CC430F5137: Why is there a high inrush current when the microcontroller start-up?

lee Peng

Part Number: CC430F5137

In my application, I need to measure the current consumption of the mcu (cc430f5137). To measure the current of the mcu. I insert a 10ohm resistor at the Vcc. Then, I connect the power supply to the Vcc and observe the voltage across the resistor so that I =V/10. I found that the current at start-up is around 80mA@1.8V and 200mA @3.3V. It will last for a while and decrease gradually. Below is the picture of the waveform under 1.8V and the diagram of the board.

What may cause such a high current at start-up? Is this normal and how to solve this problem?

Regards

over 6 years ago

0 FI over 6 years ago

TI__Mastermind 21430 points

Hi,

I am not sure if the value of current is you are measuring is ok, but there is almost always an inrush current due to the capacitors on the power supply line charging up at power on.

Thanks,

0 lee Peng over 6 years ago in reply to FI

Intellectual 720 points

Thank you. So normally, what is the start-up current for cc430f5137? Can I include this inrush current into the calculation of the power consumption?

0 lee Peng over 6 years ago in reply to lee Peng

Intellectual 720 points

I think this method is ok. For example, the Tx current is the same as the value in the datasheet.

0 cb1_mobile over 6 years ago in reply to lee Peng

Guru 117855 points

Greetings,

Is not your, "method of measurement" (somewhat) suspect?

Use of a lower value resistor - or even better - one of this vendor's "INA series" of current monitor ICs - is "sure to reduce" the "R-C constant" which likely "Reduces the magnitude" of your surge current! Note too - that (excessive) power input resistance may impact the MCU's (POR) and/or other start-up behavior...

0 FI over 5 years ago in reply to lee Peng

TI__Mastermind 21430 points

Hi,

As an example of measurement please see the attached app note: http://www.ti.com/lit/an/swra456/swra456.pdf

Thanks

0 cb1_mobile over 5 years ago in reply to FI

Guru 117855 points

Should the board collection - described just above - be judged (somewhat) as "Over-KILL" (due to the extent of Cost, Time & Effort to Understand, Master & Deploy) - there exists an "Eval Board" bearing (this vendor's highly capable, "INA-260" Current Sense IC) - available at "Digikey" - for 9.95 (USD).

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CC430F5137: Why is there a high inrush current when the microcontroller start-up?