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LM358: ESD protection diode

user5163865
Genius 3600 points
Part Number: LM358

Hi,

What is the Vf of the ESD protection diode of the LM358?

Customers use in-circuit testers for PCB mounting inspection.

The VF of the input ESD protection diode of the LM358 cannot be read from the DS, but the test result was always about 0.8V.

However, in all recent tests, Vf = 1.2V.

I think the VF of a silicon diode is usually 0.7 to 0.8V, but is 1.2V the correct value for the LM358?

Looking at the latest PCN, the design / wafer size etc. have changed, but the DS specifications have not changed.

I understand that Vf = 0.8V can be 1.2V, but customers are worried that there may be major changes to the IC.

Best regards,

Hiroshi

  • 0
    Guru 140200 points

    Hi Hiroshi,

    as far as I know the standard LM358 does not have ESD protection diodes at the inputs. The pn junction you bias by your measurement is the PNP input transistor of LM358. Eventually, they improved the circuit by adding a current limiting resistor in series to the input on the die?

    Kai

  • 0
    Guru 281490 points

    The diode is not designed to carry large currents, so its forward voltage might increase quickly.

    A different die indeed might change the diode, but not the characteristics of the opamp itself. (But are you sure you didn't look at a different device like the LM358-N or LM358B?)

    Section 2.4 of the Design Guidelines for LM324/LM358 Devices says:

    An input voltage of less than −0.3 V can cause parasitic diode conduction that results in the output assuming the minimum VOL or maximum VOH level. Operation in this region is not defined in the data sheet as it violates the absolute maximum specification for input voltage. The input current turns on internal parasitic NPN transistors that steal current from other internal nodes causing output phase reversal.

    Do not try to determine phase reversal performance empirically as different units may have different performance. Negative inputs must be avoided, assuming a single supply configuration, unless the application can accept either the VOL or VOH level during the duration of the negative input. In cases where a negative input voltage cannot be avoided, use a resistor in series with the input to limit the current to −1 mA or less. This amount of input current is unlikely to cause any damage.

  • +1
    TI__Guru**** 151036 points

    Hello Hiroshi-san,

    Do you have full part numbers?

    -1.2V on an input relative to pin 4 would be over 10mA. That is too high of a current to use.

  • 0 in reply to Ron Michallick
    Genius 3600 points

    Hi all,

    thank you for your answer.
    The full part number is LM358ADGKR.

    Customer's system is working properly.
    The only problem is the ICT inspection process.

    Therefore, there may be an error in the ICT measurement method.

    Customers, including myself, thought this OPAMP had an ESD protection diode.

    Best regards,
    Hiroshi

  • 0 in reply to user5163865
    Genius 3600 points

    I'm sorry.
    I mistakenly set it to "solved".
    Please give me some advice.

  • 0 in reply to user5163865
    TI__Guru**** 151036 points

    User,

    An ESD protection diode means a structure (not always a diode) that is specifically designed to protect against ESD. It provides no other device function. 

    LM358 has no such specific structure. The exception is LM358B and LM358K; they do have such structures.

    Even the normal functional structures (transistors that make an op amp) have some native ESD resistance.

    For all LM358, the diode result is IN to V-  and no IN to V+.   

  • 0 in reply to Ron Michallick
    Genius 3600 points

    Hi,

    Thank you for answering.
    I could understand it.

    When I checked the customer's measurement results, the only thing like diode characteristics was certainly IN to V-.

    According to customer measurements, the voltage drop has long been 0.8V, but with modern LOT it is 1.2V.
    This is a quality issue, but I understand that it's okay because I don't guarantee it in the datasheet.

    Is this a good answer for our customers?

  • 0 in reply to user5163865
    TI__Guru**** 151036 points

    There are two qualified chips that make LM358ADGKR. To get consistent results reduce the in circuit test current. If by chance, the test is OUT to V+ supply don't do that. Do OUT to V- instead.

  • 0 in reply to Ron Michallick
    Genius 3600 points
    Ron Michallick said:
    There are two qualified chips that make LM358ADGKR. To get consistent results reduce the in circuit test current. If by chance, the test is OUT to V+ supply don't do that. Do OUT to V- instead.

    Thank you for answering.
    Ask to reduce the ICT current.

  • 0 in reply to user5163865
    Genius 3600 points

    Hi,

    The problem has been resolved.
    Thank you for your support.

    Best regards,
    Hiroshi