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MSP430FR2433: MCU resets due to voltage drop.

Part Number: MSP430FR2433

Hi,

I am currently having a problem with a MSP430FR2433 resetting, possibly due to a voltage drop on the supply pin. When a load (2 LDOs and a load switch, about 500 mA) is enabled through the MCU (or manually triggered), the MCU resets. However, the output port (3.0) which enables the load continues to stay high through the reset, so it only happens once.

Supply voltage is 3.377 V and the drop goes down to 2.882 V:

From what I can understand, it is the Supply Voltage Supervisor (SVS) or BOR that causes the reset (5.11.1 in datasheet).

I have tried to add an additional electrolytic capacitor (470µF) at the input of the circuit. Not an optimal position, but board is very small and hard to modify. This reduces the drop to 3.051 V, at a rate just under 0.1V/µs (should be safe from BOR reset due to V change). Without the additional capacitor, the drop is 2.882 V at a rate close to 0.2V/µs (close to BOR trigger).

I am currently running the MCU in LPM0 (SVS active) and have tried lower clock speed without any change (down to 6 Mhz).

Is it possible to adjust the SVS (or BOR) to handle this voltage drop, if so how? Or any other recommendation to resolve my issue?

I followed the recommendation from the datasheet about capacitors at Vcc pin (10µF and 0.1µF), but considering increasing the 10µF capacitor value (size 0805, restricted to maximum 100µF), and possibly the capacitors I have in front of the LDOs.

  • Hi,

    If you have a limited PCB size, why not use a high performance LDO which has a lower voltage drop in this situation. Otherwise, you will need to put more capacitors on the VCC pin.

    Best regards,

    Cash Hao

  • Hi,

    I already use a pair of high performance LDOs that should have a low voltage drop, and both are configured for soft start (1 ms). However, I detected some parasitic capacitance that might disturb the LDO soft start (controlled by a 1 nF capacitor). Together with the load switch, the voltage drop might be higher than the capacitors are able to handle (in front of MCU, LDO and load switch).

    I added a 4.7 µF capacitor to the enable pin (to study the voltage rise/behavior of the enable pin), and increased the VCC pin capacitor of the MCU to 100 µF (instead of the temporary 470 µF on the circuit input). It did solve the problem of the MCU resetting, the extra capacitor on the enable pin might allow enough time between the LDOs and load switch (enables at different voltages). Main issue is probably too low values on the input capacitors in front of the LDOs and load switch, causing the surge.

    Still a bit confused of why the MCU was resetting even when the voltage drop rate was within the margins stated in the datasheet, I am unsure on how/when the SVS (or BOR) works at 3.3V and how the trigger/limits can be configured. However, as the cause of issue have been identified (and I would consider it a hardware problem outside of the MCU) I will mark this as solved.

    Regards,
    Ronnie

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