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TLV8541: Power Consumption

Giuseppe Leotta
Prodigy 130 points
Part Number: TLV8541

Hi,
I would to use the TLV8541 on my application. It's used on as a comparator to wake up the microcontroller. On the non-inverting input there is the reference voltage, in the other input there is the analog voltage. When the analog voltage i major than the reference voltage the output goes on. It's very easy. The problem is the power consumption, this op-amp seems to absorbe 400uA. I tested it when the analog input is 0V then the output is 0V. The power supply of the op-amp is 2.7V, the reference voltage is 0.7V. If I remove it the current is lower of 400uA. It's possible this power consumption?

Regards

  • 0
    TI__Guru*** 149086 points

    Hello Giuseppe,

    TLV8541 supply current will be much lower than 400uA. Removing the op amp will remove the quiescent current for the op amp, but it will also remove power from the load on the output node of the op amp. The application state can also change which will change supply current.

    For an op amp removed test with 0.7V on non-inverting input and 0V on inverting input, connect output node to 2.7V to simulate an op amp being there that uses zero quiescent current. This test will be a fair comparison.

    Does this happen on more than one application board?  

  • 0 in reply to Ron Michallick
    Prodigy 130 points

    Dear Ronald,
    thank you for reply.
    I'm sorry but I don't understand. If the conditions are n-inv IN 0,7V, inv IN 0V, out 0V, what is the power consumption of the op-amp in these conditions?
    The output of the op-amp goes into an digital input of a microcontroller.
    If I remove the op-amp in these conditions I don't alterate the system, the non inverting input is high impedance, the other input is 0V and the output is 0V, there isn't current.
    Why I need to put the output to 2,7V?
    Thank you
    Giuseppe

  • 0 in reply to Giuseppe Leotta
    TI__Guru*** 149086 points

    Giuseppe,

    Non Inverting voltage = +0.7V > 0V = inverting voltage ; that will result in a high output, not low. Is your output accidently shorted to ground?

    I did check supply current for all supply voltage and linear and comparators mode at varied common mode and current was normal (only a little difference) 

  • 0 in reply to Ron Michallick
    Prodigy 130 points

    Dear Ronald,

    I'm sorry, I wrong to write. 0,7V reference voltage is applied to the inverting input and 0V to the non inverting input.

    If the voltage to the non-inverting becomes highter of 0,7V the output goes high. Otherwise it stay at 0V. In these conditions the op-amp seems to absorb 400uA.
    What do you suggest?

    Best Regards.

    Giuseppe

  • 0 in reply to Giuseppe Leotta
    TI__Guru*** 149086 points

    Giuseppe,

    The op amp current at 2.7V supply is little lower in the output low (or high state) than it is in normal linear operation, so the comparator mode is fine. The data sheet has a PIR example where two of the op amps are comparators. 

    I see two possibilities, one is that the op amp is damaged and draws 400uA; the other possibilities it that the output load current and other downstream circuits draw 400uA.

    So measure supply current with the output in the normal low state (A). Then remove the op amp, measure current again (B) and measure output node voltage too (V). Finally short output pin node to ground. Measure the supply current once again (C)

    The op amp quiescent current is A-C. I know A-B is 400uA, but I don't know what the output node does with the op amp removed.

    Tell me the [A,B,C,V] results and show me what is connected to the output node.

  • 0 in reply to Ron Michallick
    Prodigy 130 points

    Dear Ronald,
    thank you very much. I tried as you told and I found that the problem is on the pin of Microcontroller. I'll see how I can solve but the op-amp works fine.
    Best Regards.
    Giuseppe