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TL074H: Short-Circuit Current

Brian Wang0928
Genius 11610 points
Part Number: TL074H
Other Parts Discussed in Thread: TL074,

Here there some questions about the Short-Circuit Current. 

1. In the datasheet, it says there is a short-circuit protection? WHat's kind of the protection? Thermal shunt down?

2. What's the limitation for the short-circuit protection?

Regards

Brian W

  • 0
    Guru 140200 points

    Hi Brian,

    this is a plain current limitation:

    During short circuit condition the output stage goes into class B operation and only one output transistor is conducting all the short circuit current. Output current limitation sets in when the voltage drop across the involved 64R resistor exceeds 2 x 0.65V = 1.3V. Then the two transistors at the left turn-on and limit the base emitter voltage of output transistor. As consequene the output current can longer rise and becomes limited.

    Kai

  • 0
    TI__Guru*** 139956 points

    Brian,

    The TL074H is new design, the current limit is active opposed to legacy TL074 resistive method.

    The short circuit limitations are mentioned in note 2 of absolute maximum table. Short to ground (mid supply) and just one channel at a time.

    I am not aware of shutdown for over temperature. Shorts should be avoided if possible. Generally survivable for a unlikely rare fault, but shouldn't be part of normal operation.

    Here is sample data for VOH and VOL output voltage loss that shows the current limit 

    Six different Vs (supply voltage)

  • 0 in reply to Ron Michallick
    TI__Genius 11610 points

    Thanks for diagram of the current limit. I've few questions to your answer.

    1. What's the effective method to make current limit as you said it's an active? What's the benefit of the active comparing to resistive method?

    2. Is there over temp protection in the TL074H? If so, what's the trigger threshold of the Over temp?

    3. In the note 2 of the d/s, it means only one channel OPA is allowed to be shorting to Ground. What if there are more than 1ch OPA in one package shorting to GND?

    Regards

    Brian W

  • 0 in reply to Brian Wang0928
    TI__Guru*** 139956 points

    Brian,

    1) In active limit current is sensed and the output transistor drive is reduced to limit current. This give a more defined current limit. Resistive current limit changes with the voltage of the resistor.

    2) The data sheet doesn't mention OTP and I didn't see it in some simple overload testing.

    3) The key idea is not overheating the die. Two shorts with a 5V supply is less stressful than one short with 40V supply. Power dissipation is IOUT * V where V is [V+ - VOUT] for sourcing current and is [V- + VOUT] for sinking current.