LAN8710AI datasheet(38/82 Pages) MICROCHIP

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

Datasheet

Revision 1.4 (08-23-12)

SMSC LAN8710A/LAN8710Ai

DATASHEET

3.7.4

REGOFF: Internal +1.2V Regulator Configuration

The incorporation of flexPWR technology provides the ability to disable the internal +1.2V regulator.

When the regulator is disabled, an external +1.2V must be supplied to the VDDCR pin. Disabling the

internal +1.2V regulator makes it possible to reduce total system power, since an external switching

regulator with greater efficiency (versus the internal linear regulator) can be used to provide +1.2V to

the transceiver circuitry.

Note: Because the REGOFF configuration strap shares functionality with the LED1 pin, proper

consideration must also be given to the LED polarity. Refer to Section 3.8.1.1, "REGOFF and

LED1 Polarity Selection," on page 39 for additional information on the relation between

REGOFF and the LED1 polarity.

3.7.4.1

Disabling the Internal +1.2V Regulator

To disable the +1.2V internal regulator, a pull-up strapping resistor should be connected from the

REGOFF configuration strap to VDD2A. At power-on, after both VDDIO and VDD2A are within

specification, the transceiver will sample REGOFF to determine whether 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. The VDDIO voltage must be at least 80% of the

operating voltage level (1.44V when operating at 1.8V, 2.0V when operating at 2.5V, 2.64V when

operating at 3.3V) before voltage is applied to VDDCR. As described in Section 3.7.4.2, when

REGOFF is left floating or connected to VSS, the internal regulator is enabled and the system is not

required to supply +1.2V to the VDDCR pin.

3.7.4.2

Enabling the Internal +1.2V Regulator

The +1.2V for VDDCR is supplied by the on-chip regulator unless the transceiver is configured for the

regulator off mode using the REGOFF configuration strap as described in Section 3.7.4.1. By default,

the internal +1.2V regulator is enabled when REGOFF is floating (due to the internal pull-down

resistor). During power-on, if REGOFF is sampled below VIL, then the internal +1.2V regulator will turn

on and operate with power from the VDD2A pin.

3.7.5

nINTSEL: nINT/TXER/TXD4 Configuration

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

pin, the TXER/TXD4 mode and nINT (interrupt) mode. The nINTSEL configuration strap is latched at

POR and on the rising edge of the nRST. By default, nINTSEL is configured for nINT mode via the

internal pull-up resistor.

Note: Because the nINTSEL configuration strap shares functionality with the LED2 pin, proper

consideration must also be given to the LED polarity. Refer to Section 3.8.1.2, "nINTSEL and

LED2 Polarity Selection," on page 39 for additional information on the relation between

nINTSEL and the LED2 polarity.

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