• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 526 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.

ADS124S06: GPIOX pin leakage current ?

Mark Betts
Prodigy 70 points

Part Number: ADS124S06
Other Parts Discussed in Thread: ADS124S08

For the ADC ADS124S06, the GPIO pins (GPIO0-GPIO3) are connected to the Input multiplexer block.

The specification states the leakage current for the analog pins AIN0-AIN5 at <2nA (Temp Ambient = –50°C to +125°C)

I am looking to connect the GPIOX pins to the AINX for connected input sensor health checks.

What is the off state leakage current for the GPIOX pins, is it a similar level to the AINX on state leakage pin at <2nA as it is connected to the input multiplexer and the device is a reduced feature variant of the ADS124S08 ?

Are there any figures for the "off" state leakage current of the AINX and GPIOX the data sheet only lists the "on" state leakage currents ?

  • 0
    TI__Guru** 113765 points
    Hi Mark,

    Welcome to the E2E forum! The GPIO pins on the ADS124S06 are analog pins. However, where the analog pins differ in configuration internally between strictly an analog input and a GPIO configuration is with respect to logic state. When configured as a GPIO input, you would not want to leave the input floating as excessive current could be drawn. This would be a condition where both the PMOS and NMOS transistor are in an ON state.

    This differs from leakage. Leakage refers to current that would leak due to ESD or internal switches with respect to input connections. A floating input would have no source input but could draw mAs of current.

    So the GPIO pins are looking at logic state conditions and if your sensors are not at logic levels, then you will have an issue. So if you want to monitor voltages not specific to logic levels, I would suggest using the ADS124S08. The ADS124S08 will allow the same GPIO pins on the ADS124S06 to be configured as either GPIO or Analog input pins.

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 70 points

    Hi Bob,

    Yes I understand the P/N-MOS issue, but the GPIO inputs are stated as "GPIO pins use Schmitt triggered inputs" - Data sheet Figure 80 - Page 55 Doc SBAS660C-Aug 2016.

    The Schmitt input gate must be on the I/O input pad otherwise it would not work. A Schmitt digital input will not suffer from shoot through current, as soon as the threshold is reached the threshold shifts to a different level ?

    If they are configured as digital outputs to disturb the connected sensor to measure it's impedance, then configured as inputs it looks OK.

    Is the leakage current of the digital GPIOX a similar level to the AINX - as they are connected to the MUX block ?

    Regards,

    Mark.

  • 0 in reply to Mark Betts
    TI__Guru** 113765 points
    Hi Mark,

    Perhaps I did not make myself totally clear on the points I was trying to make. You are correct regarding the shoot-through current as I overlooked the Schmitt input for the GPIO. However, as I stated previously this would not be considered leakage anyway. My overall concern is how you intend to make a sensor diagnostic. Initially I was thinking that you were using the GPIO as an input for your sensor check, but now it appears as though you are intending to drive the sensor as an output for the diagnostic. Is my understanding correct?

    To help you try to understand the differences in the ADS124S08 and the ADS124S06, take a look at Figure 49 on page 32 of the datasheet. The dotted section marked 'ADS124S08 Only' is essentially the same as the ADS124S06 except the switches shown will always be in the open position. The switches shown in Figure 80 on page 55 of the datasheet apply to both devices as well.

    For the ADS124S06, the configuration is the same as the ADS124S08 device except that mux switches in Figure 49 cannot be closed. This means that with the GPIO switches shown in Figure 80 in the open state will have the same leakage current as the ADS124S08 device in the same configuration. However, once you close the GPIO switches there will be some additional leakage due to the added leakage path created by the output driver stage and the switch controlled by the GPIODAT register. We did not characterize that leakage, but we do have some simulation data which shows that the additional leakage is very small and almost negligible.

    So if your intention is to periodically drive your sensor using the GPIO as an output, then I would suggest that you use the GPIOCON register to open and close the GPIO switches as needed for minimal leakage (<2nA).

    Best regards,
    Bob B
  • 0 in reply to Bob Benjamin
    Prodigy 70 points
    Hi Bob,

    Yes the GPIO will be used to drive the sensor to measure it's impedance then switched to an input - so we don't want any I/O pin leakage current as this could degrade the input voltage reading.

    Yes we intend to periodically drive the GPIO as an output, and thankyou for the simulation data information and confirmation that it should be negligible leakage current as with the AINX pins.

    Thanks,

    Mark.