Possible Ways to Brick?

[Nick]

Hello,

I have a board with an RFDuino on it which uses a Nordic nRF51822 internally. We are seeing a few of them auto-brick when the input voltage dips too low.

My first guess is that it is doing an EEPROM write even when the voltage dips or something, but I am just wondering what can brick these? Any known errata for this?

Basically it is running off of a big battery and as long as it stays above 2.9-ish volts, it works forever it seems. When it goes to 2.8v or so, sometimes it stops responding and then never turns on again. I haven't written the software but I am trying to get the code to look at.

[Øyvind Karlsen]

Hi,

What do you mean by brick, do these devices not turn on again when powered by lab power supplies?

Are you sure that the battery can take the approx 15 mA current spikes (radio TX + cpu active)? You can alleviate this somewhat by adding capacitor reservoirs on the VDD line.

What is probably happening is that your battery is being pulled down from 2.8V by a radio TX current draw, the battery voltage will drop due to not being able to supply the instantaneous current. At 2.8V a coin cell battery is typically at the end of its life.

Best regards,

Øyvind

[Nick]

Yes I am fully aware of how linear regulators work. The nominal battery voltage is between 6v (when it is dead) and more than 8v when fully charged. There is always enough headroom for the 3v LDO and the 5v LDO and the variable 0v-5.5v buck.

I have also looked at it with a lab supply. When the input voltage is decreased, the LDO output voltage tracks downwards with the input until about a diode above ground where it just dies. All perfectly normal.

I also would have no problem with the Nordic chip not working properly when the input voltage gets too low. However, once normal voltage is applied again, it should work again. Right now, it seems like 20% of the time (4/20) the part stops functioning when the voltage gets low (that's OK) but then on the next power cycle when the input voltage is good, it never boots up.

That's what I am trying to figure out, is what could cause the part to not boot up, and what can I probe to see if it is booted. Is there a signal it puts out on the chip antenna to check connectivity that will show up with a scope? Does the reset pin or some other pin have some discernible pattern before, during, or after boot up? Test mode pins?