nrf52840 Dongle burning out - Running 3V on VBUS, drawing 60mA

[nordicnoob]

I have had 3 nrf52840 dongles burn out after a few weeks running on 3V from 2x 1.5 alkaline batteries, powering the dongle from VBUS.  Initially, the current draw was 900uA at its peak, but after a few weeks running idle on the batteries, the dongle started drawing a 60mA, but appears to be fully functional otherwise.  I can connect and interact with the read / write characteristics and I can measure an output on the correct GPIO pins via multimeter readings.  I used a multimeter to measure power from battery to VBUS (not accurate the but the reading is still an order of magnitude off).

I have a couple working theories but would appreciate any insights.

1.  Over time the VBUS input dropped to 2.49V over a couple weeks time.  I read conflicting info about the acceptable VBUS input range, but it one theory is that the voltage dropped too low and the internal voltage regulator started drawing too much current, possibly for weeks.  I switched power input to VDD, cut SB1, and soldered SB2 but the current draw is still 60mA sitting idle.  

2.  Could the advertising settings in the Blinky BLE firmware make the dongle advertise non-stop and could this burn out the voltage regulator in the chip? 

I modified the Blinky BLE firmware to run on the 52840 dongle with a few more read/write characteristics.  I kept the advertising the same as in the example.  Namely the following for reference: 

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(100, UNIT_1_25_MS) 

#define MAX_CONN_INTERVAL MSEC_TO_UNITS(200, UNIT_1_25_MS)

#define SLAVE_LATENCY 0 

#define CONN_SUP_TIMEOUT MSEC_TO_UNITS(4000, UNIT_10_MS) 

#define FIRST_CONN_PARAMS_UPDATE_DELAY APP_TIMER_TICKS(20000) 

#define NEXT_CONN_PARAMS_UPDATE_DELAY APP_TIMER_TICKS(5000) 

#define MAX_CONN_PARAMS_UPDATE_COUNT 3 

#define APP_ADV_INTERVAL 64 

#define APP_ADV_DURATION BLE_GAP_ADV_TIMEOUT_GENERAL_UNLIMITED 

I am also using high output on the GPIO pins to trigger a transistor, configured as follows:

nrf_gpio_cfg(

Pin1,

NRF_GPIO_PIN_DIR_OUTPUT,

NRF_GPIO_PIN_INPUT_DISCONNECT,

NRF_GPIO_PIN_NOPULL,

NRF_GPIO_PIN_H0H1,

NRF_GPIO_PIN_NOSENSE);

[Simonr]

Hi

Can you provide some details as to how you're powering the dongles exactly? 60mA is incredibly high, and is likely due to you supplying the VBUS with too low of a voltage. As stated in the USB supply section of the nRF52840 PS you need to use a 5V supply when using the USB peripheral, as an internal voltage regulator is used to convert the VBUS supply to 3.3V. When using a supply lower than 5V that might damage the USB peripheral I'm afraid.

Best regards,

Simon