What are the items for the absolute maximum rating in technical datasheet of the diode?

Absolute maximum ratings are the maximum values that must not be exceeded even momentarily to guarantee the life and reliability of the device. It mainly regulates voltage, current, temperature, etc.

Significance of maximum ratings
For diodes, the maximum allowable current, reverse voltage, power dissipation, and other characteristics are specified as maximum ratings.
In circuit design using semiconductors, understanding maximum ratings is very important in order to obtain the best performance from devices and maintain device reliability throughout the target operating life.
In order to guarantee the product life and reliability of devices, absolute maximum ratings must not be exceeded even instantaneously. Maximum rated values are determined by the materials, chip size, package, device design, and manufacturing conditions. For diodes, the maximum ratings in datasheets etc. are the absolute maximum ratings.
They are specified at an ambient temperature of 25°C unless otherwise specified.

Voltage ratings

  1. Reverse voltage ratings
    • Reverse voltage (VR): Maximum DC voltage that can be applied in the reverse direction
    • Repetitive peak reverse voltage (VRRM): Maximum allowable instantaneous voltage that can be applied repeatedly in the reverse direction
    • Peak reverse voltage (VRM): Peak voltage of an AC signal that can be applied in the reverse direction, with its RMS value being less than VR

Current ratings

  1. The following parameters specify the maximum current that can be repeatedly applied to a diode. These parameters are restricted by Tj(max).
    • Average forward current (IF(AV)): Maximum average current of a half sine wave (with a conduction angle of 180°) at the utility frequency (50 Hz or 60 Hz) or average rectangular forward current under the specified conditions
    • Average forward current (IO): Average current of a half sine wave at the utility frequency (50 Hz or 60 Hz) or maximum DC current under the specified conditions
    • Forward DC current (IF(DC)): Maximum allowable DC current in the forward direction under the specified conditions
    • Forward pulse current (IFP): Maximum value of rectangular pulse current in the forward direction under the specified conditions
  2. Instantaneous overcurrent ratings: Surge current that a diode can tolerate only once under the conditions specified in a datasheet
    • Non-repetitive peak forward surge current / peak one-cycle (IFSM): Maximum allowable half-sine-wave or rectangular current at 50 Hz that a diode can tolerate for one cycle (10 ms) without being destroyed. This rating is for a single-shot sine or rectangular wave, not for repetitive current application.
    • I2t limit value (I2t): Maximum non-repetitive forward current can flow with a single half-sine wave with a pulse width of 10 ms or less. It can be calculated as follows from non-repetitive peak forward surge current (IFSM) and pulse width (t):

      I2 x t = ( IFSM / √2 )2 x 0.01  (A2s)

      I: Average current during conduction
      t: Pulse width

Temperature ratings

  1. Junction temperature (Tj): Maximum temperature at the pn junction of pn junction diodes or the metal-semiconductor junction of Schottky barrier diodes at which they operate. The materials of a diode and their reliability determine the maximum junction temperature, Tj(max). The junction temperature, Tj, must be considered not only in terms of the functional operation of the diode but also in terms of its reliability such as device degradation and product life. Generally, degradation of the diode accelerates as the junction temperature increases. The average life in hours of operation, Lm, and the junction temperature in Kelvin (K), Tj, have the following equation relationship. Here, A and B are element-specific constants.
    Log Lm ≅ A + B / TJ
    The junction temperature rating is determined in such a manner as to achieve the target product life.
  2. Storage temperature (Tstg): Temperature range in which a diode can be stored without voltage application. The properties and reliability of the materials that constitute the devices except those of a silicon chip determine the storage temperature range. In addition, when storing care should also be taken to prevent oxidation of diode terminals.

Other characteristics

  1. Isolation voltage (VISO(RMS) or Vdis): For diodes housed in a fully molded package*1, isolation voltage represents the level of electrical isolation between the surface of mold resin and electrode terminals. To confirm the VISO(RMS) (Vdis) characteristic, the diode is tested by applying AC voltage for a specified period of time.
    Isolation voltage is specified as the RMS of AC voltage.
  2. Power dissipation (P or PD): Maximum power that can be continuously dissipated under the specified heat dissipation conditions and the ambient temperature.
    Normally, the power dissipation rating is determined by junction temperature (Tj), ambient temperature (Ta), and junction-to-ambient thermal resistance (Rth(j-a)):
    P = (Tj – Ta ) / Rth(j-a)
    The transient power dissipation (PP or PD) is calculated as follows using the transient thermal resistance value shown in the diode datasheet:
    PP = ( Tj -25 ) / Rth(j-a)(t)
    In the case of relatively large diodes to which a heatsink can be attached, the maximum transient power dissipation is normally determined by junction temperature (Tj), ambient temperature (Ta), and junction-to-case (junction-to-infinite heatsink) thermal resistance (Rth(j-c)).
    PD = ( Tj – 25 ) / Rth(j-c)          PDP = (Tj – 25 ) / Rth(j-c)(t)
  3. Mounting torque (TOR): Maximum torque that can be applied when mounting a diode using screws with a washer through its screw holes.
    When attaching diodes on a thermal fin, the specified mounting torque must be followed. If the torque is too low, the mounting screws will loosen. If the torque is too high, the device could be damaged.

*1: Insulated package in which the entire package is covered with mold resin

An example of absolute maximum rating items in diode technical data is shown below.

Characteristics Symbol Rating Unit
Repetitive peak reverse voltage VRRM 400 V
Average forward current (Note 1) IF(AV) 0.4 A
Non-repetitive peak forward surge current (Note 2) IFSM 8 A
Forward pulse current (Note 3) IFP 14 A
Junction temperature Tj 150 °C
Storage temperature Tstg -55 to 150 °C

Note: Using continuously under heavy loads (e.g. the application of high temperature/current/voltage and the significant change in temperature, etc.) may cause this product to decrease in the reliability significantly even if the operating conditions (i.e. operating temperature/current/voltage, etc.) are within the absolute maximum ratings.
Please design the appropriate reliability upon reviewing the Toshiba Semiconductor Reliability Handbook ("Handling Precautions"/"Derating Concept and Methods") and individual reliability data (i.e. reliability test report and estimated failure rate, etc).

Note 1: Ta = 114 °C, device mounted on a ceramic board, Half sine waveform (α = 180°), 
(board size: 50 mm x 50 mm, soldering land size: 2 mm x 2 mm, board thickness: 0.64 mm)
Note 2: f = 50 Hz, half-sine wave, non-repetitive
Note 3: t = 1ms, Rectangular wave

In addition, some diodes have individual maximum ratings. See the application note below for details.

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