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MSP430FR5969: Startup current / inrush current.

Benjamin Mlang
Prodigy 50 points
Part Number: MSP430FR5969


Hi Guys!

I'm curious about a "typical" current during start up of the MSP430FR5969. My system is supplied by a energy harvesting source, with selectable output voltage of 1.8V to 4+V, but a maximum output current of 5mA.

Usually the MSP430 is powered by a super cap, but when the super cap voltage is to low, the MSP430 stops working (as it should be). So if power is available from the energy harvesting source, the MSP430 should be powered by it and charge the super cap. The charging of the super cap is controlled by the uC, so there is no current drain on the super cap, which is anyway limited by hardware. So the problem is, when the system voltage is very low, and i try to supply the system by the energy harvesting source. The voltage of the source collapses due to the too high current. With the limited tools i have, i tried to measure the startup current, powered by a lab supply. This experiment led to a current of 15mA (@1,9V) on startup. The duration of the 15mA are not very long, but long enough to prevent start up. Is this a realistic value? Or are there any abnormalities? 

Thank you for your help!

Yours

Benjamin

EDIT:

I'm using the MSP430FR5969 Launchpad as the platform.

  • 0
    TI__Guru 52040 points
    Hello Benjamin,

    What are the pins of the MSP430FR5969 connected to? I am wondering if there are pins connected to external components and before/during pin initialization, the device draws 15 mA.

    Please let me know what the MSP430 is connected to.
  • 0 in reply to Nima Eskandari
    Prodigy 50 points

    Hi Nima!

    Thank you for your answer. I totally forgot to mention, that I'm using the MSP430FR5969 Launchpad. The energy harvesting source is directly connected to Vext of the Launchpad.
    I've also tried to add a small 100nF Capacitor to the supply line, but it did not solve the problem.

    This is the initialization routine for the I/O pins.

    void GPIO_Init()
{      
            // Digital I/O
	GPIO_setAsInputPin(GPIO_PORT_P1, GPIO_PIN2);		// AS3955 IRQ
	GPIO_selectInterruptEdge(GPIO_PORT_P1, GPIO_PIN2, GPIO_LOW_TO_HIGH_TRANSITION);
	GPIO_enableInterrupt(GPIO_PORT_P1, GPIO_PIN2);
	GPIO_setAsOutputPin(GPIO_PORT_P3, GPIO_PIN0);	// AS3955 /SS
	GPIO_setAsOutputPin(GPIO_PORT_P4, GPIO_PIN3);	// load switch

            // Launchpad
	GPIO_setAsInputPinWithPullUpResistor(GPIO_PORT_P4, GPIO_PIN5);	// switch 1
	GPIO_setAsOutputPin(GPIO_PORT_P4, GPIO_PIN6);	// LED 1
	GPIO_setAsInputPinWithPullUpResistor(GPIO_PORT_P1, GPIO_PIN1);	// switch 2
	GPIO_setAsOutputPin(GPIO_PORT_P1, GPIO_PIN0);	// LED 2

            //SPI
	GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P1, GPIO_PIN6, GPIO_SECONDARY_MODULE_FUNCTION);	// MOSI
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P1, GPIO_PIN7, GPIO_SECONDARY_MODULE_FUNCTION);	// MISO
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P2, GPIO_PIN2, GPIO_SECONDARY_MODULE_FUNCTION);	// SCLK
}

    Aside from the Launchpad circuitry and the above mentioned pins, is nothing else. P1.2 is for IRQ of the energy harvesting NFC chip. P3.0 is the slave select line and P4.3 enables the switch for the super cap charging.

    Thank you!

  • 0 in reply to Benjamin Mlang
    TI__Guru 52040 points

    Is it possible to disconnect all the pins, and measure the current? If we could verify that with nothing connected, everything works and the current doesn't spike high, we can connect the external pins one by one to try and isolate the issue.

  • 0 in reply to Nima Eskandari
    Prodigy 50 points

    Sadly, I don't have access to the lab at the moment, due to university vacation. I some how believe the external circuitry is not the reason for this spike. The lines are directly connected to the external chip. According to the datasheet, the maximum input leakage current (at the CMOS inputs) is rated with 10uA (@125°C). And the same behavior is shown with different chips (all the same part). Aside from the in the first post mentioned behavior, everything works fine and as expected. So i would exclude a problem from the chip. But as soon I'm having access to the lab again (2 weeks :-( ), I will give it a try!

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