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# THS4511-SP Power consumption

On page 5 of the data sheet for the THS4511-SP it lists the max and min Quiescent Current. Is the Quiescent current draw the only current draw through the THS4511-SP? Is it correct to assuem this is a constant current device where the current only varies with temp and supply voltage?

Thanks

• Stephen,

The quiescent current of the device is the current that the device will draw when there is no load connected to the device and the inputs are biased to mid-rail (or left floating, in the case of this op-amp).

Depending on the input/output networks and the overall load of the device the current consumption of the op amp will change.

• Hi Jeffrey,

Thanks for the reply. I have a follow up question for you- is there an app note on how to calculate the total current draw of the THS4511-SP when configured to drive an ADC as shown in figure 44 (or figure 43) of the THS4511-SP data sheet?

• Stephen,

I don't believe we have any app notes specifically addressing this issue, however maximum current can be easily calculated using ohms law: V=I*R.

Your total current draw from the amplifier will be equal to the quiescent current of the device plus the input current (negligible given the input impedance) plus the output current.

Output current is merely going to be a function of the impedance of the load of the device.  Calculate the total impedance at the output of each terminal and determine what your maximum voltage swing will be and you can get the maximum output current of Io=Vmax/R.

If you'd like to simulate it, you could use TINA-TI (http://www.ti.com/tool/tina-ti) to check the current through the supply lines using an ammeter.  Just setup the configuration you'll be using and it'll give you a good idea of what the current should look like on the bench.

• I went ahead and drew up a quick schematic as a basis for you to test your circuit.  I took the input impedance from the ADS5500 and put it in a block, then set the circuit up identical to figure 43 in the THS4511 datasheet.

According to DC analysis, you get 38.04mA of DC current into the amp when driven with the signal I used.  Feel free to adjust the circuit as necessary to simulate your own design.

http://e2e.ti.com/cfs-file.ashx/__key/communityserver-discussions-components-files/10/8372.THS4511_2D00_Example.TSC