• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 1525 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

THS4551: Quiescent current v/s Actual operating current

DEEPAK V14
Intellectual 810 points
Part Number: THS4551
Other Parts Discussed in Thread: ADS8900B, TINA-TI

Hi,

The Quiescent operating current of THS4551 is listed as the maximum of 1.92mA in the datasheet. The supply pins VS+ is connected to 5Volt and VS- is grounded.
Fully Differential Amplifier THS4551 is used to implement a Band Pass Filter with pass band range in between 20Hz and 285 kHz with an amplification factor of 10.
The output of THS4551 (OUT- and OUT+) is connected to the analog input (AINP and AINM) of ADS8900B through a charge kickback filter.

Q1. How much additional supply current other than Quiescent operating current (1.92mA) have to be provided by 5Volt supply rail to VS+ for proper operation of the design?

Q2. Do the supply current requirement of THS4551 increases with gain it provides to input signal?

Q3. Do the analog inputs (AINP and AINM) of ADS8900B have high input impedance? How much current will flow to this inputs from outputs (OUT- and OUT+) of THS4551? 

Thanks in advance
DEEPAK V

  • 0
    TI__Expert 8720 points

    Hi Deepak,

    The amount of additional current you will need depends primarily on the voltage level you are trying to drive from the outputs of the amplifier. The maximum voltage swing divided by the total effective load (combination of feedback networks, load resistors, load capacitors, and ADC inputs) will give you the peak amount of current the amplifier will consume. The easiest way to estimate this is to run a quick TINA-TI simulation using the THS4551 model in an equivalent circuit to the application.

    If you know the peak output voltage, I can help you run a simulation to determine the dynamic current consumption.

    Regards,

    Jacob

  • 0 in reply to Jacob Freet
    Intellectual 810 points
    Hi Jacob,

    Thank you for extending your grateful support. The peak output voltage will be around 3.8Volt.

    Thanks and regards
    DEEPAK V
  • 0 in reply to DEEPAK V14
    TI__Expert 8720 points

    I ran a simulation using TINA-TI and your circuit at 3.8Vpp output and measured approximately 11.2 mA peak from the supply current as shown in the graph below. You can download my schematic from this link TINA Simulation. For you power supply, you will of course want to design for some extra current beyond what the simulation shows to account for any unpredicted current requirements.

  • 0 in reply to Jacob Freet
    Intellectual 810 points

    Hi Jacob,

    I have simulated the TINA design file uploaded by yourself and found that the supply current requirement is around 11.2mA.
    I will also take care for the extra current margin to be kept while finalizing the power supply requirement. 

    Thanks once again for helping to solve my doubts.

    Thanks and regards
    DEEPAK V