SMSC LAN8710, LAN8710i, MII 10/100, RMII 10/100 4.9Internal +1.2V Regulator Disable, 4.9.1Disable the Internal +1.2V Regulator, 4.9.2Enable the Internal +1.2V Regulator

MII/RMII 10/100 Ethernet Transceiver with HP Auto-MDIX and flexPWR® Technology in a Small Footprint

Datasheet

The internal logic of the device detects the TX and RX pins of the connecting device. Since the RX and TX line pairs are interchangeable, special PCB design considerations are needed to accommodate the symmetrical magnetics and termination of an Auto-MDIX design.

The Auto-MDIX function can be disabled using the Special Control/Status Indications register (bit 27.15).

Figure 4.4 Direct Cable Connection vs. Cross-over Cable Connection

4.9Internal +1.2V Regulator Disable

One feature of the flexPWR technology is the ability to configure the internal 1.2V regulator off. When the regulator is disabled, external 1.2V must be supplied to VDDCR. This makes it possible to reduce total system power, since an external switching regulator with greater efficiency than the internal linear regulator may be used to provide the +1.2V to the transceiver circuitry.

4.9.1Disable the Internal +1.2V Regulator

To disable the +1.2V internal regulator, a pullup strapping resistor is connected from LED1/REGOFF to VDD2A. At power-on, after both VDDIO and VDD2A are within specification, the transceiver will sample the LED1/REGOFF pin to determine if the internal regulator should turn on. If the pin is sampled at a voltage greater than VIH, then the internal regulator is disabled, and the system must supply +1.2V to the VDDCR pin. As described in Section 4.9.2, when the LED1/REGOFF pin is left floating or connected to VSS, then the internal regulator is enabled and the system is not required to supply +1.2V to the VDDCR pin.

4.9.2Enable the Internal +1.2V Regulator

The 1.2V for VDDCR is supplied by the on-chip regulator unless the transceiver is configured for regulator off mode using the LED1/REGOFF pin as described in Section 4.9.1. By default, the internal +1.2V regulator is enabled when the LED1/REGOFF pin is floating. As shown in Table 7.10, an internal pull-down resistor straps the regulator on if the LED1/REGOFF pin is floating.

During VDDIO and VDDA power-on, if the LED1/REGOFF pin is sampled below VIL, then the internal +1.2V regulator will turn on and operate with power from the VDD2A pin.

SMSC LAN8710/LAN8710i	31	Revision 1.0 (04-15-09)
	DATASHEET