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INA828: Technical inquiries regarding the use of INA828

Grady Lee
Genius 4215 points
Part Number: INA828

Hi, TI expert

A customer company is mass producing a product using INA828, but a problem has occurred and I have a technical inquiry.

For more information, please check the circuit diagram and problem details in the attached document (PPT) below.

INA828ID IC floating inquiry.pptx

The contents of the attachment are as follows.

- When the voltage source is OPEN (circuit floating), the voltage is charged to the condenser due to noise coming through the Voltage Sensing Cable (BATT+, BATT-), and a stray voltage is measured. (It was confirmed that stray voltage (3 ~ 5V) is measured)

- The problem was solved by inserting a full down RES into the relevant area, and the voltage rise can be confirmed through testing, but technical documentation is required to confirm that there is no problem.

- Customer request:
Q1) It is necessary to check how far the stray voltage rises.

Q2)  I need evidence that the INA828ID will not be damaged when the voltage rises above 12V due to the floating circuit. Is it possible to provide a technical explanation?

Q3) Based on the voltage rating in the spec section of the datasheet, I don't think there will be any problems, is that correct?

Q4) Is there any technical data that can be used as a basis for the above?

Please answer the 4 questions above. Thank you.

  • +1
    TI__Mastermind 24618 points

    Grady,

    Here are answers to your questions:

    Q1) It is necessary to check how far the stray voltage rises.  No.  It is expected that the input of an amplifier will float.  This condition is expected to happen to all amplifiers, so it is important to make sure that a float on the input does not cause damage.  In general, floating the input will cause the output signal to drive to either the positive or negative supply rail.  The device is not functioning as an amplifier with the inputs floating, but the device will not be damaged by this condition (true in general for amplifiers).

    Q2)  I need evidence that the INA828ID will not be damaged when the voltage rises above 12V due to the floating circuit. Is it possible to provide a technical explanation?  As I mentioned above, this condition is expected for all amplifiers.  The concern for damaging devices comes from the application of external signals that violate the absolute maximum rating of the amplifier.  The voltage on a floating input is internal voltages that feed through the ESD protection devices.  You will notice that the voltage on the input never exceeds the power supplies of the device.  Most devices have a absolute maximum voltage rating on the input that is 0.3V above the power supply.  This rating comes from the fact that applying external signals above this voltage will turn on the ESD structures and potentially cause a large current that will damage the device.  For the INA828 the amplifier has additional protection circuits that actually protect the device significantly above the power supply.  Section 7.3.4 cover the operation of this circuit.  In your case it really don't apply to your situation because the protection is for external signals not a floating input.

    Q3) Based on the voltage rating in the spec section of the datasheet, I don't think there will be any problems, is that correct?  Yes.  You are correct.  In fact, you never need to worry about floating the input damaging an amplifier.  The main concern is external signals that damage the absolute maximum rating of the device.

    Q4) Is there any technical data that can be used as a basis for the above?  Figure 16 shows measured input current with a ±40V input signal applied.  There is no data  for a floating input as all amplifiers are expected to be safe from damage for this condition.

    I hope this helps.  Best regards, Art