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XTR305：XTR305 power supply problem

Meng jeffrey
Expert 2760 points
Part Number: XTR305
Other Parts Discussed in Thread: LM317

I use 3 XTR305s in my design and output 0~5V or 4~20mA. The negative power supply of the XTR305 is designed to supply -9V. The TC7662 is used to provide -9V, and the output current of the TC7662 is 20mA.

Does the TC7662 meet the power supply for the three XTR305?

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  • 0
    TI__Guru 55466 points

    Hi Jeffrey,

    The maximum quiescent current of the XTR305 is 2.8mA; so the maximum quiescent current for 3 devices can be up to 8.4mA.  In addition, each XTR305 can support +/-20mA output current (linear up to 24mA).  If the XTR305 is only to be used on a standard 4-20mA application, where the XTR305 output is always configured to source +4mA to +20mA in the application, the output current in this case is supplied by the positive rail supply (LM317 linear regulator on your schematic); and the negative supply will only have to sink the total 8.4mA quiescent current.  However, if the XTR305 devices are expected to sink any negative output current in the application, the TC7662 negative supply will have to supply the total output negative current of all three XTR305 devices, in addition to the quiescent current; and the TC7662 may have issues supporting the total negative load current.

    The TC7662 is not a TI device, and does not specify the guaranteed output current supported, so I recommend to verify/check with the manufacturer for the guaranteed supported load current.

    Thank you, 

    Best Regards,

    Luis 

  • 0 in reply to Luis Chioye
    Expert 2760 points
    In the circuit design, XTR305 is used to output 4~20mA, or 0~5V. I use (+9V) to supply power to XTR305, and - 9V uses power IC with larger output current.

    The output voltage of XTR305 is 0-5V positive, so it is assumed that XTR305 can be supplied by a single positive power supply without using a negative power supply. Is it?
  • 0 in reply to Meng jeffrey
    TI__Guru 55466 points
    Hi Jeffrey,

    When using the device in Current Output Mode, the input voltage needs to be a minimum of (V-)+3V and a maximum of (V+)- 3V , in other words, the input signal has to be at least 3V away from the rail supplies. In addition, the minimum specified supply voltage range for the device to work to specification per the datasheet is +/-5V, as shown on Table 6.10 of the datasheet. Therefore, if the input voltage required in the application is 0 to +5V, you will require a negative supply of -5V and positive supply of +8V minimum.

    Best Regards,

    Luis