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ISO7721-Q1: What do you mean supply current - DC signal and AC signal?

Yoshiki Ochi
Expert 7885 points
Part Number: ISO7721-Q1

Hi team, 

Could you answer lower questions 1~3 for supply current ICC1 and ICC2 shown in lower list?
I referred to "6.10 Supply Current Characteristics—5-V Supply" in datasheet of ISO7721-Q1.

For "Supply current - DC signal, VI = VCCI (ISO7721-Q1 with F suffix)"...

  1. Is the secondary side consumption current (ICC2) 2.2Atyp in the case primary side signal keeps high?
  2. Is each of primary and secondary side supply current 2.2Atyp which means total 4.4Atyp consumption current in the case primary side signal keeps high?

For "Supply current - AC signal, All channels switching with square wave clock input; CL = 15 pF"...

3.  Does datasheet say that secondary side consumption current ICC2 is depending on primary side signal frequency, and vise versa?

If there are no correct understanding in upper list, could you tell me correct one?

Regards,
Ochi

  • 0
    TI__Genius 17100 points

    Hi Yoshiki-san,

    Your understanding for these datasheet values is largely correct. The main discrepancy I believe comes from confusing the "primary side" of the isolator with an isolated channel's "inputs."

    By "VI = VCCI", the datasheet is specifying the input condition for each channel, so for your question (1.), the current consumption for both Icc1 and Icc2 will be 2.2mA typ on each side of the isolator because the ISO7721F-Q1 has one forward channel and one reverse -- if both inputs are in the HIGH state (VI = VCCI), the same amount of current will be consumed by each side of the isolator.

    For (2.), the total current consumed by the isolator is 4.4mA typical (2.2mA on each side), and this will be true so long as both input signals of the isolator are HIGH for ISO7721F or LOW for ISO7721-nonF.

    For (3.), current consumption of each side of the isolator will change based on the behavior of the channels. If the input channel is switching, the output of the isolator will have to output the same switching signal, consuming more current. Therefore, the current consumed by the primary side (Icc1) is dependent on the behavior of the side 2 input (channel A) while the current consumed by the secondary side (Icc2) is dependent on the signal input on side 1 (channel B).

    Please let me know if there is additional clarification I may provide.


    Thank you,
    Manuel Chavez