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Questions for LTC6811-1, LTC6812-1

Category: Hardware
Product Number: LTC6811-1, LTC6812-1

Hi. I have some questions regarding LTC6811-1 and 6812-1.

I'd like to know maximum power capacity of zener diode as below.

Please check if the capacities of LTC6811 and LTC6812 are different.

In isoSPI communication line using coupling capacitor, the recommended circuit on the datasheet has been changed as follows.

<before the change>

<after the change>

Applying the circuit after the change measures high radiation noise; applying the circuit before the change causes the signal level to be too low.

Please review if there is any problem in applying the damping resistance to 330 ohms and the termination resistance to 100 ohms. (Coupling C is 1nF, )

We will apply 1.4k and 601 ohms to Ibias side resistance. Do you have any other recommendations?

Additionally, if the Termination resistance is applied to the circuit at 100 ohms x2, please check if a 3.3V Zener diode is required (in the circuit before the change).

The transient voltage does not appear to exceed the maximum voltage range of the pin. I'm curious about the role of the Zener diode.

Thank you.

  • Hi,

    I moved this to the Battery Management System community. Someone here should be able to help.

  • Hello,

    The 590Ω resistor creates a resistor divider with the termination resistors and attenuates common mode noise and 590Ω value is chosen to provide the most noise attenuation while maintaining sufficient differential signal.

    and  Zener diodes are used at each IC for robust mechanism to bring the end potentials into a safe working area like clamp the common mode voltage to stay within the receiver’s input range.

    the receiver slicing should be set to ±300mV by selection of the isoSPI biasing control resistors RB1= 1.4kand RB2= 601Ω, for more information you can refer "Selecting Bias Resistors" section in datasheet.

    for maximum power capacity of zener diode - we will look into this and get back to you soon.

  • Hello,

    Would you share your answer about "for maximum power capacity of zener diode - we will look into this and get back to you soon."?

    My customer still need your answers.




    Jay shin is moved to other company.

    So I still need your answer for our customers.

  • May I know why do you want to know the power capacity of Zener diode? As per datasheet it is mentioned that when IC is operational the Absolute maximum rating of isoSPI pins (IP and IM pins) are in between 0V to VREG+0.3V, <6V. So we actually don't need the external zener diodes when they are on the same PCB. For external isoSPI coupling we use a transformer instead for which again the external zener is not required. 

    For capacitor coupling, the recommended circuit that you are showing is only for same PCB isoSPI coupling? Are you going to do that? If yes they you can go ahead with what is shown in datasheet. For multi PCB application please use the transformer coupling instead.  

  • Dear Abhishek,

    Thank you for your kind answer.

    But additionaly my customer asks that they want to know the maximum power specification of Zennor diodes in LTC6812-1 and LTC6811-1.

    (Its zennor diodes are located inside of LTC6812-1 and LTC6811-1 and Cx pins.

    And it measns zenor diodes in Fig.34 which is attached avove question.)

    Would you let me know maximum power specification of these zennor diodes?



  • Again, may I know why exactly you want to know the max power of the Zener diode? Please help me with your problem statement so that I can help you better. 

    Usually this information is not made public and we generally recommend everyone to refer to Absolute maximum ratings for any kind of threshold they want to know per pin.