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  • TI Thinks Resolved

MUX508: reduce voltage drop when toggling EN pin

Part Number: MUX508

Hi all

Would you mind if we ask MUX508?
Could you refer to the attachment file and give us the advice?
1452.20180206_MUX508.pdf

Kind regards,

Hirotaka Matsumoto

  • Hi Hirotaka,

    Let me re-capture your question in the attachment. 

    <Measurement condtion>

    ・Power source:±15V(±5%)

    ・D-pin:0V ・A0, A1, A2, EN:High Level:5V, Low Level:0V

    <Question>

    When Multiplexer enables, at S1 output, it occurs 6.4V drops. Actual circuit, RC circuit includes. So, in case of actual circuit, S1 output connects to S/H circuit via RC filter. The voltage drop of actual circuit is 30mV(with RC circuit), however our customer would like to reduce it within 10mV. When our customer used MPC508, there is no voltage drop. So, our customer would like to use MUX508 with no drop.

    As our customer’s request,

    -they want to distribute 1ch DAC voltage to S/H circuit using MUX508

    -they don’t want to use huge value capacitance at RC circuit, because it will be delay of signal.

    If you have some advice, could you give us?(Especially, by removing the charge, we guess that it is possible to reduce drop voltage.)

    Fan Wang

  • Hi Hirotaka,

    I do not understand why the voltage drop can go to -6.4V. -6.4V does not seem to be charge injection effect only.

    If you believe charge injection is the root cause, here is the experiment I would do. Currently, their S/H is RC topology where R = 470 Ohms, C = 10 nF. Reducing R and increasing C while keeping RC time constant can help, for example, R = 313 Ohms and C = 15nF. It will not jeopardize the signal path's bandwidth.

    Or, C-R-C  Π topology can greatly help if your cutomer is open to PCB change.

    Fan Wang

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