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disable adum1310 completely

Hi,

first my application is a galvanic isolated DAC with 4..20mA Ootput. I am using the adum1310 for the galvanic isolation of the Serial Interface of the loop powered AD421. I am using up to 6 of these couples parallel to transform digital data into my 4..20mA signal.

to reduce current consumption in battery-mode i thought i could switch of the VDDi using a mosfet driven by latch signal. the latch signal is also connected to the disable pin. unfortunately the adum1310 is consuming the quiescent current through the Clock, Latch and Data signalpaths.

is there any possibilty to reduce the current consumption without using logic elements to disconnect each signal?

regards

  • MBurke: As I see it, you need to reduce the current consumption of the ADuM1310 on the output side 2 to be much less than the 4mA minimum loop current.  The AD421 is specified for externally available current of 3.25mA, assuming 4mA flowing in the loop.  The quiescent current for the ADuM1310 in the lowest power mode with a datarate of DC to 2Mbps is specified for 1mA max IDD2 for VDD2 = 2.7V to 3.6V.  Is 1mA current too much? What is the current budget needed for the ADuM1310 from the loop?  Can you send a circuit diagram?

    If 1mA is too much, than an option is to use the 1 channel ADuM1100, which has a different architecture which reduces quiescent current a lot.  For VDD2 = 3.3V, the output supply current at a datarate of DC to 2Mbps is 0.04mA max for 1 channel, 0.12mA max for 3 channels. The ADuM1100 comes in SO-8 package, but 3 SO-8s are smaller than one wide body SO-16.

    Regards, Brian

  • Hello Brain,

    first thanks for your answer. The function of the isolator and the dac is not the problem...everything fine here. my problem is, that the primary side could be powered by battery or a power supply. In battery mode it could be necessary to power the whole device for a long period (4-6 month). in this case the 4..20 output isn't needed. but the serial interface still is in use by other components (microcontroller, adc, dataflash, etc.). so the consumption of about 6-7mA for all 6 isolators is a problem for me.

    like i mentioned a tryed to cut off the vddi of the adum1310 using a p-channel mosfet connected to the corresponding LATCH signal...but then it seems that the adum1310 draws the supply current over the serial interface pins from the microcontroller (each line has a 10k resistor in series). in my mind schmitttrigger inputs shouldn't draw more than some uA. my last solution would be the use of a logic circuit like 74hc241 to make the inputs tristate when not used. caused by the lack of pcb area this should really be the last option.

    as attachment one of the adum1310, ad421 couples...

    regards, Michael

  • Michael: The ADuM1310 inputs have ESD diodes that connect internally to VDD which provides a path to power up the ADuM1310 when the VDD pin is open externally from the MOSFET switch.  It may be best to add the external logic with tristate output to the ADuM1310 inputs to prevent the inputs from powering the ADuM1310.

    Regards, Brian