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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    •  Analog Employees 
    on May 21, 2012 12:45 PM

    Hi Hemant,

    The ADM101E works off a 5V supply and has a lower Txout output voltage swing so doesn't require the additional voltage doubler capacitors that you need on other RS232 parts. If you have a suitable 5V supply from the ADuM5201 and the output levels are sufficient (which they probably are as you mention you only require low speed transmit/receive) then the ADM101E is probably a good fit. The ADM101E also has 15kV ESD protection on the I/O pins so I don't think any extra protection will be required. Just ensure that you use low ESR capacitors for Vcc and V- pins (e.g. X5R, X7R series).

    Rgds,

    Paul

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  • 0
    •  Analog Employees 
    on May 21, 2012 12:45 PM

    Hi Hemant,

    The ADM101E works off a 5V supply and has a lower Txout output voltage swing so doesn't require the additional voltage doubler capacitors that you need on other RS232 parts. If you have a suitable 5V supply from the ADuM5201 and the output levels are sufficient (which they probably are as you mention you only require low speed transmit/receive) then the ADM101E is probably a good fit. The ADM101E also has 15kV ESD protection on the I/O pins so I don't think any extra protection will be required. Just ensure that you use low ESR capacitors for Vcc and V- pins (e.g. X5R, X7R series).

    Rgds,

    Paul

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