BC41B143A-DS-003PC Datasheet, PDF (61/94 Pages) List of Unclassifed Manufacturers – BlueCore 4-ROM Plug-n-Go Single Chip Bluetooth v2.0 + EDR System

Device Terminal Descriptions
10.5.5 Bus-Powered Mode
In bus-powered mode, the application circuit draws its current from the 5V VBUS supply on the USB cable.
BlueCore4-ROM Plug-n-Go 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, BlueCore4-ROM Plug-n-Go 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 BlueCore4-ROM Plug-n-Go will result
in reduced receive sensitivity and a distorted RF transmit signal.
BlueCore
USB_DP
USB_DN
USB_ON
R_s
R_s
R_vb1
D+
D-
VBUS
GND
Voltage
Regulator
Figure 10.14: USB Connections for Bus-Powered Mode
BC41B143A-ds-003Pc
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© Cambridge Silicon Radio Limited 2005
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