USB 2.0
Datasheet
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| Table 5.2 USB251x Pin Descriptions (continued) |
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| SYMBOL | TYPE |
| DESCRIPTION |
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| DOWNSTREAM USB 2.0 INTERFACES (continued) |
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| LED_B_N[2:1] / | I/O12 |
| Enhanced Indicator Port LED for ports 1 and 2 |
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| Enhanced indicator LED for ports 1 and 2. This pin will be active low when |
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| LED support is enabled via EEPROM or SMBus. |
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| BOOST[1:0] |
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| If this strap option is enabled by package and configuration settings (see |
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| Table 8.1, "Hub Configuration Options"), this pin will be sampled at RESET_N |
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| negation to determine if all PHY ports (upstream and downstream) operate at |
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| a normal or boosted electrical level. Also, the active state of the LEDs will be |
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| determined as follows: |
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| See Section 8.2.1.27, "Register F6h: Boost_Up," on page 45 and Section |
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| 8.2.1.29, "Register F8h: Boost_4:0," on page 47 for more information. |
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| BOOST[1:0] = BOOST_IOUT[1:0] |
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| BOOST[1:0] = ‘00’, |
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| LED_B_N[2] is active high, |
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| LED_B_N[1] is active high. |
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| BOOST[1:0] = ‘01’, |
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| LED_B_N[2] is active high, |
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| LED_B_N[1] is active low. |
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| BOOST[1:0] = ‘10’, |
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| LED_B_N[2] is active low, |
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| LED_B_N[1] is active high. |
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| BOOST[1:0] = ‘11’, |
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| LED_B_N[2] is active low, |
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| LED_B_N[1] is active low. |
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| PRTPWR_POL | IPU |
| Port Power Polarity Strapping |
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| Port Power Polarity strapping determination for the active signal polarity of |
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| the [x:1]PRTPWR pins. |
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| While RESET_N is asserted, the logic state of this pin will (through the use |
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| of internal combinatorial logic) determine the active state of the PRTPWR |
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| pins in order to ensure that downstream port power is not inadvertently |
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| enabled to inactive ports during a hardware reset. |
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| When RESET_N is negated, the logic value will be latched internally, and will |
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| retain the active signal polarity for the PRTPWR[x:1] pins. |
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| ‘1’ = PRTPWR[x:1]_P/N pins have an active ‘high’ polarity |
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| ‘0’ = PRTPWR[x:1]_P/N pins have an active ‘low’ polarity |
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| Warning: Active low port power controllers may glitch the downstream port |
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| power when the system power is first applied. Care should be taken when |
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| designing with active low components. |
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| When PRTPWR_POL is not an available pin on the package, the hub will only |
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| support active high power controllers. |
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| OCS_N[x:1] | IPU |
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| Input from external current monitor indicating an |
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| RBIAS |
| USB Transceiver Bias |
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| A 12.0 kΩ (+/- 1%) resistor is attached from ground to this pin to set the |
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| transceiver’s internal bias settings. |
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Revision 1.0 |
| 24 | SMSC USB251x | |||
DATASHEET