• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 46 subscribers
  • Views 444 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.

ADS7038-Q1: AINx, AVDD and DVDD maximum current consumption by the pin

Vishwas H R
Prodigy 240 points
Part Number: ADS7038-Q1

Hello,

I have few queries related to current consumption of the pins.

1. What is the maximum current consumption of AINx pin when used as analog input?

2. What is the leakage currentof AINx pin when used as analog input (I can see it is mentioned only GPIO input)?

3. What is the maximum current consumption of AVDD Pin? The reason for this question is AVDD should be much greater than current of the analog input or digital interface and I'm giving 3.3V supply.

4. What is the leakage current of AVDD Pin for 3.3V supply?

5. What is the maximum current consumption and leakage current of DVDD Pin for 3.3V supply?

6. What is the voltage across DECAP (internal power supply)?

  • +1
    TI__Mastermind 24358 points

    Vishwas,

    Below are answers to your question in red.

    1. What is the maximum current consumption of AINx pin when used as analog input?  The current input on the analog inputs is primarily due to the charging of the 12pF sample and hold capacitor.  Depending on the sample rate, and the input voltage change for each sample the current will be different.  The worst case can be calculated by using the charge equation Q=CV, and the current equation I = deltaQ/deltaT.  For a 1Msps sampling rate and a 5V change between samples the current is calculated as (12pF*5V/1us = 60uA).  The 5V change means that the input for the first conversion is 5V and the input for the next conversion is 0V.  In other words, alternating conversions will have worst case changes in input voltage.  In most applications this will not be the case and the actual input current will be lower.  

    2. What is the leakage current of AINx pin when used as analog input (I can see it is mentioned only GPIO input)?  The leakage for analog inputs is generally due to the input ESD structures, and is in the pico-Amps.  I believe in this case it is the same as with the GPIO.

    3. What is the maximum current consumption of AVDD Pin? The reason for this question is AVDD should be much greater than current of the analog input or digital interface and I'm giving 3.3V supply.  The current is specified in the table that you copied from the data sheet for 3.0V.  You can do do a linear projection to determine the current at 3.3V

    4. What is the leakage current of AVDD Pin for 3.3V supply?  The leakage current at 5V is specified as 25uA max.  The leakage at 3.3 will be somewhat less than that, but you can assume 25uA worst case.

    5. What is the maximum current consumption and leakage current of DVDD Pin for 3.3V supply?  The current on DVDD relates to the bus capacitance that the digital IO will drive.  Physically longer bus lines will have more capacitance and more current will be drawn from DVDD to drive them.  This video shows the calculation:  adcs-sar-adc-power-scaling.  Basically it uses the same calculation as given in step 1 above.

    6. What is the voltage across DECAP (internal power supply)?  I need to check on this.  I will get back with you.

    Art

  • 0 in reply to Art Kay
    Prodigy 240 points

    Sure, thanks a lot.

    let me know once you get information on voltage across DECAP (internal power supply).

  • 0 in reply to Vishwas H R
    TI__Mastermind 24358 points

    Vishwas,

    The DECAP voltage is 1.76V.  

    Best regards,

    Art

  • 0 in reply to Art Kay
    Prodigy 240 points

    Thanks,

    Can i know what would be the leakage current for DVDD Pin?

    Also, what would be pin capacitance across all the input and power pins?

  • 0 in reply to Vishwas H R
    TI__Mastermind 24358 points

    The DVDD static current is in the nano-amp range.  This is the current with no digital communications.  When converting, the current will be higher and will depend on the bus capacitance.  I measured about 10uA on the EVM when converting at the default sampling rate.  See adc-power-scaling-video for details on estimating dynamic DVDD current based on your bus capacitance.

    Best regards, Art

  • 0 in reply to Art Kay
    Prodigy 240 points

    Can i know pin capacitance of DVDD pin as well as analog input pin to use for the calculations mentioned in adc-power-scaling-video

  • 0 in reply to Vishwas H R
    TI__Mastermind 24358 points

    Vishwas,

    The pin capacitance needed to calculate I(DVDD) is not the pin capacitance of the DVDD pin.  Rather it is the capacitance of DOUT.  The reason is that the DOUT pin driving the trace and microcontroller is what consumes power.  This power is taken from the DVDD supply.  The pin capacitance of the DOUT pin is less than 1pF.  This is based on the IBIS model of similar devices.  You will also need to include the microcontroller pin capacitance and trace pin capacitation in your calculation.  You can likely estimate most microcontroller capacitances to be 2pF.  So, you just need to find your trace capacitance to calculate the current.

    Art