LAN8187_06 Datasheet, PDF(31/72 Page) SMSC Corporation – ±15kV ESD Protected MII/RMII Fast-Ethernet PHY with HP Auto-MDIX and SMSC flexPWRTM

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LAN8187_06 Datasheet, PDF (31/72 Pages) SMSC Corporation – ±15kV ESD Protected MII/RMII Fast-Ethernet PHY with HP Auto-MDIX and SMSC flexPWRTM

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Note: X = Dont Care.

Â±15kV ESD Protected MII/RMII Fast-Ethernet PHY with HP Auto-MDIX and SMSC flexPWRTM

Datasheet

Figure 4.4 Direct cable connection vs. Cross-over cable connection.

4.9

4.9.1

4.9.2

Internal +1.8V Regulator Disable

Part of the LAN8187/LAN8187I SMSC flexPWRTM technology is the ability to disable the internal +1.8v

regulator. This further increases the power savings as a more efficient external switching regulator can

provide the necessary +1.8v to the internal PHY circuitry.

Disable the Internal +1.8V Regulator

To disable the +1.8v internal regulator, a pulldown strapping resistor (see Table 4.4, âBoot Strapping

Configuration Resistors,â on page 32) is attached from REG_EN to VDDIO. When both VDDIO and

VDDA are within specification, the PHY will sample the REG_EN pin to determine if the internal

regulator should turn on. If the pin is grounded to VSS, then the internal regulator is off, and the system

needs to supply +1.8v +/- 10% to the VDD_CORE pin.

A 4.7uF low ESR and 0.1uF capacitor must be added to VDD_CORE and placed close to the PHY.

This capacitance provides decoupling of the external power supply noise and ensures stability of the

internal regulator.

Enable the Internal +1.8V Regulator

To enable the internal regulator, a pull-up resistor (see Table 4.4, âBoot Strapping Configuration

Resistors,â on page 32) to VDDIO needs to be added to the REG_EN pin.

A 4.7uF low ESR and 0.1uF capacitor must be added to VDD_CORE and placed close to the PHY.

This capacitance provides decoupling of the external power supply noise and ensures stability of the

internal regulator.

4.10 (TX_ER/TXD4)/nINT Strapping

The TX_ER, TXD4 and nINT functions share a common pin. There are two functional modes for this

pin, the TX_ER/TXD4 mode and nINT (interrupt) mode. The RXD3 pin is used to select one of these

two functional modes.

The RXD3 pin is latched on the rising edge of the internal reset (nreset) to select the mode. The

system designer must float the RXD3 pin for nINT mode or pull-low with an external resistor (see

Revision 1.0 (12-14-06)

DATASHEET

SMSC LAN8187/LAN8187I

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