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LM2776: LM2776 simulation and test's difference question

Part Number: LM2776
Other Parts Discussed in Thread: TINA-TI

Hi team,

We found a phenomenon in the process of applying LM2776, some doubts, would like to consult:
When using LM2776 as a typical single-stage ChargePump application, through simulation, we found that the VIN current fluctuates, and the frequency is consistent with the internal 2M switching frequency of the chip, which is in line with our understanding of the function diagram in the manual;
But through actual measurement, it is found that the VIN current is stable and continuous, and does not fluctuate intermittently; the actual measurement results are inconsistent with the simulation results, which is very strange.
How to understand this phenomenon? Is there any other design influence in the chip?
The following are our simulation and test results:

[Test result] (about 200mA load, connect a 5Ω resistor before VIN, use a voltage probe to test the voltage drop, and indirectly test the current)

  • Hi Dane,

    One reason you could be seeing that result is because the 5 Ohm resistor could be placed between the input supply and the input capacitor, and not between the capacitor and the input of the converter. Thus you are measuring the current through the input power supply and not the current at the input of the converter. The input current (AC+DC components) of the converter is equal to the sum of the current coming from the power supply (DC component) and the current coming from the input capacitor (AC component).
    Can you send a picture of your test setup so we can verify the placement of the resistor?

    Also please send the TINA-TI simulation file you linked in the first message.

    Regards,
    Davor

  • Hi Dane,

    Do you have any updates? 
    Is the problem resolved now?

    Regards,
    Davor