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ADC088S022: About ADC088S022 Input Port Protection Solution

SHENG YANG
Expert 1320 points
Part Number: ADC088S022

Hi team.

As shown in the figure below, the ADC088S022 input port integrates diodes D1 and D2, and the documentation states that these are ESD protection diodes. Could you please provide the specifications of these diodes, such as ESD Vrwm, Vbr, Vc, and any other relevant parameters? What level of electrostatic discharge (ESD) can these diodes withstand? Can D1 and D2 be used as input clamp diodes? Should I include additional voltage clamp diodes at the input for my design?

  • 0
    TI__Expert 8625 points

    Hi Sheng,

    Thanks for your question. As these are older National Semiconductor devices and the datasheet does not specify those parameters, I do not have that information. We do recommend external voltage clamps if your application will see values outside the absolute maximum ratings. The ESD diodes are only to protect from ESD events. The ESD susceptibility values can be found below:

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    Expert 1320 points

    H.

    Thank you for your response.

    As shown in the figure below, according to the datasheet, the operating range of the analog input is 0 V to VA. Exceeding this range will cause the ESD diode to conduct and result in unstable operation. Does this voltage range refer to the range of electrostatic protection or does it mean that the ESD diode will protect and conduct above the VA maximum? The point I am trying to make is whether the ESD diode has clamp protection or not? Can you confirm this for me?Thank you .

    Description of what you answered above. The voltage level of electrostatic protection is very high, and if a diode is used as a clamping protection circuit, the protection voltage is generally only one diode voltage drop higher than the maximum VA. 

  • +1 in reply to SHENG YANG
    TI__Expert 8625 points

    Hi Sheng,

    Yes, it will protect against violations of the max spec for a short duration of time (typically well under a microsecond in duration). However, turning on the ESD diode repeatedly could affect the lifetime of the device, so we do not recommend depending on the ESD diode for protection if your application is due to see voltages above the max specification often.

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    Expert 1320 points

    Hi.

    Thank you for your response.

    1、Can I understand that the internal ESD diode also has the function of voltage clamp protection?

    2、If the ESD diode is in a long-term on-state like the clamp diode, is it also necessary to series a resistor in the circuit? To limit the current?

  • 0 in reply to SHENG YANG
    TI__Expert 8625 points

    Hi Sheng,

    The ESD diode will turn on and protect from violations of the max ratings, but it only expects to do so for well under a microsecond. Past this, the lifetime of the device may be impacted so we recommend adding an external clamp if your application will see violations of the max rating often.

    Please do not leave the ESD diode in long-term on-state. The current into the device should always be within these limits to avoid damaging the device:

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    Expert 1320 points

    Hi.

    Thank you for your response.

    1、If I put a series resistor in the pin input to ensure that the current does not exceed the maximum input allowable current. Can ESD diodes be used as clamping diodes?Because of the reasons for cost reduction, it is hoped that if ESD tubes can achieve the requirements of clamp voltage protection, it is still hoped that the external clamp diode can be eliminated.My actual input voltage is 5V Max, but it will be fed to the port of the ADC after two 1K resistors. As shown in the following picture.

    2、The opening time limit of 1us mentioned in the above reply is explained in the chip data manual？

  • 0 in reply to SHENG YANG
    TI__Expert 8625 points

    Hi Sheng,

    If your input voltage is 2.5V, then you should be fine. Current limiting the input signal to avoid violating the max current limits is a good idea. Since your VA = 3.3V, if the input signal goes beyond 3.3V, the ESD diodes will conduct and this may result in erratic operation of the ADC. I don’t think this is likely if your input signal is fixed.

    The microsecond duration is not mentioned in the datasheet. It is an estimate from another engineer who worked with these parts in the past.

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    Expert 1320 points

    Hi.

    Thank you for your response.

    1、If I have a resistor in series at the input port to limit the current, then the ESD diode can be used as a clamp diode？

    2、It does not matter if the input voltage exceeds VA and the ESD diode starts causing the ADC to operate erratically. As long as the ADC chip is not damaged.

    3、So according to my idea, the port series resistor limits the maximum current, through the internal ESD diode to achieve voltage clamping and electrostatic protection, this solution is OK? It does not matter if the work is not stable, as long as the ADC chip is not damaged.

  • 0 in reply to SHENG YANG
    TI__Expert 8625 points

    Hi Sheng,

    Will your circuit input go beyond 6.5V (max VA specification)? Even if current is limited, if input voltage > 6.5V (max VA) often, the device may be damaged over time.

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    Expert 1320 points

    Hi.

    Thank you for your response.

    The power supply of my ADC is 3.3V, and 3.3V is obtained from DCDC with 5V input, while 5V is obtained from DCDC with 12-24VDC input.  I think the maximum input voltage VA will not reach 6.5V, and there is a small probability that it is 5V input.  There may be some kind of circuit anomaly such as the input resistance is short-circuited, causing the 5V input voltage to be directly connected to the ADC port

  • +1 in reply to SHENG YANG
    TI__Expert 8625 points

    Hi Sheng,

    The ESD protection will not act as a voltage clamp. Please use an external voltage clamp.

    Best,

    Samiha