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LP2951 Minimum Current Limit

Hirotsugu Kobayashi
Mastermind 8885 points
Other Parts Discussed in Thread: LP2951

What value is the Minimm Current Limit of LP2951?

  • 0
    TI__Guru*** 145236 points

    Hirotsugu-san,

    If question is what is minimum load current needed for regulation; The data sheet and expected test coverage has a minimum load of 100uA. However, the sense pin resistor load by having pins 1 and 2 connected together is sufficient so no external load is required.

    If the question is how much output current is available; The current limit may engage at as low as 101mA. 

  • 0 in reply to Ron Michallick
    Prodigy 80 points

    Hi Ron,

    I found the Forum on TI LP2951 and I have some questions, could you please help and give suggestions?

    I am using LP2951, printing on the chip is: KY5150 43M, I am not sure what that means though I order the part as LP2951 through Digikey USA.    But, here is the problem I am having:

    I use it as an Adjustable regulator by constructing the voltage divider to give me a constant 5.5VDC output.    R1 (the one connected to Output) is about 3.55K and R2(the lower one and is connected to GND).   The Voltage divider is then tied to Feedback.    Pin 2, 3 and 5 are all open since I don't need Shutdown, Vtap or Vsense.     Next, my application requires that the 5.5V from my regulator to be capable of driving a load of 220 Ohm for a current of 25mA.    I tested and see that if my Input Voltage is between 6.0VDC to 14VDC it is ok, but if I increase my Input Voltage beyond 14-15VDC to 28VDC, the chip gets hot.    If I don't have my load, the chip is ok and works fine from 6VDC to 28VDC What is the possible cause of this Ron?  Does my voltage divider needs to be looked at ?   By the way, based on my design, I must set up the Regulator to only work at 6.0VDC min. to 28VDC max. for a max load current of 25mA.   Is it possible for this LP2951?.  Thank you.

  • 0 in reply to Steven Ngo
    TI__Guru*** 145236 points

    Steven,

    With 28V input and 5.5V output the device will reduce the input voltage by 22.5V and turn the voltage loss into heat just like a resistor would. The current is 25mA, so the power dissipated by the LP2951 is 22.5V*25mA= 563mW. A SOIC package has a 97C/W TJa (thernal resistance). The increase in temperature should be 563mW*97C/W = 55C hotter. Most of the heat leaves the device though the device leads, so the top of case won't be much cooler than the silicon die.

    It is normal for the device to get hot. However it is suggested to keep the die below 105C to improve longevity.

     

  • 0 in reply to Ron Michallick
    Prodigy 80 points

    Hi Ron,

    Thank you for your answer and suggestion.   I agree that we should keep the Temp. below 105C for smooth operation in the circuit.   With 55 degree C hotter, I don't feel comfortable and confident putting it in my circuit.

    If I have to use that 5.5VDc output for my 25mA load and the input voltage range is 6VDC-28VDC, is there any other chip that is equivalent to my requirements that you can recommend?      Thank you.

  • 0 in reply to Steven Ngo
    TI__Guru*** 145236 points

    Steven this is now simple to do.

    Go to ti.com

    Fill in Webench parameters like this then click start design. 
    For low cost there is LP2951 at 27 cent BOM and 19% efficiency (hot running)
    Next in line is a 75 Cent 80% efficient solution. (much cooler)