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ADuM1200 drive MMBF170L mosfet


My original designing use 5V optocoupler to finish the isolation function, optocoupler output drive the MMBF170L mosfet at ON or OFF state with very low frequency.

Now, I feeling ADuM1200 chip also can finish the same function, the better thing is this way need less current than optocoupler.

Due to I never use ADuM1200 chip to drive the MOSFET, I have a little bit worry about whether it can work well.

Could you helps to take a look it, whether it is a normal usage without risk.


  • Hi, this is my original circuit, use optocoupler to drive the MMBF170L MOSFET, now, I want to replace the optocoupler with ADuM1200 chip.

  • Hi,

    how fast do you want to turn on/off Q6?

    ADuM1200's output impedance is around 60-70 ohm. 

    if 10K ohm is exactly value for R113 in your application, ADuM1200 can turn on Q6 well.


  • Hi, Very thanks for your helps.

    Could you kindly helps to take a look my modified circuit again.

    The Q6 on/off frequenty is very very low, most of time, Q6 keep ON or OFF state without no change, only in some time, Q6 need change state once.

    My analysis is ADUM1200 chip can drive mosfet work well, just due to I never used it before, so, have a littlt bit worry about it, it is very helpful if you can helps to affirm this.


  • You might also consider the ADuM1240/45 since the switching frequency is low. These micropower isolators have longer prop delay and a more restricted power supply range, but static power dissipation can be as low as a few µA. The ADuM1240 has a default high output state when the input supply is disabled, while the ADuM1245 is default low.

  • Hi Weidong:

    The schematic is OK. Only one suggestion to place R84 directly between G, S of Q8. 

    As Dave has suggested, please pay attention to the fai-safe logic status when choosing digital isolator.  it appears during the period of VDD1 and VDD2 to ramp up.

    please go to below link to search for the right part:


  • Hi, Chris,

    I feeling our i-coupler device have some good feature compare with opto-coupler.

    Also, there are 2 items make me confuse, could you share some your thought with me.

    1. I saw that we also have 1 channel i-coupler device, such as: ADuM1100, but the price almost same with 2 channels chip, compare with 1 channel opto-coupler, the 1 channel i-coupler almost have twice price, could you let me know the reason of this, whether the price of 1 channel opto-coupler will become cheaper someday. Or, could you helps to take a look which i-coupler chip can replace HCPL-0600 opto-coupler with lower price complace with ADUM1200. We use ADUM1200 chip at several module, so, I use this chip to replace the opto-coupler now.

    2. You know CMOS device have "Input transition rise or fall rate" requirement, such as: 20ns/V, we must control the input rise or fall rate fast than this data, whether i-coupler device also have this requirement.


  • Hi Weidong:

    material is only one factor of price, there are also others such as market size, volume......

    besides ADuM1200, ADuM724x and ADuM120/1N could also be considered. 

    there is schmitt trigger circuit designed in side the input port, so there is no transition rate limit.



  • Also Weidong, the ADuM1100/1200 are older generation products. The latest generation is ADuM110N (1-ch) and ADuM120N (2-ch). They are more cost-effective and have better performance and robustness.

  • Hi, Dave,

    Very thanks for you kindly reply.

    And, I am confusing one item.

    Here is my circuit, replace opto-coupler with our ADuM1200 chip. Isolate LOGIC side(VDD1 side) and FIELD side(VDD2 side).

    The result I needed is:

    The Q9 on/off frequenty is very low, most of time, Q9 keep ON or OFF state without no change, only in some time, Q9 need change state once, but,

    When logic side input 1, field side need output 1.

    When logic side input 0, field side need output 0.

    When VDD1 or VDD2 failed, output need keep 0.

    Then, I found use ADuM1200 is incorrect, because when VDD1 failed, output keep 1.

    Then, I found use ADuM1210 can solve this, when VDD1 failed, output keep 0.

    But, Please take a look the under Truth Tables.

    If VDD2 failed, output state is "Indeterminate", I can't understand the meaning of it, is it possbile outout is 1 or 0? If so, looks I can't use this chip, due to I need keep outout to 0, 1 will generate very bad result.

    Could you helps to analysis whether my understand is correct.

    And whether we have one chip can fit my requirement.

    Or, whether it is not a good usage I use this chip on here, you know i want to replace opto-coupler with i-coupler.

  • Hi Weidong:

    When VDD2 is below UVLO point, the output is high impedance. By adding 10kohm pull down resistor, we can get a logic L output.


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