USB3500 SMSC Corporation, USB3500 Datasheet - Page 30

• Manufacturer Part Number: USB3500
• Description: Hi-Speed USB Host
• Manufacturer: SMSC Corporation

Revision 1.0 (04-04-05)
6.7.2.4
6.7.2.5
When the A-device is able to provide 8-100mA, it must ensure Vbus doesn’t go below 4.4 volts. If the
A-device can provide 100-500mA on VBUS, it must ensure that Vbus does not go below 4.75 volts.
The internal Vbus comparator is designed to ensure that Vbus remains above 4.4 volts. If the design
is required to supply over 100mA an external Vbus comparator or overcurrent fault detection should
be used.
Vbus Pull-up and Pull-down Resistors
In addition to the internal Vbus comparators, the USB3500 also includes the integrated VBUS pull-up
and pull-down resistors used for VBUS Pulsing. To discharge the VBUS voltage, so that a Session
Request can begin, the USB3500 provides a pull-down resistor from VBUS to Ground. This resistor is
controlled by the DISCHRGVBUS pin. The pull-up resistor is connected between VBUS and VDD3.3.
This resistor is used to pull Vbus above 2.1 volts to indicate to the A-Device that a USB session has
been requested. The state of the pull-up resistor is controlled by the CHRGVBUS pin. The Pull-Up and
Pull-Down resistor values are detailed in
Vbus Input Impedance
The OTG Supplement requires an A-Device that supports Session request protocol to have an input
impedance less than 100kohm and greater the 40kohm to ground. In addition, if configured as a B-
Device, the PHY cannot draw more then 150uA from Vbus. The USB3500 provides a 75kΩ nominal
resistance to ground which meets the above requirements.
DATASHEET
Table
30
Hi-Speed USB Host, Device or OTG PHY With UTMI+ Interface
5.7.
SMSC USB3500
Datasheet