LAN8720AI datasheet(38/79 Pages) SMSC

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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

Datasheet

Revision 1.4 (08-23-12)

SMSC LAN8720A/LAN8720Ai

DATASHEET

pin is pulled low by an external pull-down resistor to select a logical low for nINTSEL, the LED2 output

will then be an active high output. Figure 3.11 details the LED2 polarity for each nINTSEL configuration.

Note: Refer to Section 3.7.4, "nINTSEL: nINT/REFCLKO Configuration," on page 33 for additional

information on the nINTSEL configuration strap.

3.8.2

Variable Voltage I/O

The device’s digital I/O pins are variable voltage, allowing them to take advantage of low power savings

from shrinking technologies. These pins can operate from a low I/O voltage of +1.62V up to +3.6V.

The applied I/O voltage must maintain its value with a tolerance of ± 10%. Varying the voltage up or

down after the transceiver has completed power-on reset can cause errors in the transceiver operation.

Refer to Chapter 5, "Operational Characteristics," on page 63 for additional information.

Note: Input signals must not be driven high before power is applied to the device.

3.8.3

Power-Down Modes

There are two device power-down modes: General Power-Down Mode and Energy Detect Power-

Down Mode. These modes are described in the following subsections.

3.8.3.1

General Power-Down

This power-down mode is controlled via the Power Down bit of the Basic Control Register. In this

mode, the entire transceiver (except the management interface) is powered-down and remains in this

mode as long as the Power Down bit is “1”. When the Power Down bit is cleared, the transceiver

powers up and is automatically reset.

3.8.3.2

Energy Detect Power-Down

This power-down mode is activated by setting the EDPWRDOWN bit of the Mode Control/Status

for the management interface, the SQUELCH circuit, and the ENERGYON logic). The ENERGYON

logic is used to detect the presence of valid energy from 100BASE-TX, 10BASE-T, or Auto-negotiation

signals.

In this mode, when the ENERGYON bit of the Mode Control/Status Register is low, the transceiver is

powered-down and nothing is transmitted. When energy is received via link pulses or packets, the

ENERGYON bit goes high and the transceiver powers-up. The device automatically resets into the

Figure 3.11 LED2/nINTSEL Polarity Configuration

~270 ohms

nINTSEL = 0

LED output = Active High

10K

~270 ohms

VDD2A

nINTSEL = 1

LED output = Active Low

LED2/nINTSEL

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