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XTR117 Update Rate

Adam Hoover
Expert 5275 points
Other Parts Discussed in Thread: XTR117, XTR111, ISO1541, DAC7571, DAC7311

Hi,

 

Customer is going with the XTR117 (2 wire solution) (over the XTR111) and is looking at doing the PWM option like they are showing on page 7 of this datasheet.

In the end they would like to meet or exceed the 12 bit resolution they have today using a DAC and the update rate needs to be 3KHz min. 

“I would also like to use the Vreg output as the supply for the isolation... 

The trouble I'm having is again at that update rate (3KHz) and ~12 bit resolution on the PWM I need a ~100MHz isolator which requires more current then what can be supplied from the XTR 

Does TI have any recommendations for the XTR117 for 3KHz update, small, cheap and uses the Vreg output to power isolation?”

 

Customer looking at the ISO1541 for isolation.

 

Any suggestions would be appreciated!

Thanks,
Adam Hoover

ACAT Support

  • 0
    TI__Guru 64165 points

    Hi Adam,

    Unfortunately if they want to pass a 100MHz PWM signal over the isolation barrier then it's going to require more than 4mA of supply current which is more than a two-wire loop can support without using more circuitry.  Basically the two-wire system circuitry can't draw more 4 mA of current if the system is required to output the standard 4mA low-level for the 4-20 mA loops.  

    Achieving 3kHz update rate with a DAC is likely easier to implement because the SPI / I2C signals are not continuously transmitted like a PWM waveform.  Check out the DAC7571 (I2C 140uA at 5V) or the DAC7311 (SPI 80uA at 5V) and then the ISO74xx or 76xx devices.

    You can search the forum for a few other posts I've made regarding using the ISO products with the XTR devices, here's one:

    http://e2e.ti.com/support/amplifiers/precision_amplifiers/f/14/p/258994/911219.aspx#911219