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Original question:

LM185-1.2QML-SP: Package lid (metal body) connection

LM185-1.2QML-SP: 5962R8759461VXA

Bob Wasley
Prodigy 50 points

Part Number: LM185-1.2QML-SP

Tool/software:

Questions to ask TI regarding LM185-1.2 (5962R8759461VXA)

  1. If the voltage reference diode is installed backwards and is forward biased for the life of the part, is there any impact on its mission life?
  2. In this configuration, it is operating with a fwd current of 1.3mA. Can we use the following specs from the datasheet as evidence that the part will not be degraded in this mode of operation?

Absolute Maximum Ratings:

Forward Current:  10 mA

LM185-1.2 Electrical Characteristics DC Parameters

VF  Forward Bias Voltage, IF = 2 mA:  Min.= -1.0V,  Max = -0.4V

There is particular concern with the above questions from the LM185-1.2qml-sp datasheet Schematic Diagram Ref Des Q14 as the transistor base and collector are tied to the diode anode.

  • 0
    TI__Intellectual 1475 points

    Hi Bob,

    The datasheet seems to allow this mode based upon the same specs mentioned in your post. However, I'll need to do more research to determine if this mode is safe for the device as forward biased is not the device's intended use. I will get back to you with an update by early next week.

    Thanks,
    Elizabeth

  • 0 in reply to Elizabeth Won
    Prodigy 50 points

    We have completed more research which has raised related questions.  It is vital we get a timely response.  The issue is escalating to the corporate level due to the importance:

    When the LM185-1.2 is installed backwards there is a measured ~0.7V drop with a fwd current of 1.3mA. What is the path for this current? Is there a Zener diode in the design that is not shown on the LM185-1.2 notional schematic in the datasheet?  Note that the LM185-ADJ commercial part has a notional schematic that shows a 6.3V Zener diode. If the Flight part has a similar diode, that could explain the measurements and the datasheet entry for electrical characteristics.  

    If there is a Zener diode in the device, is it that where the electrical V forward specifications of the design come from?  i.e. that can tolerate the 10mA max forward current with a minimum forward junction voltage of 0.4V at I forward 2 mA?

  • 0 in reply to Bob Wasley
    Prodigy 50 points

    We urgently need a response.  Are the device specifications for Forward current and voltage driven by the not shown in the schematic ZENER diode?

  • 0 in reply to Bob Wasley
    TI__Intellectual 1475 points

    Hi Bob,

    Due to the age of the part (40+ years), we don't have any documentation to provide more information on this topic besides the schematic provided in the datasheet and therefore have no ability to simulate or further analyze the part. HTOL and Burn-in life tests are not biased in the forward condition, and there is no data on operating life in this unintended condition. We can continue to work with you through TI's contact for you regarding this matter.

    Thanks,
    Elizabeth