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[MSP430F5529] shortcircuit or low impedance VCC-GND

Massimo Martucci
Prodigy 10 points
Other Parts Discussed in Thread: MSP430F5529

Hi to everybody,

I'm developing a device using msp430f5529 and I am finding a serious problem without discovering the real cause.

In particular conditions of my application, microcontroller stops to work correctly. I understand this because suddenly there is a overconsumption on micro VCC pin 3.3v (in general VCC of other part of circuit) and it's impossibile to download firmware and continue debug application. If I change the micro with a new-one, the circuit and micro become to work correctly.

There is a battery manangement with a step-up that in a particular condition (battery state) generates the same VCC value present in other condition (main source state).

This problem happened in different conditions, during startup or after several on/off of circuit.

I tried to analyze the faulty micros and I discovered a strange thing. Using a simple multimeter, I measured the impedance between pin DVCC and DVSS (18 e 19 of version MSP430F5529IPN) and it's very low on some faulty micros and near 0 ohm on other faulty micros. Furthermore, if I use multimeter in voltage drop diode measurement, I can see that internal diode voltage drop falled down (eg. between an other pin and DVSS voltage drop is 0.5-0.6V, while between DVCC and DVSS it's 0.2-0.3V).

The same measure made on good programmed micro or "blank" new micro, the impedance is very high.

I suppose some causes:

1) ESD overstress on some pins of micro

2) voltage spike directly on DVCC/AVCC pins (connected together in circuit) or on some other pins

3)  current spike

What can it generate a similar faulty condition of low impendance?

Can maybe the problem arrive on some other pins and generate a faulty condition on DVCC pin?

What I don't understand, I was sure to find also low impedance between AVCC pins and AVSS, but it's not in this way.

I decided to write here to find some suggestions in order discover the real cause.

Thanks

  • 0
    Guru 227245 points

    All I/O and most other pins of any MSP do have clamp diodes. Over-voltage (or negative voltage) on one of these pins will be shorted to DVCC or DVSS These diodes can route up to 2mA rated current. If more is applied for a longer period of time, the diodes will melt, either losing the protection (and frying the port circuitry) or shorting the pin to DVCC(DVSS. However, a short between GND and VCC is rather unlikely. But possible, if a certain pattern of over/under voltage is applied.

    There is also a clamp diode between AVCC and DVCC (and AVSS and DVSS). This one might be still intact, hence the still high impedance between AVCC and AVSS: the diode voltages exceed your measuring voltage - a Multimeter often uses only 2V or less for impedance metering)

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