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Original question:

LMR14020-Q1: Sleep Mode Quiescent Current

LMR14020-Q1: Sleep Mode Input Current Calculation

Stephen Thomas
Intellectual 710 points
Part Number: LMR14020-Q1
Other Parts Discussed in Thread: LMR14020

Hello,

I'm planning to use LMR14020-Q1, where my nominal input voltage will be 12V and I'm planning to set the output voltage at 3.8V. 

I'm using L=4.7uH , and 2 x 22uF as Cout , fsw 1.8MHz , Cin =10uF

In normal cases i may see a load current requirement up to 1.5 - 2A.

But in say a system low power mode the 3.8V output only requires round 3.4mA. 

I understand the LMR14020-Q1 will be in sleep mode at this condition. I want to precisely know how much will be my input current in this situation.

Also if possible how that will be calculated.

Can i go like this say output power is 3.8V x 3.4 mA = 12.92 mW; considering approximately 70% efficiency, Pin= 18.457mW ; with 12V input can i expect Input current =~ 1.53 mA continuous ?

Also do i need to add the standby current or any other pin current to this figure.?

If you can confirm this soon , it will be really helpful.

Awaiting your response.

Thanks

Stephen

  • 0
    TI__Mastermind 23845 points

    Hi Stephen,

    I dont think there is an easy way to calculate the exact input current during light load mode. 

    The reason is because the LMR14020 burst it's PWM frequency during light load mode and as you increase the load, it will increase it's burst frequency until it reaches a nominal operating frequency. But predicting what would be the burst frequency at this light load is quite a challenge and hence calculating the efficiency at this light load.

    What you mentioned above seems reasonable given the efficiency of the converter. The standby current should also been taken into account when you use the efficiency numbers. You may need to substract the inductor series resistance but this number may be small at light load (3.4mA).

    Therefore i think it's worth to do the measurement empirically using a batch of samples and seeing the min and max value to get a good idea of the range input current that you may get based on the specific design configuration (L and C)

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Intellectual 710 points

    Hi Arief,

    Thank you for the reply.

    Arief Hernadi said:
    The standby current should also been taken into account when you use the efficiency numbers

    Is it the IQ= 40uA mentioned as Operating quiescent current (non switching).

    Regards,

    Stephen

  • 0 in reply to Stephen Thomas
    TI__Mastermind 23845 points

    Hi Stephen,

    Yes that is correct. Here is one good article that demystified the currents term that you may encounter while reading the datasheet

    Thanks

    -Arief