Using multiple RS232 isolation channels

Hi,

We were considering the use of ADM3251E for multiple channel RS232 isolation, in which we may use upto 9 chips (A future products may use 17 channels). But I find that use of 9 x ADM3251E would need more than 1A supply current which is not acceptable. I am also worried about the EMI issue if there are so many isolation chips on a single PCB. Can you suggest a way to achieve this by using lesser current? The overall cost of the solution should not exceed the cost of the ADM3251E based solution. I was considering ADM3252E which appears to be more efficient, but I found the cost to be on the higher side at $ 8.49 compared to $ 2.99 for ADM3251 even if I were to use the ADM3252 for 2 channels.  Please suggest a way out. Also please let me know the EMI related precautions that we may have to take in handling so many isolated channels.

Regards,

Hemant

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  • Hi Paul,

    Thank you for the response. Since our usage demands only low speed transmit/receive and ground for isolated RS232 port, I thought of using a combination of ADUM5201 for power and isolation, and ADM101E(or equivalent) for level conversion. This may be equivalent to ADM3251E, but will need much less current on the primary side, which should not exceed 25-30 mA even when RS232 is loaded. The cost of two chips could be higher than that of ADM3251E, but the benefit of saving close to 700mA current while using 9 channels will bring other benefits too. If I need more control signals, I will think of adding ADUM141X devices and low power RS232 level converters such as ADM3315E while deriving isolated power for them from the ADUM5201. What do you think?

    Do you also think a separate ESD surge suppressor diodes be used at the ADM101E's RS232 pins?

    Regards,

    Hemant

Reply
  • Hi Paul,

    Thank you for the response. Since our usage demands only low speed transmit/receive and ground for isolated RS232 port, I thought of using a combination of ADUM5201 for power and isolation, and ADM101E(or equivalent) for level conversion. This may be equivalent to ADM3251E, but will need much less current on the primary side, which should not exceed 25-30 mA even when RS232 is loaded. The cost of two chips could be higher than that of ADM3251E, but the benefit of saving close to 700mA current while using 9 channels will bring other benefits too. If I need more control signals, I will think of adding ADUM141X devices and low power RS232 level converters such as ADM3315E while deriving isolated power for them from the ADUM5201. What do you think?

    Do you also think a separate ESD surge suppressor diodes be used at the ADM101E's RS232 pins?

    Regards,

    Hemant

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