USB Pin Multiplexing
14-49
Universal Serial Bus Host
There are at least three different types of signaling used by commercially-
available USB transceivers to interface to a USB function controller.
OMAP5910 is designed for use with USB transceivers that use TXSE0 and
TXD signaling. OMAP5910 is not designed to interface directly with USB trans-
ceivers that use bidirectional signals between the transceiver and the USB
host controller or with USB transceivers that use TXD+ and TXD– signaling.
Because OMAP5910 does not provide a pin that connects to the USB host
controller port power control registers, some other mechanism must be used
if VBUS switching is required. Similarly, OMAP5910 does not provide any pins
that connect to the USB host controller overcurrent status bits, so some
other mechanism must be used if overcurrent sensing is required.
14.5.2 USB Function Controller Connectivity With USB Transceivers
To provide a robust USB solution, a system that provides a USB function con-
troller must implement certain features. These features include a USB-type B
receptacle, VBUS power detection, transient suppression, a controllable
pullup resistor to the D+ or D– line, and USB-compatible upstream port
transceiver. These elements are shown in Figure 14–4.
Figure 14–4. Typical USB Function Connections
USB
transceiver
Level
shifter
USB type B
receptacle
Transient
suppressor
USB function
controller
R1
R2
R3
R1, R2
R3
C1
U1
Value depends on transceiver
1.5K Ohm +/– 5%
Low ESR cap, minimum 120 uF
Transient suppressor, such as SN65220, SN65240, or SN75240
U1
+3.3 V
VBUS_DETECT
USB_PUEN
VBUS
D+
D–
R4
R5
R4, R5
Weak pulldown (optional, see text)