$ sudo ./dfu-util 05ac 828d 20702_828D.dfu
dfu-util, utility to flash dfu firmware into USB devices on OS X.
Based on original dfu-tool & dfu-programmer for Linux.
[i] Initiating DFU for USB device [05ac:828d].
The file 20702_828D.dfu contains a DFU suffix with the following properties:
BCD device: 0x0146
Product ID: 0x828D
Vendor ID: 0x05AC
BCD DFU: 0x0100
Length: 16
CRC: 0x7C8ECA6F
[i] USB [05ac:828d Љ v280] "Bluetooth USB Host Controller" by "Apple Inc."
[i] USB device has 1 configurations.
[i] DFU descriptor attributes 0x07 [Download, Upload, Manifestation Tolerant, Reserved bits: 0x00], Timeout: 5000, Transfer Size: 64
[i] Device State appIDLE, Status No error condition is present
[i] Transitioning from STATE_APP_IDLE into STATE_DFU_IDLE.
[!] Device is not in dfu mode (state appDETACH).
[!] Failed to enter DFU mode.