ADG1609 Multiplexer Input Design

Hi,

I am using ADG1609 MUX and AD623 and AD7685 ADC

My source is low input impedance(100 ohm) differential accelerometer.

I have few doubts about the Multiplexer and its inputs:

1.I think ADG1609 does not have internal protection diodes hence I am connecting SD101 low leakage diodes externally.Is it having internal diodes?

2.It looks like on the digital side we don't need a level converter.I am powering the MUX by 10V and still I suppose it will read my uC signal's at 3.3V,Is this assumption correct?

3.I am combining my RFI filter with Antialaising Filter(128 Hz BW),pls find attached Schematic,Is this correct will it perform both the operations?

4.I think for ESD protection I need to put the ESD diodes of high current ability and high leakage at the front end only,otherwise the leakage current will flow through the input resistance and add a offset,do you think the ESD protection diodes are properly placed?Can't we use only SD101?

5.Is there any Circuit from the LAB or Eval board with MUX and its inputs protected as well as antilaising filter added and ESD protection?

MUXInputProtection.pdf
  • 0
    •  Analog Employees 
    on Jul 11, 2011 9:39 PM

    Hi ChaitanyaB,

     

    Please find the answers to your questions listed below:

    1. The ADG1609 is manufactured on a CMOS process and it uses internal ESD protection diodes on each of its pins.

       The ESD ratings achieved are as follows:

     

    • Human Body Model ESD: +/-1500V for both the TSSOP and LFCSP package options.
    • Field Induced Charge Device Model ESD: +/-1000V for the TSSOP package option and +/-1500V for the LFCSP package option.
    • Machine Model ESD: +/-25V for both the TSSOP and LFCSP package options.

     

     

    2.  With single 10V supply you can use the VIL and VIH specifications from the data sheet which allows direct connection to standard 3.3V digital signals without the need of level translation.

     

    3. This depends on the frequency response of each of the two filters. I would recommend testing the frequency response of the combined filters to confirm it performs the desired function.

     

    4. What is the level of ESD protection you need for your circuit?

    Assuming one of the channels of the multiplexor will always be on and since its ON resistance is low, it doesn't matter where the ESD protection diode is placed. Its leakage current will still produce offsets across the high impedances from the circuit. From a protection point of view however, it is recommended to place the diodes as close as possible to the point where the ESD discharge is expected to occur.

     

    5. At the moment we don't have any circuit from the lab or evaluation board that implements the protection of multiplexor inputs as well as signal filtering.

     

    Regards,

    FEB