WT41-A Datasheet, PDF (29/49 Pages) List of Unclassifed Manufacturers – Fully Qualified Bluetooth v2.1 + EDR end product

Figure 15: 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.
Figure 16: USB Interface Component Values
7.5 Bus-Powered Mode
In bus-powered mode, the application circuit draws its current from the 5V VBUS supply on the USB cable.
WT41 negotiates with the PC during the USB enumeration stage about how much current it is allowed to
consume. On power-up the device must not draw more than 100 mA but after being configured it can draw up
to 500 mA.
For WT41, the USB power descriptor should be altered to reflect the amount of power required. This is
accomplished by setting 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. By default for WT41 the setting is 300 mA.
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 the USB Specification.
Some applications may require soft start circuitry to limit inrush current if more than 10uF 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 WT41 supply pins will result in reduced receiver sensitivity
and a distorted RF transmit signal.
Bluegiga Technologies Oy
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