BLE getting disconnected when vibration motor is ON with varying different PWM cycles and works at only HIGH/LOW Input signal without disconnection

[KrishNa]

Hello Nordic Team,

We are currently working on a project that has nrf51822 and currently in the production stage. We are facing an issue with Bluetooth getting disconnected when vibration motor is turned on with varying PWM cycles. When vibration starts, after few seconds, bluetooth connection drops and reconnects again. but not facing the disconnection issue with only HIGH/LOW signal.

Attaching the vibration motor circuit image for your reference

Circuit Description:

Vibration Motor Circuit.

xcOUT -> LiPO battery Input

NRF_VIBRATION -> PWM Input from NRFIC

Vibration motor is very far end from any crystal of NRF51822 ( ~ more than 25mm ) ( PCB is 6 layer board with middle ground pour layer and @ edge of PCB’s )

Referred to a similar post from nordic forum   

devzone.nordicsemi.com/.../ble-is-getting-disconnected-when-the-motor-is-turned-on-in-nrf52832-circuit

We have tried few modifications as below

Added / Modified Decaps on Input side of xcOUT :: Result no Change

Modified AGND DECAP for NRF with 1uF :: Result no change ( AIN pin for NRF51822 )

We are currently in production phase and requires quick support to resolve this issue at the earliest.

Thanks in advance.

Best,

Krish

[awneil]

Have you checked your power supply lines with a scope - are they clean, not drooping, etc?

[KrishNa]

Hi Awneil,

Thanks for your reply. Yes, we have checked the power supply lines near the decaps and they are stable without any dips.

Any other parameters you want us to check?

[ketiljo]

You need to check if it's the vibrations from the motor or the noise from the motor that causes this. Can you separate the motor physically from the PCB? Does this still make it disconnect?

[KrishNa]

Hello Ketiljo,

We did the separation of motor with long wires and separated the motor from PCB and it still disconnects.

[ketiljo]

Ok, so it's noise from the motor PCB then. You must see if you can decouple this noise with relativily small capacitors over the motor windings, on the power supply etc. Try with ferrite beads in the motor and radio power supply lines.