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TL750M-Q1: The question of TL750M-Q1 about the input current vs input voltage

Maksim Liu
Prodigy 160 points
Part Number: TL750M-Q1

Hi team,

          I can't understand  input current vs input voltage characteristic that is  TL750's typical characteristic. In datasheet, we can find below figure:

 I have 3 questions:

1, If input voltage is below than min voltage, What will happen to the output?

2, When input voltage is below than min voltage, why the input current increase as input voltage increase?

3, If Io=0A, that is to say, it has no load. What are the input voltage  vs input current curve?

Now, I use 50ohm resistor to serial with TL750's input, and the power supply is 12V. I find the TL750's input voltage is only 4V, and the resistor's voltage is 8V. TL750 can't work normally.

I know I can decrease the resistance to avoid this situation. 

But I want to know the reason of this phenomenon. After all, other P2P LDO havn't this problem. 

Thank you.

 

  • 0
    TI__Mastermind 23361 points

    Hi Maksim, 

    1. Please see this chart for output voltage vs input.

    \

    2. I understand this high current consumption during dropout is not preferred. But this is due to the design. The datasheet did not provide detailed diagram, but usually the high current during dropout can be caused with biasing circuit.

    3. Even you have 0mA of load, I would think the input current vs input voltage plot won't change much from Figure 6, it's probably slightly lower by 10mA due to the load. 

    During the dropout, an input voltage change from 3V to 4V may change the current from 0mA to ~100mA. The estimated input impedance can be calculated by R = delta V / delta I = 1V / 0.10A = 10 Ohms. Due to this reason, when you have a 50 Ohms in serial with it, due to the low equivalent input impedance, most voltage will be divided on the 50 Ohms resistor. 

    Regards, 
    Jason Song