BC41B143A-DS-001PE Datasheet, PDF (67/102 Pages) List of Unclassifed Manufacturers – BlueCpre 4-ROM Single Chip Bluetooth v2.0 System with EDR

Device Terminal Descriptions
10.5.4 Self Powered Mode
In self powered mode, the circuit is powered from its own power supply and not from the VBUS (5V) line of the
USB cable. It draws only a small leakage current (below 0.5mA) from VBUS on the USB cable. This is the easier
mode for which to design for, as the design is not limited by the power that can be drawn from the USB hub or
root port. However, it requires that VBUS be connected to BlueCore4-ROM via a resistor network (R_vb1 and R_vb2),
so BlueCore4-ROM can detect when VBUS is powered up. BlueCore4-ROM will not pull USB_DP high when
VBUS is off.
Self powered USB designs (powered from a battery or PSU) must ensure that a PIO line is allocated for USB
pull-up purposes. A 1.5K 5% pull-up resistor between USB_DP and the selected PIO line should be fitted to the
design. Failure to fit this resistor may result in the design failing to be USB compliant in self powered mode. The
internal pull-up in BlueCore is only suitable for bus powered USB devices i.e. dongles.
BlueCore4-ROM
PIO
USB_DP
USB_DN
USB_ON
1.5KΩ 5%
R_s
R_s
R_vb1
R_vb2
D+
D-
VBUS
GND
Figure 10.14: USB Connections for Self Powered Mode
The terminal marked USB_ON can be any free PIO pin. The PIO pin selected must be registered by setting
PSKEY_USB_PIO_VBUS to the corresponding pin number.
Note:
USB_ON is shared with BlueCore4-ROM 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 10.7: USB Interface Component Values
BC41B143A-ds-001Pe
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Production Information
© Cambridge Silicon Radio Limited 2005
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