Highly Integrated Full Featured Hi-Speed USB 2.0 ULPI Transceiver
Datasheet
5.6.2.2
SessVld Comparator
The SessVld comparator is used when the transceiver is configured as both an A and B device. When
configured as an A device, the SessVld is used to detect Session Request protocol (SRP). When
configured as a B device, SessVld is used to detect the presence of VBUS. The SessVld interrupts
can be disabled by clearing this bit in both the USB Interrupt Enable Rising and USB Interrupt Enable
Falling registers. When the interrupts are disabled, the SessVld comparator is not disabled and its state
can be read in the USB Interrupt Status register. The SessVld comparator trip point is detailed in
Table 4.7.
Note: The OTG Supplement specifies a voltage range for A-Device Session Valid and B-Device
Session Valid comparator. The USB3320 transceiver combines the two comparators into one
and uses the narrower threshold range.
5.6.2.3
VbusVld Comparator
The final VBUS comparator is the VbusVld comparator. This comparator is only used when the
USB3320 is configured as an A-device. In the USB protocol the A-device supplies the VBUS voltage
and is responsible to ensure it remains within a specified voltage range. The VbusVld comparator can
be disabled by clearing this bit in both the USB Interrupt Enable Rising and USB Interrupt Enable
Falling registers. When disabled, bit 1 of the USB Interrupt Status register will return a 0. The VbusVld
comparator trip points are detailed in Table 4.7.
The internal VbusValid comparator is designed to ensure the VBUS voltage remains above 4.4V.
The USB3320 includes the external vbus valid indicator logic as detail in the ULPI Specification. The
external vbus valid indicator is tied to a logic one. The decoding of this logic is shown in Table 5.6
below. By default this logic is disabled.
Table 5.6 External VBUS Indicator Logic
USE
EXTERNAL
VBUS
INDICATOR
TYPICAL
APPLICATION
INDICATOR
PASS THRU
INDICATOR
COMPLEMENT
RXCMD VBUS VALID
ENCODING SOURCE
OTG Device
0
1
1
1
1
1
1
0
X
1
1
0
0
1
1
X
X
0
1
0
1
0
1
X
Internal VbusVld comparator (Default)
Fixed 1
Fixed 0
Internal VbusVld comparator.
Fixed 0
Fixed 1
Fixed 0
Standard Host
Standard
Peripheral
Internal VbusVld comparator. This
information should not be used by the
Link. (Note 5.3)
Note 5.3 A peripheral should not use VbusVld to begin operation. The peripheral should use
SessVld because the internal VbusVld threshold can be above the VBUS voltage required
for USB peripheral operation.
SMSC USB3320
Revision 1.0 (07-14-09)
DATA3S7HEET
SMSC [ SMSC CORPORATION ]
