Hub power modes, 1 voltage drop requirements, 1 self-powered hubs – Philips Universal Serial Bus ISP1122 User Manual

Page 22: Table 23, In this case, Modes 0, 1, 2, 4, 5, 6); see, Isp1122, Philips semiconductors

Philips Semiconductors

ISP1122

USB stand-alone hub

Product specification

Rev. 03 — 29 March 2000

22 of 48

9397 750 07002

[1]

Default value at reset if no external EEPROM is present.

[2]

Modifies the Hub Descriptor field ‘bPwrOn2PwrGood’, see

Table 14

[3]

Modifies the Hub Descriptor field ‘MaxPower’, see

Table 14

11. Hub power modes

USB hubs can either be self-powered or bus-powered.

Self-powered — Self-powered hubs have a 5 V local power supply on board which
provide power to the hub and the downstream ports. The

USB Specification Rev. 1.1

requires that these hubs limit the current to 500 mA per downstream port and report
overcurrent conditions to the host. The hub may optionally draw 100 mA from the
USB supply (V

BUS

) to power the interface functions (hybrid-powered).

Bus-powered — Bus-powered hubs obtain all power from the host or an upstream
self-powered hub. The maximum current is 100 mA per downstream port. Current
limiting and reporting of overcurrent conditions are both optional.

Power switching of downstream ports can be done individually or ganged, where all
ports are switched simultaneously with one power switch. The ISP1122 supports both
modes, which can be selected using input INDV (see

Table 4

11.1 Voltage drop requirements

11.1.1

Self-powered hubs

Self-powered hubs are required to provide a minimum of 4.75 V to its output port
connectors at all legal load conditions. To comply with Underwriters Laboratory Inc.
(UL) safety requirements, the power from any port must be limited to 25 W (5 A at
5 V). Overcurrent protection may be implemented on a global or individual basis.

Table 23: Configuration bits

Bit

Function

Value
(Bin)

Description

OPTION

see

Table 4 “Mode selection”

INDV

see

Table 4 “Mode selection”

reserved