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

[Øyvind Karlsen]

Did you heed the following sentence from the MCP1802T datasheet?

The minimum VIN must meet two conditions: VIN>=2.0V and VIN >=(VR + 1.0V). Where VR is the output voltage.

I'm not sure of the workings of this particular LDO, but could it be possible that it enters an unspecified state when the input voltage gets low?

Could you try probing the output voltage from the MCP1802 device?

Best regards,

Øyvind