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ISO5451-Q1: About ISO5451-Q1 HW Design issue Consult

Liu Dong
Prodigy 190 points
Part Number: ISO5451-Q1
Other Parts Discussed in Thread: ISO5451

Hi All , 

I have used ISO5451 for HEV Motor driver project ,but I have some questions about the use of this chip,  for the PINs IN-、IN+,both has Internal pull-up resistor. whether it's not similar with Optocoupler, how to design to  finish the external hardware interlock function? 

  • 0
    TI__Intellectual 1665 points

    Hi Dong,

    The internal pull-up and pull-down resistance value is in the range of 40k-100k. The R of the input RC filter and the internal pull-down resistor form a voltage divider. The R needs to be small enough to make the voltage divider ratio close to 1 as possible. In your circuit, you have used 100Ohm. The interlock circuit should be effective.  

    With Regards,

    Xiong

  • 0 in reply to Xiong Li
    Prodigy 190 points
    Hi Xiong,

    I want to know when U1 IN-( pull-up resister by internal ) connect to U5 IN+(pull-down resister by internal) , and U1 IN+ connect to U5 IN- , how to determine the status . because IN- pull-up and pull down resistance now. I need to external design to solve this function.
  • 0 in reply to Liu Dong
    TI__Intellectual 1665 points

    Hi Dong,

    Normally, you would drive the IN+ and IN- to be either H or L. You don't need to do anything special if that is the case. Otherwise, you can add a pull-up resistor on IN- pin and pull-down resistor on IN+ pin. That way the voltage on the pins would be dependent on the voltage divider ratio of external pull-up/down resistor and internal pull-up/down resistors. With a reasonably small value of the pull-up/down resistors (eg 10k), the voltage on the IN+ pin can be L and H on the IN- pin. With this, the driver output will be in OFF state when the inputs are in HiZ.

    With Regards,

    Xiong