Questions:

A. What is Errata RMU_E103

B. What devices are affected?

C. How can I prevent this issue from affecting my application?

D. Are there plans to fix this issue?

Answers:

A.

Erratum RMU_E103 describes an issue with certain Series 0 EFM32 devices. Affected parts see a gap in the coverage of the brown-out and power-on reset sources around 1.3V . The exact gap in reset coverage will be part specific if present at all. If an affected device is operating in this problematic VDD range, the device will attempt to start up while well below the tested supply voltage for the microcontroller.

The device takes a short amount of time to start up. For a typical part at normal voltages this is 163 µS. If the startup succeeds, the device will then attempt to execute code, but may not be able to do so at low voltage. At this low voltage neither a successful startup or successful code execution is guaranteed.

Note that during fast voltage ramps, e.g. power-on and power down events, VDD will not be at a problematic voltage long enough for the device to start up. However, if VDD is held at around 1.3V for a sufficient duration, the device may enter this undefined state where code is being executed below tested voltages.

The workaround to this issue is to assert a pin reset during the low VDD event. If a pin reset is asserted, the device cannot attempt to start up. The reset pin should be driven low prior to VDD falling below the BOD reset threshold.

B.

RMU_E103 is an erratum that effects some devices from the following EFM32 Series 0 products:

• EFM32 Zero Gecko
• EFM32 Happy Gecko
• EFM32 Wonder Gecko
• EFM32 Leopard Gecko
• EFM32 Tiny Gecko (Series 0 only)
• EZR32 Happy Gecko
• EZR32 Wonder Gecko
• EZR32 Leopard Gecko

This erratum does not affect EFM32 Gecko, Giant gecko, or any EFM32 Series 1 devices.

C.

Steps can be taken to both detect if RMU_E103 is occurring on a specific device, and to prevent code from executing at low voltage.

• To detect a gap in reset source coverage, Measure the current consumption of the device while gradually lowering VDD. If the device attempts to start up at low voltage, current consumption will increase. The diagram below shows an example VDD waveform that can test for code execution at low voltage and the corresponding spike in current consumption. Note that the current and voltage values are approximate and will vary across parts, applications, and environments.

Figure 1. VDD Test for RMU_E103 Current Consumption

• To avoid code execution at low voltage, avoid slow VDD ramps during normal operation. If the application is likely to experience a slow VDD ramp or see low supply voltage for any significant duration of time, use an external device or user input to assert a pin reset at some VDD level > 1.96V (with sufficient time to engage the internal reset before VDD reaches 1.96V).

Questions:

A. What is Errata RMU_E102?

B. What devices are affected?

C. How can I prevent this issue from affecting my application?

D. Are there plans to fix this issue?

Answers:

A.

Erratum RMU_E102 describes an issue with certain Series 0 EFM32 devices. Affected parts may see voltage regulator failure when subjected to the following scenario:

1. VDD begins to fall due to some external event
2. VDD and Regulator output (DECOUPLE) voltage decay to 0.8-1.2V
3. Power supply to VDD is restored and VDD returns to a nominal value  prior to VDD and DECOUPLE reaching < 0.8V 

In this type of sequence mentioned above , the voltage regulator may fail to re-initialize. If this occurs, the DECOUPLE pin will continue to decay to 0V, even after VDD has recovered. In this state, the core logic is not powered, and the device will be unable to execute code or respond to a pin reset. An affected device will successfully recover from this state if power cycled.

Additionally, if a pin reset is applied prior to the Brown out detector (BOD) asserting reset, the regulator will always re-initialize successfully. The BOD threshold varies between 1.74-1.96V, so a pin reset should be asserted before VDD drops below 1.96V. The pin-reset should be held low until VDD is >1.98V, which is the maximum power-on reset threshold.

The diagrams below demonstrate an example VDD waveform that can cause the regulator initialization to fail.

Figure 1. VDD Decay and Recovery

This figure shows the proper recovery sequence, or what will happen to a working device (not affected by RMU_E102) when VDD falls to 0.9V. Here, the regulator restarts after VDD is restored, and the DECOUPLE voltage returns to 1.8V.

Figure 2. VDD Decay and DECOUPLE failure

This figure shows the failure mode for a device affected by RMU_E102 when VDD falls to 0.9V. As you can see the regulator fails to re-initialize properly, and the DECOUPLE voltage continues to fall until reaching 0V. At this point a power-on reset must be performed to recover the device.

As mentioned above, there are two workarounds to the issue.

• For a device that is already in lock-up, perform a power cycle to recover to a normal state. To do this VDD must be driven to 0V before powering back on.
• For a device that may experience a drop in VDD to 0.8-1.2V, use an external device or user input to assert a pin reset at some VDD level > 1.96V (with sufficient time to engage the internal reset before VDD reaches 1.96V). Additionally, the reset should be held low until power is reconnected and VDD is greater than 1.98V.

B.

RMU_E102 is an erratum that effects some devices from the following EFM32 Series 0 products:

• EFM32 Zero Gecko
• EFM32 Happy Gecko
• EFM32 Wonder Gecko
• EFM32 Leopard Gecko
• EFM32 Tiny Gecko (Series 0 only)
• EZR32 Happy Gecko
• EZR32 Wonder Gecko
• EZR32 Leopard Gecko

This erratum does not affect EFM32 Gecko, Giant Gecko, or any EFM32 Series 1 devices.

C.

To avoid issues caused by RMU_E102, the following precautions should be taken.

• Avoid and check for intermittent battery or power supply connections to VDD. The issue was originally discovered in situations where a loose battery connection during assembly caused VDD to repeatedly drop to ~.9V and then recover to a nominal value. This represents a worst-case scenario for inducing RMU_E102, as multiple VDD disconnections occurred within a very short time frame.
• If your application is likely to experience frequent disconnects from the power supply, ensure that the reset pin is driven low prior to disconnecting.