BC352239A Datasheet, PDF (68/116 Pages) List of Unclassifed Manufacturers – BlueCore 3-Multimedia External

Device Terminal Descriptions
8.6.5 Bus-Powered Mode
In bus-powered mode the application circuit draws its current from the 5V VBUS supply on the USB cable.
BlueCore3-Multimedia External negotiates with the PC during the USB enumeration stage about how much
current it is allowed to consume.
For Class 2 Bluetooth applications, CSR recommends that the regulator used to derive 3.3V from VBUS is rated
at 100mA average current and should be able to handle peaks of 120mA without foldback or limiting. In bus-
powered mode, BlueCore3-Multimedia External requests 100mA during enumeration.
For Class 1 Bluetooth applications, the USB power descriptor should be altered to reflect the amount of power
required. This is accomplished by setting the PS Key PSKEY_USB_MAX_POWER (0x2c6). This is higher than
for a Class 2 application due to the extra current drawn by the Transmit RF PA.
When selecting a regulator, be aware that VBUS may go as low as 4.4V. The inrush current (when charging
reservoir and supply decoupling capacitors) is limited by the USB specification (see USB specification v1.1,
Section 7.2.4.1). Some applications may require soft start circuitry to limit inrush current if more than 10µF is
present between VBUS and GND.
The 5V VBUS line emerging from a PC is often electrically noisy. As well as regulation down to 3.3V and 1.8V,
applications should include careful filtering of the 5V line to attenuate noise that is above the voltage regulator
bandwidth. Excessive noise on the 1.8V supply to the analogue supply pins of BlueCore3-Multimedia External
will result in reduced receive sensitivity and a distorted RF transmit signal.
BlueCore3-Multimedia External
USB_DP
USB_DN
USB_ON
R_s
R_s
R _vb1
D+
D-
VBUS
GND
Voltage
Regulator
Figure 8.24: USB Connections for Bus-Powered Mode
Note:
USB_ON is shared with BlueCore3-Multimedia External PIO terminals.
Identifier
Value
Function
R_s
27Ω nominal
Impedance matching to USB cable
R_vb1
22kΩ 5%
VBUS ON sense divider
R_vb2
47kΩ 5%
VBUS ON sense divider
Table 8.18: USB Interface Component Values
BC352239A-ds-001Pc
© Cambridge Silicon Radio Limited 2004
Production Information
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