isp1122 NXP Semiconductors, isp1122 Datasheet - Page 22

• Manufacturer Part Number: isp1122
• Description: Isp1122 Universal Serial Bus Stand-alone Hub
• Manufacturer: NXP Semiconductors

11. Hub power modes
Philips Semiconductors
9397 750 07002
Product specification
11.1.1 Self-powered hubs
11.1 Voltage drop requirements
Table 23: Configuration bits
[1]
[2]
[3]
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-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
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.
Bit
C0
C1
C2
C3
C4
C5
C7, C6
Default value at reset if no external EEPROM is present.
Modifies the Hub Descriptor field ‘bPwrOn2PwrGood’, see
Modifies the Hub Descriptor field ‘MaxPower’, see
Function
OPTION
INDV
reserved
PwrOn2PwrGood
string descriptor enable
internal analog overcurrent
detection enable
MaxPower
BUS
) to power the interface functions (hybrid-powered).
Rev. 03 — 29 March 2000
[3]
[2]
Value
(Bin)
see
see
0
0
1
0
1
0
1
00
1X
01
[1]
[1]
[1]
[1]
[1]
Table 4 “Mode selection”
Table 4 “Mode selection”
Table
Description
must always be programmed to logic 0
100 ms (bPwrOn2PwrGood = 32H)
500 ms (bPwrOn2PwrGood = FAH)
string descriptors disabled
string descriptors enabled (strings:
“Philips Semiconductors”, “ISP1122”)
internal analog overcurrent detection
circuit disabled; overcurrent pins OCn
function as digital inputs (TTL level)
internal analog overcurrent detection
circuit enabled
100 mA (MaxPower = 32H)
500 mA (MaxPower = FAH)
0 mA (MaxPower = 00H)
14.
Table
Table
14.
4).
USB stand-alone hub
© Philips Electronics N.V. 2000. All rights reserved.
ISP1122
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