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ISO1176: ICC2

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Replies: 4

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Part Number: ISO1176

Dear Technical Support Team,

・ About ICC2 described in the ISO1176 datasheet (7.6 Supply Current)

> ICC2 5.25V DE at VCC1, 25 Mbps, 54-Ω load: 75mA

This value is
・ Current consumption on the 5V logic side of ISO1176
・ 5V terminating resistor connected on ISO1176

Is ICC2 = 75mA a value that includes both of the above?


Currently my thoughts are as follows
・ Current consumption on the 5V logic side of ISO1176: 75mA
・ 5V terminating resistor connected on ISO1176:  100mA  (5V/50Ω=100mA: 50Ω in parallel calculation because both two ISO1176 have 100Ω termination)

Total =  75mA + 100mA = 175mA

I my understanding is not correct, could you share correct calculation ?

Best Reards,

ttd

  • The supply current ICC is defined as the current that flows into VCC and out of GND. When the device is driving the RS-485 bus, then the current through the bus (and its termination resistors) also goes through these pins, so it is already included in the specified ICC.

    The voltage over the termination resistors is not 5 V but |VOD(SS)|. The difference between the specified ICC values for DE low and high is 55 mA, which would correspond to less than 3 V.

  • ttd,

    ICC2 is the current consumed by the ISO1176 on the bus side. The ICC2 values given in the datasheet to already account for the current flowing through the terminating resistor and therefore does not need to be added.

    Figure 2 of the datasheet shows ICC2 over a range of signaling rates for both 3.3V and 5V supply voltages.

    Respectfully,

    Lucas Schulte

  • Genius 5940 points

    In reply to Lucas Schulte9:

    Hi Lucas Schulte,

    Thank you for your reply

    Is total current  Icc1(logic side) + Icc2(Bus side)?

    So 11mA(Icc2: DE at VCC1, 25 Mbps ) + 75mA (DE at VCC1, 25 Mbps, 54-Ω load) = 86mA?

    figure 2 doen't  include 25Mbps and it's larger than 75mA, for example around 80mA at 10MSPS.

    What' the difference between them?

    Best Regards,

    ttd

  • In reply to ttd:

    ttd,

    Is total current  Icc1(logic side) + Icc2(Bus side)?

    -Yes

    What' the difference between them?

    -Figure 2 shows characteristics with no load vs the table of section 7.6 stating load conditions. I would use this table to more accurately gauge current consumption in application.

    Respectfully,

    Lucas Schulte