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ADS1258-EP: ADS1258-EP

William Rivera
Prodigy 10 points
Part Number: ADS1258-EP

Hi:

Page 25 has a paragraph that talks about not driving the analog/digital inputs prior to applying the supply voltages:

"The analog and digital supplies should be applied
before any analog or digital input is driven. The power
supplies may be sequenced in any order. The internal
master reset signal is generated from the analog
power supply (AVDD – AVSS), when the level
reaches approximately 3.2 V. The power-up master
reset signal is functionally the same as the Reset
Command and the RESET input pin."

We are using the ADS1258-EP ADC in one of our recent designs and would like to understand this some more.

Why is it is required that the supply voltages are applied first? We think is to avoid damaging the ESD diodes.

If that is not the reason, then why is it? and what is the potential damage that can occur?

In our design we are Is there a voltage range (or a current range) on the analog inputs that it can tolerate without no damage?

Thanks



 

  • 0
    TI__Mastermind 40211 points

    Hi William Rivera,

    You are correct, there are ESD diodes on each input that are connected to the supplies, similar to the configuration shown in the image below.

    When VIN > AVDD or < AVSS, one of these diodes will turn on. While this usually is not an issue when the supplies are present because it is easier to maintain AVSS < VIN < AVDD, when AVDD = AVSS = 0V i.e. the system is off, almost any voltage on the input pins will cause these diodes to turn on. This creates a low impedance path to ground, enabling potentially lots of current to flow into the pins and through the ESD diodes. It is possible that this set of conditions could cause permanent device damage.

    Therefore, you should at least try to limit the current drawn into the device to <10mA (as per the absolute maximum ratings table in the datasheet), the device will likely be okay. That being said, we cannot guarantee device performance if you violate the recommended operating conditions, nor can we guarantee device operation if you violate the absolute maximum ratings. I.e. you do so at your own risk

    My best advice would be to ensure that you are not applying signals to the device when the supplies are off.

    -Bryan