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ADS7841-Q1: Maximum input current

na na78
Guru 16770 points
Part Number: ADS7841-Q1

Hi

According to the datasheet, ADS7841-Q1 seems to have clump diode to VCC at input channel (CH0-CH3) because its Vin (analog in) is restricted by VCC+0.3V as absolute maximum ratings.

So, the analog Vin(max) must be limited by 5.3V if VCC=5V.

In the customer’s system, we have to consider a situation that 18V may be applied to the analog input channel.

(It is for just in case that it might be happen accidentally, not in normal operation.)

Along with that, we want to offer the way to avoid device damage.

Please see the following image.

(A) We think using series resistor (20kohm in this case) could limit the current that conducts the diode in ADS7841-Q1.

(B) If clump diode is present between input and VCC, we think the voltage at CHx would be 5.3V.  It is not over absolute maximum ratings.

Then we have questions.

1.

Is our understanding (image diagram) correct?

2.

If our understanding is correct, we think we have to limit input current not to damage ADS7841-Q1.

How much input current  can be accepted by ADS7841-Q1 without any damage?

BestRegards

  • 0
    TI__Expert 5485 points

    Na Na 78

    Please see my reply below

    1. Using input series protection resistor to meet over voltage condition is one of the ways to protect ADC inputs1. OVP protection scheme shown above is correct.

    2. We do not have ESD diode DC current information. Typically most of the parts have ESD diode maximum DC current rating of 10mA. During over voltage condition It is recommended not to exceed current through these ESD diodes more than 1mA to keep internal power dissipation low. Vlaue selected by you (20k) looks ok as it will limit current to around 635uA.

     

    One of the better ways of doing this is to use external schottky diode (with forward drop 200mV) to clamp input to VDD in over voltage condition. This is especially required if 18V over voltage condition is a continuous event for ADC input.  

    You can also refer to one of the application notes for more information

    Thanks & Regards

    Abhijeet