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LP2951-Q1: About each limit when the output is short-circuited

Kaji@PAN
Mastermind 7775 points
Part Number: LP2951-Q1
Other Parts Discussed in Thread: LP2951

Hi,

I would like to ask you about the current and thermal limiting features of the LP2951-Q1 device.
(question 1)
In the circuit shown below, if VOUT is short-circuited with GND, an overcurrent will occur, but it seems that the current is limited at 160mA (typ).
In this case, is constant current controlled at 160mA?
Or will VIN and VOUT be disconnected?
(Question 2)
In the above, when the constant current is controlled at 160mA, the device seems to heat up and reach the thermal limit.
In this case, what is the thermal limit set for this device?
In the thread below, the measured value of EVM seems to be 184 °C, but I would like to know the setting value, not the measured value of this device.
(Question 3)
Is it possible to detect an overcurrent and stop the operation of the device itself?
(Question 4)
I think that each limit works when VOUT is short-circuited to GND and becomes overcurrent. In this case, is there a possibility that this device will smoke and ignite?

Best regards,

  • 0
    TI__Guru 50025 points

    Hello,

    Kaji@PAN said:
    (question 1)
    In the circuit shown below, if VOUT is short-circuited with GND, an overcurrent will occur, but it seems that the current is limited at 160mA (typ).
    In this case, is constant current controlled at 160mA?
    Or will VIN and VOUT be disconnected?

    Yes, in the event of a short-circuit the current will be limited and constant at 160mA (typ). Vin and Vout will be disconnected in the sense that the output current is independent of Vin.

    Kaji@PAN said:
    (Question 2)
    In the above, when the constant current is controlled at 160mA, the device seems to heat up and reach the thermal limit.
    In this case, what is the thermal limit set for this device?

    The abs max junction temperature is listed as 150C, but the actual junction temperature that the thermal protection kicks in at may not be 150C - it may actually be 150-175C. To be safe, it is advised to design such that the thermal protection kicks in at Tj = 150C.

    Kaji@PAN said:
    (Question 3)
    Is it possible to detect an overcurrent and stop the operation of the device itself?

    There is not a built-in feature for this application, but you can use other components like a current sensing amp to detect high current and use the signal to disable the part.

    Kaji@PAN said:
    (Question 4)
    I think that each limit works when VOUT is short-circuited to GND and becomes overcurrent. In this case, is there a possibility that this device will smoke and ignite?

    The thermal shutdown circuitry will prevent this from happening. During thermal shutdown the device will go into an off state where Vout and Iout go to zero. Once the junction temperature has fallen below the lower hysteresis junction temperature, the part will turn back on and resume its overcurrent state (assuming this has not changed) and will again go back into an off state and the cycle will repeat until the fault is gone. 

    Best regards,

    Nick