a snapshot of ISO78xx datasheet that lists input logic level requirements of the device ISO78xx. Based on VCCI applied, min Input High Voltage (VIH) should be at least 0.7*VCCI & should not exceed VCCI. Max Input Low Voltage should be at most 0.3*VCCI & shouldn't go below 0V.

    In your case, car controller output is either floating or GND hence you could use a pull-up resistor of 4.7kΩ from car controlling output pin to VCCI (2.25V to 5.5V) which will make the pin be either HIGH or LOW. This should be a valid input for ISO78xx family of devices.

    There will be similar requirement for ISO73xx family that should be mentioned in the datasheet.

    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Intellectual 840 points
    Great, thank you !

    Best regards,
    Julien
  • 0 in reply to Koteshwar Rao
    Intellectual 840 points

    Hi,

    I would have another question : how can I protect the isolator against the 12V voltage (as in a vehicle, a 12V signal could possibly be wired on the isolator input by mistake), or short-circuit 5V to ground ?

    Best regards,

    Julien

  • 0 in reply to Julien Djn
    TI__Guru 55815 points

    Julien,

    Since digital isolators are generally used to interface two or more digital blocks (like MCU, ADC, etc.) the I/O voltage levels are well regulated. In your application, if inputs are expected to go beyond acceptable voltage levels you might be required to add external circuitry for protection. Few of the examples for protections include using TVS / Zener diode for voltage clamping / limiting and current limiters for short circuit protection.

    Regards,
    Koteshwar Rao